Epidemiological and clinical features of laboratory-diagnosed severe fever with thrombocytopenia syndrome in China, 2011-17: a prospective observational study

Identification of early prognostic biomarkers in Severe Fever with Thrombocytopenia Syndrome using machine learning algorithms

OBJECTIVE

We aimed at identifying acute phase biomarkers in Severe Fever with Thrombocytopenia Syndrome (SFTS), and to establish a model to predict mortality outcomes.

METHODS

A retrospective analysis was conducted on multicenter clinical data. Group-based trajectory modeling (GBTM) was utilized to demonstrate the overall trend of laboratory indicators and their correlation with mortality. Six different machine learning algorithms were employed to develop prognostic models based on the clinical features during the acute phase, which were reduced using Lasso regression.

RESULTS

Seven indicators (ALT, AST, BUN, LDH, a-HBDH, DD, and PLT) at 7-10 days post-onset and their change slopes were found to be crucial during disease progression. These, along with other clinical features, were reduced to 8 variables using Lasso regression for model construction. The random forest model demonstrated the best performance in both internal validation (AUC: 0.961) and external validation (AUC: 0.948). Decision Curve Analysis indicated a good balance between model benefits and risks.

CONCLUSIONS

a-HBDH and its change slope along with central nervous symptom manifestations within 7-10 days after onset accurately predicted mortality in SFTS. Various algorithms provided a comprehensive overview of disease progression and constructed more stable and efficient models.

Concurrent severe fever with thrombocytopenia syndrome virus outbreaks on multiple fox farms, China, 2023

The role of farmed animals in the viral spillover from wild animals to humans is of growing importance. Between July and September of 2023 infectious disease outbreaks were reported on six Arctic fox (Vulpes lagopus) farms in Shandong and Liaoning provinces, China, which lasted for 2-3 months and resulted in tens to hundreds of fatalities per farm. Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV) was identified in tissue/organ and swab samples from all the 13 foxes collected from these farms. These animals exhibited loss of appetite and weight loss, finally resulting in death. In autopsy and histopathology, prominently enlarged spleens and extensive multi-organ hemorrhage were observed, respectively, indicating severe systemic effects. Viral loads were detected in various tissues/organs, including brains from 9 of the 10 foxes. SFTSV was also detected in serum, anal swabs, as well as in environmental samples, including residual food in troughs used by dying foxes in follow-up studies at two farms. The 13 newly sequenced SFTSV genomes shared >99.43% nucleotide identity with human strains from China. Phylogenetic analyses showed that the 13 sequences belonged to three genotypes, and that two sequences from Liaoning were genomic reassortants, indicative of multiple sources and introduction events. This study provides the first evidence of SFTSV infection, multi-tissue tropism, and pathogenicity in farmed foxes, representing an expanded virus host range. However, the widespread circulation of different genotypes of SFTSV in farmed animals from different provinces and the diverse transmission routes, highlight its increasing and noticeable public health risk in China.

Whole-genome sequence analysis of SFTS bunyavirus in Huzhou, China

Severe fever with thrombocytopenia syndrome (SFTS), a tick-borne emerging infectious disease caused by SFTS virus (SFTSV), is a growing public health threat due to its high mortality rate. To understand the genomic characteristics of SFTSV samples isolated in Huzhou, China, the full-length genomes of Huzhou SFTSV isolates obtained between February 1, 2019 and December 30, 2023 were sequenced, and the gene loci, evolution, and sequence identity of the genome sequences were analyzed using MEGA. The complete genome sequences of seven SFTSV samples were obtained successfully. The full-length genome of each isolate was 11 490 bp in length, composed of a large (L) segment of 6368 bp, medium (M) segment of 3378 bp, and small (S) segment of 1744 bp. The SFTSV samples isolated in Huzhou belonged to multiple genotypes, but were mainly of type D. Each subtype showed nucleotide sequence and amino acid sequence identities of more than 93.67% and 97.18%, respectively, with the syngeneic human host reference strain and more than 93.67% and 97.76%, respectively, with the syngeneic tick-derived host reference strain. Nucleotide sequence analysis of SFTSV isolates from Huzhou showed mutations in genes on all three segments, with those on the M segment showing the highest mutation rate. The nucleotide variations were mainly base transversions. Further studies of the distribution of SFTSV genotypes, sites of nucleotide mutations, and amino acid variations are required.

Development and validation of a novel mortality risk stratification simplified scoring scale for severe fever with thrombocytopenia syndrome

OBJECTIVES

The global incidence of severe fever with thrombocytopenia syndrome (SFTS) has markedly increased over the past decade. There is an urgent need to establish a reliable scoring system for predicting the mortality of patients with SFTS.

METHODS

In this ambispective study, 714 patients with SFTS were recruited from 11 sites in China. Among these, 544 patients hospitalized for SFTS from May 2012 to June 2022 were included retrospectively in the training cohort, and 170 were prospectively enrolled between April 2021 and November 2023 in the validation cohort. Logistic regression analysis was performed to identify risk factors for 30-day mortality. A nomogram model (SFTS-logistic model) and a simplified scoring system (SFTS-Wuhan model) were established for predicting mortality. The performance of these models in terms of calibration, discrimination, and clinical utility was evaluated and validated.

RESULTS

The 30-day mortality rate was 12.89% (92/714). The mean age was 65 years old (interquartile range, 57-71), and 322 (45.10%) patients were male. The SFTS-logistic model and SFTS-Wuhan model were developed based on seven independent risk factors, including age (adjusted OR [AOR], 1.062; 95% CI, 1.019-1.106), temperature at admission (AOR, 1.599; 95% CI, 1.095-2.336), white blood cell count (AOR, 0.799; 95% CI, 0.653-0.978), platelet count (AOR, 0.977, 95% CI, 0.959-0.996), aspartate aminotransferase (AOR, 1.001, 95% CI, 1.000-1.003), creatinine (AOR, 1.006; 95% CI, 1.001-1.011), and vasopressors use (AOR, 6.270; 95% CI, 1.397-28.146). Both models demonstrated good discrimination with areas under the receiver operating characteristic curve above 0.84, satisfactory calibration, and comparable clinical net benefit in the training and validation cohorts.

DISCUSSION

The prognostic scoring model and its simplified surrogate can serve as robust tools for mortality risk stratification in SFTS, allowing the early identification of high-risk patients.

Identification of early prediction biomarkers of severity in patients with severe fever with thrombocytopenia syndrome based on plasma proteomics

Background

Severe fever with thrombocytopenia syndrome (SFTS) is a newly emerging infectious disease. Given its rapid disease progression and high mortality rate, early warning is crucial in improving the outcomes, However, to date, relevant comprehensive predictors or an effective prediction model are still poorly explored.

Methods

A plasma proteomic profile was performed at early stages in patients with SFTS. Functional clustering analysis was used to select the candidate proteins and then validate their expression by ELISA. A cohort consisting of 190 patients with SFTS was used to develop the predictive model for severe illness and subsequently validate it in a new cohort consisting of 93 patients with SFTS.

Results

A significant increase in plasma proteins associated with various functional clusters, such as the proteasomal protein catabolic process, phagocytosis, and humoral immune response, was observed in severe SFTS patients. High levels of four proteins including NID1, HSP90α, PSMA1, and VCAM1 were strongly correlated with multi-organ damage and disease progression. A prediction model was developed at the early stage to accurately predict severe conditions with the area under the curve of 0.931 (95% CI, 0.885, 0.963).

Conclusion

The proteomic signatures identified in this study provide insights into the potential pathogenesis of SFTS. The predictive models have substantial clinical implications for the early identification of SFTS patients who may progress to severe conditions.

Inflammatory Burden Index as a Predictor of In-Hospital Mortality in Patients With Severe Fever With Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an infectious disease caused by a novel bunyavirus that poses a significant threat to human health. The aim of this study was to identify a precise and user-friendly indicator for predicting the mortality of patients with SFTS. We retrospectively analyzed data from 181 hospitalized patients with SFTS. Inflammatory markers, including the neutrophil-to-lymphocyte ratio (NLR), lymphocyte-to-monocyte ratio (LMR), platelet-to-lymphocyte ratio (PLR), systemic inflammation index (SII), systemic inflammatory response index (SIRI), C-reactive protein-to-albumin ratio (CAR), and inflammatory burden index (IBI), were compared between the survival group and the nonsurvival group. A receiver operating characteristic (ROC) curve was used to evaluate the diagnostic value of the IBI for the poor prognosis of SFTS patients. Survival analysis was performed using the Kaplan‒Meier (KM) method. Univariate and multivariate Cox regression models were used to explore factors influencing the prognosis of hospitalized patients with SFTS. The results indicate that patients with high IBI had significantly higher mortality rates than those with low IBI. ROC curve analysis revealed that the IBI had better predictive value than the other indicators did, with an optimal cutoff value of 0.878. Kaplan-Meier survival analysis revealed that patients with high IBI had higher mortality rates and shorter survival times. Multivariate Cox regression analysis demonstrated that the IBI was an independent risk factor for poor prognosis in patients with SFTS. Therefore, the IBI can be used to help clinicians identify high-risk individuals and implement timely therapeutic interventions.

Geriatric Nutritional Risk Index Plays Important Role in Predicting In-Hospital Mortality in Patients With Severe Fever With Thrombocytopenia Syndrome: A Multi-Center Observational Study

Geriatric nutritional risk index (GNRI) has been proposed as a reliable indicator of nutritional state and, when decreased, is closely associated with the severity and mortality risk of infectious disease. The current study retrospectively recruited patients who were admitted for SFTS from January 1, 2011 to January 1, 2024 at six medical centers. Two hundred and eighty-two patients with SFTS who met the study protocol were finally enrolled in this study. Sixty patients suffered in-hospital death during hospitalization, with a mortality rate of 21.3%. After adjustment of multiple models, GNRI remained a significant predictor of in-hospital death, either examining HR by evaluating 1-unit decrease of GNRI or by taking the higher median of GNRI as reference (all p < 0.05). GNRI displayed a moderate-to-high strength in predicting in-hospital death, with an area under the receiver operating characteristic curve (AUC) of 0.791 [95% confidence interval (CI) 0.725-0.857, p < 0.001]. The addition of GNRI to a former established model exhibited significant improvement in the predictive value for in-hospital death. GNRI, an important indicator simply calculated from ALB and BMI, is significantly and independently related to the risk of in-hospital death in patients with SFTS.

Two-transcript signature for differentiation and clinical outcomes in severe fever with thrombocytopenia syndrome (SFTS) patients: a double-blind, multicenter, validation study

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with a high mortality rate that is often underdiagnosed due to the limitations of current laboratory testing. Timely diagnosis and early identification of severe cases are crucial to improving patient outcomes and overall survival rates. This study aimed to evaluate the efficacy of two transcripts, IFI44L and PI3, in the early differentiation between SFTS virus (SFTSV) infection and bacterial sepsis, as well as in the prompt identification of severe cases during epidemic seasons. In a prospective study conducted between 1 May 2021 and 30 September 2022, we enrolled 225 patients who presented with acute fever and thrombocytopenia at four hospitals in Shandong Province, China. The two-transcript signature provided a clear distinction between SFTS and bacterial infection, achieving an area under the receiver operating characteristic curve of 0.961 (95% confidence interval [95% CI] 0.916-0.986), outperforming C-reactive protein (0.810 [95% CI 0.738-0.870]) and procalcitonin (0.764 [95% CI 0.687-0.830]). Importantly, the relative expression of the IFI44L gene was significantly elevated in fatal SFTS cases, with an area under the curve (AUC) of 0.820 (95% CI 0.727-0.914), indicating its potential as an early prognostic marker. Additionally, IFI44L and PI3 were identified as potential biomarkers for distinguishing SFTS patients with and without invasive pulmonary aspergillosis, with AUC values of 0.817 and 0.753, respectively. Our findings demonstrate that the two-transcript signature effectively distinguishes SFTSV infection from bacterial sepsis and helps identify high-risk individuals, guiding appropriate treatment during SFTS outbreak.

Relationship between meteorological factors and the incidence of severe fever with thrombocytopenia syndrome: a systematic review and meta-analysis

OBJECTIVE

Although meteorological factors are connected with severe fever with thrombocytopenia syndrome (SFTS) incidence, available findings have been inconsistent. This study was performed to systematically evaluate the correlation between meteorological factors and SFTS incidence.

METHODS

We performed a thorough literature search in PubMed, Web of Science, Embase, Cochrane Library, and Chinese databases from databases initiatives to November 30, 2024. Literature was searched for correlation between meteorological factors and SFTS incidence. Two researchers screened the retrieved literature based on exclusion and inclusion criteria. Finally, data extraction and quality evaluation were carried out for the included literature, and meta-analysis was executed applying the R package (4.4.1).

RESULTS

A total of 404 relevant literature were retrieved, and 12 studies were enrolled in the meta-analysis. Both average temperature (rs=0.73, 95%CI 0.63-0.81, P<0.001), average relative humidity (rs=0.46, 95%CI 0.32-0.57, P < 0.001), cumulative precipitation (rs=0.49, 95%CI 0.33-0.62, P < 0.001), average precipitation (rs=0.48, 95%CI 0.21-0.68, P < 0.001), and sunlight (rs=0.34, 95%CI 0.11-0.53, P < 0.01) were positively correlated with SFTS incidence. The average atmospheric pressure was negatively correlated with SFTS incidence (rs= -0.69, 95%CI -0.78- -0.59, P < 0.001), and the average wind speed was not significantly correlated with SFTS incidence (P > 0.05).

CONCLUSIONS

Factors such as temperature, humidity, precipitation, sunshine duration, and atmospheric pressure are related to the incidence of SFTS with a certain lag effect. Future studies on the relationship between meteorological factors and the incidence of SFTS should fully consider human activities and environmental factors, and explore the pathogenesis and transmission mechanisms in greater depth, so as to provide targeted preventive measures.

CLINICAL TRIAL NUMBER

Not applicable.

Prediction of Prognosis in Patients with Severe Fever with Thrombocytopenia Syndrome

This study aimed to understand the clinical characteristics of severe fever with thrombocytopenia syndrome (SFTS) and identify the risk factors for prognosis. In this retrospective study, we collected epidemiological, demographic, clinical, and laboratory data from 101 patients with SFTS. Patients were divided into survival and deceased groups, and a logistic regression model was used to evaluate the association between the predictors and prognostic variables. A joint detection factor model was constructed, and a receiver operating characteristic curve was drawn. A nomogram was established using the R language, and its efficiency in diagnosing SFTS was evaluated using a calibration curve. Patients in the deceased group were more likely to be older, have a shorter hospitalization stay, and have renal and multiple organ failure than those in the survival group. Statistically significant differences were observed in the neutrophil percentage, lymphocyte percentage, neutrophil-to-lymphocyte ratio, platelet (PLT) count, aspartate aminotransferase (AST)/alanine transaminase (ALT) ratio, AST, blood urea nitrogen, lactate dehydrogenase, hydroxybutyrate dehydrogenase, thromboplastin time, and activated partial thromboplastin time between the two groups. Lymphocyte percentage, PLT count, and the AST/ALT ratio were independent risk factors for mortality in patients with SFTS. Thus, we established a prediction model for SFTS mortality with good efficiency.

Risk Factors for Co-Infections in Patients With Severe Fever With Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging viral hemorrhagic fever with a high fatality rate and notable public health impact, caused by a novel phlebovirus, primarily transmitted through infected tick bites. This study aimed to assess the prevalence of co-infections among hospitalized patients with SFTS, characterize isolated pathogens, and evaluate demographics, clinical features, and laboratory variations to identify potential risk factors for co-infections. In a cohort of 78 SFTS patients categorized into co-infection and non-co-infection groups, 44.9% (35/78) experienced co-infections, with a 25.7% mortality rate in that subgroup. Pulmonary and bloodstream infections, particularly fungal infections, were most common, and earlier onset of co-infections correlated with higher fatality. Univariable logistic regression identified significant risk factors, followed by multivariable analysis to determine independent predictors. Changes in mental status, hemorrhage, deep venous or arterial catheterization, mechanical ventilation, activated partial thromboplastin time (APTT) > 55 s, albumin < 37.5 g/L, interleukin-6 > 18.700 pg/mL, and interleukin-10 > 21.300 pg/mL emerged as significant risk factors, with hemorrhagic symptoms and low albumin remaining independent predictors. Internal validation through bootstrap resampling yielded a mean area under the receiver operating characteristic curve of 0.795 (95% CI: 0.706-0.868). These findings suggest that early recognition of these predictors may improve co-infection management in SFTS patients, leading to better clinical outcomes and more informed clinical decisions.

Early therapy contributes to the normalization of platelet in patients with severe fever with thrombocytopenia syndrome during the convalescent phase

BACKGROUND

Platelet recovery was an important prognostic indicator in severe fever with thrombocytopenia syndrome (SFTS). This study focused on risk factors affecting platelet recovery in surviving SFTS patients, which can assist clinicians in the early screening of patients associated with a greater risk of mortality.

METHOD

We retrospectively analyzed the clinical data of SFTS patients admitted to Yantai Qishan Hospital throughout 2023. According to the Diagnosis and Treatment Guideline (2023 edition), the platelet recovery in 14 days was set as outcome. The multivariate Cox regression was used to identify independent risk factors affecting platelet recovery and the Kaplan-Meier was performed to evaluate the probability of 14-day platelet recovery, using receiver operating characteristic (ROC) curve and area under the curve (AUC) to measure the model's performance, with clinical benefit assessed by decision curve analysis (DCA).

RESULTS

168 SFTS patients were enrolled in the study, with 76.2% (128/168) achieving platelet (PLT) recovery within 14 days. Independent risk factors were baseline PLT > 90 × 109/L (HR: 7.929, 95%CI: 1.066-58.990, P = 0.043), days from onset to admission >6 days (HR: 0.444, 95%CI: 0.259-0.763, P = 0.003) and baseline prothrombin time (PT) >13 s (HR: 0.547, 95%CI: 0.373-0.800, P = 0.002), with an AUC of 0.745 (95% CI: 0.656-0.834, P < 0.001). DCA demonstrated that when the recovery probability beyond approximately 50%, the clinical net benefit from focusing on the PLT stratification model consistently surpassed that from the all-intervention model. The nomogram further visualized the model.

CONCLUSION

Early diagnosis and timely therapy contributed to recovery during convalescence in SFTS patients, with baseline PT as a strong predictor.

Discovery and characterization of potent broadly neutralizing antibodies from human survivors of severe fever with thrombocytopenia syndrome

BACKGROUND

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne phlebovirus that causes viral hemorrhagic fever. Pandemic concerns have arisen due to the increased human-to-human transmission and high mortality rate, highlighting the urgent need for specific therapeutics.

METHODS

Our observational study characterized the memory B cell response to natural SFTSV infection in four survivors. Monoclonal antibodies (mAbs) targeting the SFTSV glycoprotein N (Gn) were isolated and tested for in vitro neutralizing activities and effects on virus binding. Structural analysis was performed to identify neutralizing epitopes recognized by the mAbs. Prophylactical and therapeutical protections were evaluated using a lethal SFTSV infection model.

FINDINGS

The selected mAbs exhibiting neutralizing activity primarily originate from the IGHV5-51 and IGHV3-30 germlines and target four distinct antigenic sites on SFTSV Gn. These elite mAbs effectively blocked the interaction between Gn and the cell receptor, preventing infections from five phylogenetically distinct SFTSV clades. Structural analysis revealed a novel neutralizing epitope located within SFTSV Gn domain I recognized by the elite mAbs. In mice of lethal infections with different SFTSV strains, administering a low dose of elite mAbs significantly improved survival rates in both prophylactic and therapeutic settings.

INTERPRETATION

This study identifies potent broadly neutralizing antibodies that holds promise for use in humans against SFTSV infection and highlights inhibition of receptor binding as a crucial mechanism for effective antibody-mediated neutralization against phleboviruses.

FUNDING

The National Key Research and Development Plan of China (2018YFE0200401, 2022YFC2303300), National Natural Science Foundation of China (81825019), China Postdoctoral Science Foundation (2023M741824).

Development of 111In-Labeled Monoclonal Antibodies Targeting SFTSV Structural Proteins for Molecular Imaging of SFTS Infectious Diseases by SPECT

No effective vaccines or treatments are currently available for severe fever with thrombocytopenia syndrome (SFTS), a fatal tick-borne infectious disease caused by the SFTS virus (SFTSV). This study evaluated the potential of 111In-labeled anti-SFTSV antibodies targeting SFTSV structural proteins as single-photon emission computed tomography (SPECT) imaging agents for the selective visualization of SFTSV-infected sites. This study used nuclear medicine imaging to elucidate the pathology of SFTS and assess its therapeutic efficacy. Immunostaining experiments confirmed that the anti-SFTSV antibody (N-mAb), which targets the N protein, specifically accumulated in SFTSV-infected Vero E6 cells. 111In-labeled N-mAb was successfully prepared using a diethylenetriaminepentaacetic acid (DTPA) chelator, resulting in [111In]In-DTPA-N-mAb with high radiochemical purity exceeding 95% and a radiochemical yield of 55%. Cell-binding assays using SFTSV-infected Vero E6 cells demonstrated that [111In]In-DTPA-N-mAb binding was detectable even without membrane permeabilization, with the binding intensity correlating with infection levels. In vivo studies using SFTSV-infected A129 mice showed high spleen accumulation of [111In]In-DTPA-N-mAb (87.5% ID/g), consistent with SFTSV tropism, compared to 12.3% ID/g in mock-infected mice. SPECT/CT imaging clearly revealed high radioactivity in these regions. Although nonspecific accumulation was noted in the liver and spleen, this issue may be mitigated through antibody modifications such as fragmentation or PEGylation. Overall, [111In]In-DTPA-N-mAb is a promising imaging agent for non-invasive visualization of SFTSV-infected sites and may aid in elucidating SFTS pathology and assessing therapeutic efficacy.

Host specific sphingomyelin is critical for replication of diverse RNA viruses

Lipids and lipid metabolism play an important role in RNA virus replication, which typically occurs on host cell endomembrane structures in the cytoplasm through mechanisms that are not yet fully identified. We conducted genome-scale CRISPR screening and identified sphingomyelin synthase 1 (SMS1; encoded by SGMS1) as a critical host factor for infection by severe fever with thrombocytopenia syndrome virus (SFTSV). SGMS1 knockout reduced sphingomyelin (SM) (d18:1/16:1) levels, inhibiting SFTSV replication. A helix-turn-helix motif in SFTSV RNA-dependent RNA polymerase (RdRp) directly binds to SM(d18:1/16:1) in Golgi apparatus, which was also observed in SARS-CoV-2 and lymphocytic choriomeningitis virus (LCMV), both showing inhibited replication in SGMS1-KO cells. SM metabolic disturbance is associated with disease severity of viral infections. We designed a novel SMS1 inhibitor that protects mice against lethal SFTSV infection and reduce SARS-CoV-2 replication and pathogenesis. These findings highlight the critical role of SMS1 and SM(d18:1/16:1) in RNA virus replication, suggesting a broad-spectrum antiviral strategy.

Limitations of a proper SFTSV mouse model using human C-type lectin receptors

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne virus with a human mortality rate of up to 30%, posing a significant threat to public health. However, the lack of suitable research models has impeded the development of effective human vaccines. In this study, we engineered transgenic mice (3xTg) using a novel construct that simultaneously expresses three C-type Lectin receptors, identified as critical SFTSV entry receptors. While this construct substantially enhanced viral binding and infection in BJAB cells, the 3xTg mice exhibited only limited SFTSV replication in the lymph nodes and spleen, without significant impacts on morbidity or mortality. These findings highlight that the overexpression of entry receptors alone is insufficient to fully recapitulate human SFTSV infection in mice. Moreover, our results reveal that the introduction of multiple entry receptors does not necessarily translate to enhanced infection efficacy. This underscores the need for further investigation into the interplay between SFTSV entry mechanisms and host factors to develop more robust mouse models. Advancing such models will be crucial for unraveling the pathogenesis of SFTS pathology and improving strategies for its prevention and treatment in humans.

A global lipid map of severe fever with thrombocytopenia syndrome virus infection reveals glycerophospholipids as novel prognosis biomarkers

Severe fever with thrombocytopenia syndrome (SFTS) is a rapidly progressing infectious disease caused by a novel bunyavirus characterized by high fever, thrombocytopenia, and multiple organ damage. While lipids play an important role in viral infections, the specific alterations in lipid metabolism during SFTSV infection remain unclear. This study aimed to elucidate the global lipid metabolic profiles of SFTS patients with mild, severe, and fatal outcomes. A total of 60 SFTS patients, consisting of 30 mild, 15 severe and 15 fatal patients, and 30 healthy controls, were enrolled for the investigation of global lipidomics in serum using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Our findings revealed global alterations in the lipid signature induced by SFTSV infection and further confirmed that the glycerophospholipid metabolism pathway was profoundly affected during the progression of mild, severe, and fatal outcomes in SFTS patients. Importantly, LysoPC (20:0) and LysoPC (P-16:0) are strongly correlated with the clinical parameters of SFTSV infection. Furthermore, we demonstrated the substantial prognostic value of LysoPC (20:0) and LysoPC (P-16:0) by receiver operating characteristic (ROC) curve analysis, providing evidence for their remarkable value as prognostic biomarkers for predicting SFTS clinical outcomes. In particular, LysoPC (20:0) and LysoPC (P-16:0), along with APTT, yielded superior prognostic performance for fatal SFTS [area under the curve (AUC) = 98.4%], outperforming routine clinical parameters. Collectively, our findings revealed the lipidomic landscape after SFTSV infection, which offers new insights into the mechanisms of SFTS disease progression and suggests that targeting lipid metabolism may serve as a potential therapeutic strategy.

IMPORTANCE

This study systematically investigated the lipid landscape profile of SFTS-infected patients with different clinical outcomes. Our results revealed a global alteration in the lipid signature, particularly the glycerophospholipid metabolic pathway, induced by SFTSV infection. Notably, LysoPC (20:0) and LysoPC (P-16:0) presented remarkable prognostic value as novel biomarkers for SFTSV infection and may contribute to the prognosis of SFTS progression and appropriate interventions.

Analysis of Changes in Viral Load and Inflammatory Cytokines, as Well as the Occurrence of Secondary Infections, in SFTS Patients Treated with Specific Treatments: A Prospective Multicenter Cohort Study

Severe fever with thrombocytopenia syndrome (SFTS) is an acute febrile illness caused by the SFTS virus (SFTSV). We conducted this study to propose a scientific evidence-based treatment that can improve prognosis through changes in viral load and inflammatory cytokines according to the specific treatment of SFTS patients. This prospective and observational study was conducted at 14 tertiary referral hospitals, which are located in SFTS endemic areas in Korea, from 1 May 2018 to 31 October 2020. Patients of any age were eligible for inclusion if they were polymerase chain reaction positive against SFTSV, or showed a four-fold or higher increase in IgG antibody titers between two serum samples collected during the acute and convalescent phases. On the other hand, patients with other tick-borne infections were excluded. In total, 79 patients were included in the study. The viral load of the group treated with steroids was 3.39, 3.21, and 1.36 log10 RNA copies/reaction at each week since the onset of symptoms, and the viral load in patients treated with plasma exchange was 4.47, 2.60, and 2.00 log10 RNA copies/reaction at each week after symptom onset. The inflammatory cytokines were not reduced effectively by any specific treatment except IVIG for the entire treatment period. Secondary infections according to pathogens revealed four bacterial (26.7%) and one fungal (6.7%) infection in the steroid group. The viral load of SFTSV and inflammatory cytokines cannot be decreased by steroid and plasma exchange treatments. Secondary bacterial infections can occur when steroids are administered for the treatment of SFTS. Therefore, caution should be exercised when choosing treatment strategies for SFTS.

Establishment of an Early Prediction Model for Severe Fever With Thrombocytopenia Syndrome-Associated Encephalitis

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease primarily transmitted by ticks. The development of encephalitis in SFTS patients significantly increases the risk of adverse outcomes. However, the understanding of SFTS-associated encephalitis (SFTSAE) is still limited. This study aimed to identify the clinical characteristics of SFTSAE and develop a predictive model for early detection.

METHODS

We retrospectively collected data from 220 SFTS patients admitted to Nanjing Drum Tower Hospital between May 2019 and January 2024. The patients were first randomly divided into a training set (154 people, 70%) and a validation set (66 people, 30%). The patients in the training set were divided into SFTSAE and non-SFTSAE groups according to the presence of encephalitis. A prediction model was constructed using the training set: important clinical parameters were selected using univariate logistic regression, and then multivariate logistic regression was performed to determine the independent risk factors for SFTSAE. A prediction model was constructed using these independent risk factors. Finally, the validation set was used to verify the predictive ability of the model.

RESULTS

Age, C-reactive protein, d-dimer, and viral load were independent risk factors for SFTSAE (p < 0.05). A nomogram containing these four indicators was constructed, and the predictive performance of the nomogram was evaluated using the ROC curve. The AUC of the model was 0.846 (95% confidence interval [CI]: 0.770-0.921), which had good predictive ability for SFTSAE.

CONCLUSION

Conclusion: The overall mortality rate of SFTS patients was 17.53%, and the mortality rate of encephalitis patients was 50%. Old age, high C-reactive protein, elevated d-dimer, and high viral load were independent risk factors for SFTSAE. The nomogram constructed based on these four indicators had good predictive ability and could be used as an evaluation tool for clinical treatment.

Dyslipidemia in severe fever with thrombocytopenia syndrome patients: A retrospective cohort study

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a rapidly progressive infectious disease triggered by a novel bunyavirus (SFTSV). Despite the critical role of host lipid metabolism in viral infections, research on dyslipidemia in SFTS remains limited.

METHODS

This retrospective study included 433 SFTS patients, who were stratified into survival group (n = 365) and death group (n = 68) and who were treated at the Shandong Public Health Clinical Center from September 2021 to December 2023. Additionally, 96 healthy controls with matching baseline characteristics were included from Shandong Provincial Hospital. Cross-sectional analysis based on admission data and longitudinal analysis over time were employed to survey the correlation between serum lipid profiles and mortality in SFTS patients.

RESULTS

SFTS patients exhibited elevated triglyceride (TG) levels and reduced total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) levels compared to healthy individuals. Cross-sectional analysis demonstrated that lower LDL-C and apolipoprotein-B (ApoB) levels were related to elevated mortality risk in SFTS patients. Longitudinal analysis demonstrated that LDL-C and ApoB levels remained consistently lower in the death group, while TG levels gradually declined, and HDL-C levels gradually increased as the disease progressed.

CONCLUSION

SFTS patients exhibit significant dyslipidemia compared to healthy individuals. Lower LDL-C and ApoB levels may independently influence mortality in SFTS patients. Elevated TG and reduced HDL-C levels may associate with disease progression.

Identification of severe fever with thrombocytopenia syndrome virus isolates in the northwest of Hubei Province, China

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne viral disease that is increasingly affecting human being worldwide. The clinical manifestations and mortality rates of SFTS can vary depending on the geographic region and the specific genotype of the SFTS virus (SFTSV). From July 2022 to August 2023, we collected serum samples from 83 patients with suspected SFTSV infection in the northwest of Hubei Province, China. From which, 13 patients tested positive for SFTSV. Phylogenetic analysis of the SFTSV L, M, and S gene segments was performed using the maximum likelihood method to determine the genetic diversity of the isolates. At least 2 SFTSV genotypes (A and F) were identified in the northwest of Hubei Province. The clinical manifestations and laboratory findings on the first day of admission were investigated. Results showed that bleeding and disturbance of consciousness, and significant elevated AST and APTT, are valuable for assessing the prognosis for SFTS patients. This study disclosed the genomic sequences and genotypes of SFTSV spreading in the northwest of Hubei Province for the first time, providing information of genetically etiology for SFTS in the local district. Furthermore, certain symptoms and/or laboratory findings may indicate adverse clinical outcomes, highlighting the importance of identifying the symptoms and monitoring specific laboratory markers. Future research is needed to investigate the threshold values of these markers and to closely observe the indicative symptoms in order to early identify and timely management of critically ill patients within clinical settings.

A Case of Severe Fever with Thrombocytopenia Syndrome and Acute Gastric Mucosal Lesions Confirmed Using Esophagogastroduodenoscopy

Severe fever with thrombocytopenia syndrome (SFTS) is known to cause gastrointestinal hemorrhaging; however, few reports have so far specified the site of the hemorrhaging or lesion characteristics. A 79-year-old man was admitted to the hospital with fever, anorexia, and diarrhea which was suspected to be due to gastroenteritis. On day 2, the patient developed hematemesis. Esophagogastroduodenoscopy revealed an acute gastric mucosal lesion. Further physical examination revealed an eschar, and the blood test was positive for SFTS virus nucleic acid. This case suggests that SFTS-associated gastrointestinal hemorrhage may be caused by acute gastritis. SFTS should therefore be considered in cases with fever, gastrointestinal symptoms, and thrombocytopenia.

Intravenous immunoglobulin‑based adjuvant therapy for severe fever with thrombocytopenia syndrome: A single‑center retrospective cohort study

Intravenous immunoglobulin (IVIG) is frequently administered to patients with severe fever with thrombocytopenia syndrome (SFTS), particularly those with severe manifestations, although its efficacy remains controversial. The study retrospectively analyzed the effects of IVIG administration on SFTS patients in both mild and severe groups. The primary outcome measure was 28-day mortality. Inverse probability of treatment weighting (IPTW) with propensity score was used to account for baseline confounders. A total of SFTS patients with complete data enrolled from January 1, 2015, to August 1, 2023. Death at 28 days occurred for 68 (17.5%) patients. By unadjusted analysis, no difference was observed for 28-day mortality between the IVIG and non-IVIG groups in both the mild and severe groups. Similar results were found by propensity score matching and by IPTW analysis. Although IVIG is frequently used as adjuvant therapy for severe SFTS patients, no significant association was observed between IVIG treatment and reduced mortality in this patient population.

Development and validation of a clinical and laboratory-based nomogram to predict mortality in patients with severe fever with thrombocytopenia syndrome

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging global infectious disease with a high mortality rate. Clinicians lack a convenient tool for early identification of critically ill SFTS patients. The aim of this study was to construct a simple and accurate nomogarm to predict the prognosis of SFTS patients.

METHODS

We retrospectively analyzed the clinical data of 372 SFTS patients collected between May 2015 and June 2023, which were divided 7:3 into a training set and an internal validation set. We used LASSO regression to select predictor variables and multivariable logistic regression to identify independent predictor variables. Prognostic nomograms for SFTS were constructed based on these factors and analysed for concordance index, calibration curves and area under the curve (AUC) to determine the predictive accuracy and consistency of the model.

RESULTS

In the training set, LASSO and multivariate logistic regression analyses showed that age, SFTSV RNA, maximum body temperature, pancreatitis, gastrointestinal bleeding, pulmonary fungal infection (PFI), BUN, and PT were independent risk factors for death in SFTS patients. There was a strong correlation between neurological symptoms and mortality (P < 0.001, OR = 108.92). Excluding neurological symptoms, nomograms constructed based on the other eight variables had AUCs of 0.937 and 0.943 for the training and validation sets, respectively. Furthermore, we found that age, gastrointestinal bleeding, PFI, bacteraemia, SFTSV RNA, platelets, and PT were the independent risk factors for neurological symptoms, with SFTSV RNA having the highest diagnostic value (AUC = 0.785).

CONCLUSIONS

The nomogram constructed on the basis of eight common clinical variables can easily and accurately predict the prognosis of SFTS patients. Moreover, the diagnostic value of neurological symptoms far exceeded that of other predictors, and SFTSV RNA was the strongest independent risk factor for neurological symptoms, but these need to be further verified by external data.

Establishment and validation of a prognostic nomogram for severe fever with thrombocytopenia syndrome: A retrospective observational study

BACKGROUND

Several scoring systems have been proposed to predict the risk of death due to severe fever with thrombocytopenia syndrome (STFS), but they have limitations. We developed a new prognostic nomogram for STFS-related death and compared its performance with previous scoring systems and the Acute Physiology and Chronic Health Evaluation score (APACHE II Score).

METHODS

A total of 292 STFS patients were retrospectively enrolled between January 2016 and March 2023. Boruta's algorithm and backward stepwise regression were used to select variables for constructing the nomogram. Time-dependent receiver operating characteristic (ROC) curves and clinical decision curves were generated to compare the strengths of the nomogram with others.

RESULTS

Age, Sequential Organ Failure Assessment Score (SOFA score), state of consciousness, continuous renal replacement therapy (CRRT), and D-dimer were significantly correlated with mortality in both univariate and multivariate analyses (P<0.05). We developed a nomogram using these variables to predict mortality risk, which outperformed the SFTS and APACHE II scores (Training ROC: 0.929 vs. 0.848 vs. 0.792; Validation ROC: 0.938 vs. 0.839 vs. 0.851; P<0.001). In the validation set, the SFTS model achieved an accuracy of 76.14%, a sensitivity of 95.31%, a specificity of 25.00%, a precision of 77.22%, and an F1 score of 85.32%. The nomogram showed a superior performance with an accuracy of 86.36%, a precision of 88.24%, a recall of 93.75%, and an F1 score of 90.91%.

CONCLUSION

Age, consciousness, SOFA Score, CRRT, and D-Dimer are independent risk factors for STFS-related death. The nomogram based on these factors has an excellent performance in predicting STFS-related death and is recommended for clinical practice.

Impact of Glucocorticoid Therapy on 28-Day Mortality in Patients Having Severe Fever with Thrombocytopenia Syndrome in an Intensive Care Unit: A Retrospective Analysis

Purpose

The high mortality rate associated with the critical stages of severe fever with thrombocytopenia syndrome (SFTS) does not have effective treatment. We aimed to evaluate the 28-day mortality and potential impact of glucocorticoid therapy in these patients.

Patients and Methods

This retrospective observational study included participants from the intensive care unit between July 2019 and April 2023. The participants were categorized into glucocorticoid (GC) and non-GC groups. Propensity score matching (PSM) was employed to ensure comparability between groups. We used Cox proportional hazard models to examine mortality risk associated with GC use, Kaplan-Meier survival analyses for overall survival, stratified Cox proportional hazard models for subgroup analyses, and likelihood ratio tests to examine interactions between subgroups.

Results

Of 218 patients with SFTS (median age, 71 years; male, 49.1%), 61.9% required mechanical ventilation, 58.3% received GC treatment, and the 28-day mortality rate was 61.5%. After PSM, there were 58 patients in each group; post-PSM analysis revealed improved 28-day mortality rates with GC treatment, particularly for patients with Glasgow coma scale (GCS) score <13 (hazard ratio [HR], 95% confidence interval [CI] for GCS score: 9-12: 0.39, 0.17-0.88, p=0.024 and for GCS score: 3-8: 0.09, 0.02-0.35, p=0.001); lactate levels >2 mmol/L (0.35, 0.15-0.83, p=0.017); and norepinephrine usage (0.26, 0.13-0.49, p<0.001). Combining antiviral (0.41, 0.22-0.78, p=0.006) or immunoglobulin therapy (0.22, 0.1-0.51, p<0.001) with GC treatment significantly decreased the 28-day mortality rates, compared with GC monotherapy.

Conclusion

Using GCs reduced the high 28-day mortality rate in the patients, especially with low GCS score, high lactate levels, norepinephrine intake, and on antiviral or immunoglobulin therapy.

Serum lipidome reveals lipid metabolic dysregulation in severe fever with thrombocytopenia syndrome

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a rapidly progressing infectious disease with a high fatality rate caused by a novel bunyavirus (SFTSV). The role of lipids in viral infections is well-documented; however, the specific alterations in lipid metabolism during SFTSV infection remain elusive. This study aims to elucidate the lipid metabolic dysregulations in the early stages of SFTS patients.

METHODS

This study prospectively collected peripheral blood sera from 11 critical SFTS patients, 37 mild SFTS patients, and 23 healthy controls during the early stages of infection for lipidomics analysis. A systematic bioinformatics analysis was conducted from three aspects integrating lipid differential expressions, lipid differential correlations, and lipid-clinical indices correlations to reveal the serum lipid metabolic dysregulation in SFTSV-infected individuals.

RESULTS

Our findings reveal significant lipid metabolic dysregulation in SFTS patients. Specifically, compared to healthy controls, SFTS patients exhibited three distinct modes of lipid differential expression: increased levels of lipids including phosphatidylserine (PS), hexosylceramide (HexCer), and triglycerides (TG); decreased levels of lipids including lysophosphatidylcholine (LPC), acylcarnitine (AcCa), and cholesterol esters (ChE); and lipids showing "dual changes" including phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Finally, based on lipid metabolic pathways and literature analysis, we systematically elucidated the potential mechanisms underlying lipid metabolic dysregulation in the early stage of SFTSV infection.

CONCLUSIONS

Our study presents the first global serum lipidome profile and reveals the lipid metabolic dysregulation patterns in the early stage of SFTSV infection. These findings provide a new basis for the diagnosis, treatment, and further investigation of the disease.

Taurolithocholic acid protects against viral haemorrhagic fever via inhibition of ferroptosis

Bile acids are microbial metabolites that can impact infection of enteric and hepatitis viruses, but their functions during systemic viral infection remain unclear. Here we show that elevated levels of the secondary bile acid taurolithocholic acid (TLCA) are associated with reduced fatality rates and suppressed viraemia in patients infected with severe fever with thrombocytopenia syndrome virus (SFTSV), an emerging tick-borne haemorrhagic fever virus. TLCA inhibits viral replication and mitigates host inflammation during SFTSV infection in vitro, and indirectly suppresses SFTSV-mediated induction of ferroptosis by upregulating fatty acid desaturase 2 via the TGR5-PI3K/AKT-SREBP2 axis. High iron and ferritin serum levels during early infection were correlated with decreased TLCA levels and fatal outcomes in SFTSV-infected patients, indicating potential biomarkers. Furthermore, treatment with either ferroptosis inhibitors or TLCA protected mice from lethal SFTSV infection. Our findings highlight the therapeutic potential of bile acids to treat haemorrhagic fever viral infection.

The Association Between Elevated Myocardial Injury-Related Biomarker (TnI) and Increased Mortality in Patients With Severe Fever With Thrombocytopenia Syndrome

OBJECTIVES

The objective of this study was to investigate the dynamic profiles of myocardial injury biomarkers and their association with mortality in patients with severe fever with thrombocytopenia syndrome (SFTS).

DESIGN

A retrospective cohort study.

SETTINGS

Union Hospital in Wuhan, China.

PATIENTS

A total of 580 patients with SFTS, observed between May 2014 and December 2021, were included in the final analysis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

In total, 580 patients with SFTS were enrolled in the study, comprised of 469 survivors and 111 nonsurvivors, with a 21-day fatality rate of 19.1%. The elevation of troponin I (TnI) was observed in 61.6% patients (357/580) with SFTS upon admission, and 68.4% patients (397/580) developed an abnormal TnI level during hospitalization. Multivariate logistic regression identified age, viral load, platelet count, creatinine level, and TnI level as potential risk factors for mortality in patients with SFTS. The results of restricted cubic splines revealed that when the TnI level (baseline TnI: 1.55 [lg (ng/L+1)], peak value: TnI 1.90 [lg (ng/L+1)]) exceeded a certain threshold, the predicted mortality of patients with SFTS increased alongside the rise in TnI levels. Mortality rate surpassed 40% among patients with SFTS with TnI greater than or equal to 10 times the upper limit of normal at admission (43.8%) or during hospitalization (41.7%). Older age, a history of cardiovascular disease, and higher d -dimer levels were potential risk factors for elevated TnI levels in patients with SFTS.

CONCLUSIONS

Elevated TnI levels were prevalent among patients with SFTS and were strongly associated with an increased risk of mortality.

Association of gastrointestinal symptoms with mortality in patients with severe fever with thrombocytopenia syndrome

Background

The clinical significance of gastrointestinal (GI) symptoms in patients with severe fever and thrombocytopenia syndrome (SFTS) is poorly characterized. This study aimed to determine the prevalence and effect of GI symptoms on the prognosis of patients with SFTS.

Methods

This was a retrospective multi-center cohort study that included hospitalized patients with SFTS from three institutions between October 2010 and August 2022. The risk factors for mortality and intensive care unit (ICU) admission were identified by Cox and logistic regression analyses, respectively. Kaplan-Meier curves were used to analyze the cumulative mortality risk.

Results

Among 304 patients, the median age was 62.0 years and 51.0 % of the patients were male. A total of 202 patients (66.4 %) had at least one GI symptom on admission. Diarrhea (69.8 %) and nausea (57.4 %) were the most common symptoms. Patients with GI symptoms had lower male proportion (46.0 % vs. 60.8 %, P = 0.015), higher aspartate aminotransferase (177.5 U/L vs. 118.0 U/L, P = 0.010) and lactic dehydrogenase (771.0 U/L vs. 666.5 U/L, P = 0.017) levels than that of patients without GI symptoms. However, there was no significant difference in mortality rates (23.8 % vs. 21.6 %, P = 0.668) and ICU admission (14.4 % vs. 12.7 %, P = 0.701) between SFTS patients with and without GI symptoms. Multivariate analysis suggested that GI symptoms at admission were not associated with mortality and ICU admission.

Conclusions

GI symptoms are common in patients with SFTS. However, the presence of GI symptoms was not an independent risk factor for poor prognosis.

Identification of CCL20 as a Prognostic Predictor for Severe Fever With Thrombocytopenia Syndrome Based on Plasma Proteomics

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS), a lethal tick-borne hemorrhagic fever, prompted our investigation into prognostic predictors and potential drug targets using plasma Olink Proteomics.

METHODS

Employing the Olink assay, we analyzed 184 plasma proteins in 30 survivors and 8 nonsurvivors of SFTS. Validation was performed in a cohort of 154 patients with SFTS via enzyme-linked immunosorbent assay. We utilized the Drug-Gene Interaction Database to identify protein-drug interactions.

RESULTS

Nonsurvivors exhibited 110 differentially expressed proteins as compared with survivors, with functional enrichment in the cell chemotaxis-related pathway. Thirteen differentially expressed proteins-including C-C motif chemokine 20 (CCL20), calcitonin gene-related peptide alpha, and pleiotrophin-were associated with multiple-organ dysfunction syndrome. CCL20 emerged as the top predictor of death, demonstrating an area under the curve of 1 (P = .0004) and 0.9033 (P < .0001) in the discovery and validation cohorts, respectively. Patients with CCL20 levels exceeding 45.74 pg/mL exhibited a fatality rate of 45.65%, while no deaths occurred in those with lower CCL20 levels. Furthermore, we identified 202 Food and Drug Administration-approved drugs targeting 37 death-related plasma proteins.

CONCLUSIONS

Distinct plasma proteomic profiles characterize SFTS cases with different outcomes, with CCL20 emerging as a novel, sensitive, accurate, and specific biomarker for predicting SFTS prognosis.

Construction and validation of a dynamic nomogram using Lasso-logistic regression for predicting the severity of severe fever with thrombocytopenia syndrome patients at admission

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a highly fatal infectious disease caused by the SFTS virus (SFTSV), posing a significant public health threat. This study aimed to construct a dynamic model for the early identification of SFTS patients at high risk of disease progression.

METHODS

All eligible patients enrolled between April 2014 and July 2023 were divided into training and validation sets. Thirty-four clinical variables in the training set underwent analysis using least absolute shrinkage and selection operator (LASSO) logistic regression. Selected variables were then input into the multivariate logistic regression model to construct a dynamic nomogram. The model's performance was assessed using the area under the receiver operating characteristic curve (AUC-ROC), concordance index (C-index), calibration curve, and decision curve analysis (DCA) in both training and validation sets. Kaplan-Meier survival analysis was utilized to evaluate prognostic performance.

RESULTS

299 SFTS patients entered the final investigation, with 208 patients in the training set and 90 patients in the validation set. LASSO and the multivariate logistic regression identified six significant prediction factors: age (OR, 1.060; 95% CI, 1.017-1.109; P = 0.007), CREA (OR, 1.017; 95% CI, 1.003-1.031; P = 0.019), PT (OR, 1.765; 95% CI, 1.175-2.752; P = 0.008), D-dimer (OR, 1.039; 95% CI, 1.005-1.078; P = 0.032), nervous system symptoms (OR, 8.244; 95% CI, 3.035-26.858; P < 0.001) and hemorrhage symptoms (OR, 3.414; 95% CI, 1.096-10.974; P = 0.035). The AUC-ROC, C-index, calibration plots, and DCA demonstrated the robust performance of the nomogram in predicting severity at admission, and Kaplan-Meier survival analysis indicated its utility in predicting 28-day mortality among SFTS patients. The dynamic nomogram is accessible at https://sfts.shinyapps.io/SFTS_severity_nomogram/ .

CONCLUSION

This study provided a practical and readily applicable tool for the early identification of high-risk SFTS patients, enabling the timely initiation of intensified treatments and protocol adjustments to mitigate disease progression.

Establishment and validation of a clinical risk scoring model to predict fatal risk in SFTS hospitalized patients

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infection with a high case fatality rate. Significant gaps remain in studies analyzing the clinical characteristics of fatal cases.

METHODS

From January 2017 to June 2023, 427 SFTS cases were included in this study. A total of 67 variables about their demographic, clinical, and laboratory data were collected. Univariate logistic regression and the least absolute shrinkage and selection operator (LASSO) method was used to screen predictors from the cohort. Multivariate logistic regression was used to identify independent predictors and nomograms were developed. Calibration, decision curves and area under the curve (AUC) were used to assess model performance.

RESULTS

The multivariate logistic regression analysis screened out the four most significant factors, including age > 70 years (p = 0.001, OR = 2.516, 95% CI 1.452-4.360), elevated serum PT (p < 0.001, OR = 1.383, 95% CI 1.143-1.673), high viral load (p < 0. 001, OR = 1.496, 95% CI 1.290-1.735) and high level of serum urea (> 8.0 μmol/L) (p < 0.001, OR = 4.433, 95% CI 1.888-10.409). The AUC of the nomogram based on these four factors was 0.813 (95% CI, 0.758-0.868). The bootstrap resampling internal validation model performed well, and decision curve analysis indicated a high net benefit.

CONCLUSIONS

The nomogram based on age, elevated PT, high serum urea level, and high viral load can be used to help early identification of SFTS patients at risk of fatality.

Development and Comparison of Time Series Models in Predicting Severe Fever with Thrombocytopenia Syndrome Cases - Hubei Province, China, 2013-2020

Introduction

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by the SFTS virus, which has a high mortality rate. Predicting the number of SFTS cases is essential for early outbreak warning and can offer valuable insights for establishing prevention and control measures.

Methods

In this study, data on monthly SFTS cases in Hubei Province, China, from 2013 to 2020 were collected. Various time series models based on seasonal auto-regressive integrated moving average (SARIMA), Prophet, eXtreme Gradient Boosting (XGBoost), and long short-term memory (LSTM) were developed using these historical data to predict SFTS cases. The established models were evaluated and compared using mean absolute error (MAE) and root mean squared error (RMSE).

Results

Four models were developed and performed well in predicting the trend of SFTS cases. The XGBoost model outperformed the others, yielding the closest fit to the actual case numbers and exhibiting the smallest MAE (2.54) and RMSE (2.89) in capturing the seasonal trend and predicting the monthly number of SFTS cases in Hubei Province.

Conclusion

The developed XGBoost model represents a promising and valuable tool for SFTS prediction and early warning in Hubei Province, China.

Machine learning for identifying risk of death in patients with severe fever with thrombocytopenia syndrome

Background

Severe fever with thrombocytopenia syndrome (SFTS) has attracted attention due to the rising incidence and high severity and mortality rates. This study aims to construct a machine learning (ML) model to identify SFTS patients at high risk of death early in hospital admission, and to provide early intensive intervention with a view to reducing the risk of death.

Methods

Data of patients hospitalized for SFTS in two hospitals were collected as training and validation sets, respectively, and six ML methods were used to construct the models using the screened variables as features. The performance of the models was comprehensively evaluated and the best model was selected for interpretation and development of an online web calculator for application.

Results

A total of 483 participants were enrolled in the study and 96 (19.88%) patients died due to SFTS. After a comprehensive evaluation, the XGBoost-based model performs best: the AUC scores for the training and validation sets are 0.962 and 0.997.

Conclusion

Using ML can be a good way to identify high risk individuals in SFTS patients. We can use this model to identify patients at high risk of death early in their admission and manage them intensively at an early stage.

Clinical factors associated with invasive pulmonary aspergillosis in patients with severe fever with thrombocytopenia syndrome: analysis of a 6-year clinical experience

Background

Invasive pulmonary aspergillosis (IPA) typically occurs in immunocompromised individuals. Severe fever with thrombocytopenia syndrome (SFTS) patients are typically characterized by fever, thrombocytopenia, and leukopenia. These patients typically present with dysregulation of cellular and humoral immunity, which may predispose them to IPA. Our study aimed to identify risk factors for SFTS-associated invasive pulmonary aspergillosis (SAPA) and evaluate its associated prognostic impact.

Methods

We conducted a cohort study between January 2017 and December 2022 in a tertiary hospital in Wuhan City, China. All SFTS patients hospitalized in our department who formally consented were divided into a SAPA group and a non-SAPA group according to whether they were coinfected with aspergillosis or not. The independent risk factors for the SAPA group were determined by multivariate logistic regression. Receiver operating characteristic (ROC) analysis was used to assess the statistical value of parameters to predict SAPA patients. The survival analysis was carried out using the Kaplan-Meier (KM) method.

Results

Of the 269 hospitalized SFTS patients enrolled in the study, 118 (43.87%) cases were diagnosed with SAPA with an average age of 65.71 ± 9.7 years. Multivariate logistic regression analysis revealed that age, neurological complications, serum severe fever with thrombocytopenia syndrome virus (SFTSV) RNA loads, the white blood cell (WBC) count, platelet (PLT) count, albumin (ALB) and globulin (GLB) concentrations, and cardiac troponin I (cTNI) were complementary risk factors for the development of IPA in SFTS patients. The risk score is calculated as 5 times age, plus 6 times neurological complications, plus 10 times RNA (log), plus 5 times WBC, minus 5 times PLT, minus 5 times ALB, plus 5 times GLB, and plus 6 times cTNI. ROC curve analysis showed that the area under the receiver operating characteristic (AUROC) curve represented a risk score of 0.837 (95% CI: 0.789-0.885, p < 0.001) for predicting IPA in SFTS patients. The average length of hospitalization in the SAPA group was more prolonged than non-SAPA. SAPA and non-SAPA groups had significantly different mortality rates: 25.42% (SAPA) and 3.97% (non-SAPA) (p < 0.05).

Conclusion

SFTS patients with IPA have high morbidity and mortality. Early monitoring of neurological complications, SFTSV RNA loads, WBC, PLT, ALB, GLB, and cTNI in SFTS patients may be useful in predicting the occurrence of IPA.

Spatial and Temporal Analysis of Severe Fever with Thrombocytopenia Syndrome in Anhui Province from 2011 to 2023

OBJECTIVE

To analyze the spatial autocorrelation and spatiotemporal clustering characteristics of severe fever with thrombocytopenia syndrome(SFTS) in Anhui Province from 2011 to 2023.

METHODS

Data of SFTS in Anhui Province from 2011 to 2023 were collected. Spatial autocorrelation analysis was conducted using GeoDa software, while spatiotemporal scanning was performed using SaTScan 10.0.1 software to identify significant spatiotemporal clusters of SFTS.

RESULTS

From 2011 to 2023, 5720 SFTS cases were reported in Anhui Province, with an average annual incidence rate of 0.7131/100,000. The incidence of SFTS in Anhui Province reached its peak mainly from April to May, with a small peak in October. The spatial autocorrelation results showed that from 2011 to 2023, there was a spatial positive correlation(P < 0.05) in the incidence of SFTS in all counties and districts of Anhui Province. Local autocorrelation high-high clustering areas are mainly located in the south of the Huaihe River. The spatiotemporal scanning results show three main clusters of SFTS in recent years: the first cluster located in the lower reaches of the Yangtze River, the eastern region of Anhui Province; the second cluster primarily focused on the region of the Dabie Mountain range, while the third cluster primarily focused on the region of the Huang Mountain range.

CONCLUSIONS

The incidence of SFTS in Anhui Province in 2011-2023 was spatially clustered.

A nomogram and heat map based on LASSO-Cox regression for predicting the risk of early-stage severe fever with thrombocytopenia syndrome patients developing into critical illness at 7-day and 14-day

Severe fever with thrombocytopenia syndrome (SFTS) represents an emerging infectious disease characterized by a substantial mortality risk. Early identification of patients is crucial for effective risk assessment and timely interventions. In the present study, least absolute shrinkage and selection operator (LASSO)-Cox regression analysis was conducted to identify key risk factors associated with progression to critical illness at 7-day and 14-day. A nomogram was constructed and subsequently assessed for its predictive accuracy through evaluation and validation processes. The risk stratification of patients was performed using X-tile software. The performance of this risk stratification system was assessed using the Kaplan-Meier method. Additionally, a heat map was generated to visualize the results of these analyses. A total of 262 SFTS patients were included in this study, and four predictive factors were included in the nomogram, namely viral copies, aspartate aminotransferase (AST) level, C-reactive protein (CRP), and neurological symptoms. The AUCs for 7-day and 14-day were 0.802 [95% confidence interval (CI): 0.707-0.897] and 0.859 (95% CI: 0.794-0.925), respectively. The nomogram demonstrated good discrimination among low, moderate, and high-risk groups. The heat map effectively illustrated the relationships between risk groups and predictive factors, providing valuable insights with high predictive and practical significance.

Ecological Changes Exacerbating the Spread of Invasive Ticks has Driven the Dispersal of Severe Fever with Thrombocytopenia Syndrome Virus Throughout Southeast Asia

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne virus recognized by the World Health Organization as an emerging infectious disease of growing concern. Utilizing phylodynamic and phylogeographic methods, we have reconstructed the origin and transmission patterns of SFTSV lineages and the roles demographic, ecological, and climatic factors have played in shaping its emergence and spread throughout Asia. Environmental changes and fluctuations in tick populations, exacerbated by the widespread use of pesticides, have contributed significantly to its geographic expansion. The increased adaptability of Lineage L2 strains to the Haemaphysalis longicornis vector has facilitated the dispersal of SFTSV through Southeast Asia. Increased surveillance and proactive measures are needed to prevent further spread to Australia, Indonesia, and North America.

Activation of neurotoxic A1-reactive astrocytes by SFTS virus infection accelerates fatal brain damage in IFNAR1-/- mice

Severe fever with thrombocytopenia syndrome (SFTS) has a high mortality rate compared to other infectious diseases. SFTS is particularly associated with a high risk of mortality in immunocompromised individuals, while most patients who die of SFTS exhibit symptoms of severe encephalitis before death. However, the region of brain damage and mechanisms by which the SFTS virus (SFTSV) causes encephalitis remains unknown. Here, we revealed that SFTSV infects the brainstem and spinal cord, which are regions of the brain associated with respiratory function, and motor nerves in IFNAR1-/- mice. Further, we show that A1-reactive astrocytes are activated, causing nerve cell death, in infected mice. Primary astrocytes of SFTSV-infected IFNAR1-/- mice also induced neuronal cell death through the activation of A1-reactive astrocytes. Herein, we showed that SFTSV induces fatal neuroinflammation in the brain regions important for respiratory function and motor nerve, which may underlie mortality in SFTS patients. This study provides new insights for the treatment of SFTS, for which there is currently no therapeutic approach.

Analysis of early warning indicators of death in patients with severe fever with thrombocytopenia syndrome

BACKGROUND

Since its discovery, severe fever with thrombocytopenia syndrome (SFTS) has been characterized by rapid progression and poor prognosis, and no specific treatment is available. The aim of this study was to investigate the early warning indicators of mortality in SFTS patients.

METHODS

This is a retrospective cross-sectional study. The study subjects were patients who were admitted to the hospital with a confirmed diagnosis of SFTS from January 2023 to October 2023, and their clinical symptoms and signs at the time of admission, as well as the laboratory indexes of the first blood collection after admission were collected, grouped according to the prognosis, and statistically analyzed.

RESULTS

A total of 141 patients were collected, of which 27 patients died and 114 patients were in the survival group. Through statistical analysis, patients with combined hemorrhagic manifestations, disturbance of consciousness, lymphopenia, elevated lipase, and prolonged thrombin time on admission were independent risk factors for patients' death. By plotting the working characteristic curve of the subjects, as well as calculating the area under the curve, the results showed that the AUC of lymphopenia count was 0.670, 95% CI (0.563-0.776), P = 0.006; the AUC of elevated serum lipase index was 0.789, 95% CI (0.699-0.878), p < 0.001; the AUC of prolonged thrombin time was 0.749, 95% CI (0.645-0.854), p < 0.001.

CONCLUSION

Patients with hemorrhagic manifestations, disturbance of consciousness, lymphocyte reduction, elevated serum lipase, and prolonged thrombin time on admission are more worthy of the clinician's attention, and require early and effective interventions to avoid further disease progression.

Development and validation of the PLNA score to predict cytokine storm in acute-phase SFTS patients: A single-center cohort study

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease known for its high mortality rate and its correlation with Cytokine Storms (CS). Timely detection of CS is crucial for improving the prognosis of the disease. The objective of this investigation was to develop a model for identifying cytokine storms in the acute phase of SFTS.

METHODS

A total of 245 patients diagnosed with SFTS were included in this study between January 2020 and July 2022. Among them, 184 patients were part of the training set, while 61 patients were part of the validation set. Variables identified by LASSO were subsequently included in a multivariate logistic regression analysis to determine independent predictors. Subsequently, a nomogram was then developed to predict the likelihood of CS in SFTS patients. The predictive efficacy and clinical applicability of the nomogram model were further assessed through ROC analysis and the DCA curve.

RESULTS

Following LASSO analysis, a total of 11 indicators were included in multivariate logistic regression analysis. The findings indicated that PLT (OR 0.865, P < 0.001), LDH (OR 1.002, P < 0.001), Na+ (OR 1.155, P = 0.005), and ALT (OR 1.019, P < 0.001) serve as independently predictors of CS in the acute phase of SFTS. Furthermore, a nomogram named the PLNA was constructed by integrating these four factors. The PLNA model exhibited favorable predictive accuracy with an AUC of 0.958. Moreover, the PLNA model exhibited excellent clinical applicability in both the training and validation sets, as evidenced by the DCA curve.

CONCLUSIONS

The PLNA model, constructed using clinical indicators, can predict the probability of cytokine storm in the acute phase of SFTS patients.

The differences in cytokine signatures between severe fever with thrombocytopenia syndrome (SFTS) and hemorrhagic fever with renal syndrome (HFRS)

Severe fever with thrombocytopenia syndrome (SFTS) virus and hantavirus are categorized under the Bunyavirales order. The severe disease progression in both SFTS and hemorrhagic fever with renal syndrome (HFRS) is associated with cytokine storms. This study aimed to explore the differences in cytokine profiles and immune responses between the two diseases. A cross-sectional, single-center study involved 100 participants, comprising 46 SFTS patients, 48 HFRS patients, and 6 healthy controls. The study employed the Luminex cytokine detection platform to measure 48 cytokines. The differences in cytokine profiles and immune characteristics between the two diseases were further analyzed using multiple linear regression, principal component analysis, and random forest method. Among the 48 cytokines tested, 30 showed elevated levels in SFTS and/or HFRS compared to the healthy control group. Furthermore, there were 19 cytokines that exhibited significant differences between SFTS and HFRS. Random forest analysis suggested that TRAIL and CTACK were predictive of SFTS, while IL2Ralpha, MIG, IL-8, IFNalpha2, HGF, SCF, MCP-3, and PDGFBB were more common with HFRS. It was further verified by the receiver operating characteristic with area under the curve >0.8 and P-values <0.05, except for TRAIL. Significant differences were observed in the cytokine profiles of SFTS and HFRS, with TRAIL, IL2Ralpha, MIG, and IL-8 being the top 4 cytokines that most clearly distinguished the two diseases.

IMPORTANCE

SFTS and HFRS differ in terms of cytokine immune characteristics. TRAIL, IL-2Ralpha, MIG, and IL-8 were the top 4 that differed markedly between SFTS and HFRS.

Red Blood Cell Distribution Width Predicts Mortality in Hospitalized Patients with Severe Fever with Thrombocytopenia Syndrome

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging epidemic infectious disease with high mortality rate. This study aimed to investigate the association of red blood cell distribution width (RDW) and mortality risk in hospitalized SFTS patients.

Methods

Clinical data of SFTS patients was retrospectively collected from three hospitals between October 2010 and August 2022. Cox proportional hazards model was used to identity the risk factors for fatal outcome. The predictive value of RDW for fatal outcome was evaluated by the receiver operating characteristic (ROC) analysis and Kaplan-Meier methods.

Results

Of 292 patients, the median age was 61.5 years. Non-survivors showed higher RDW value than survivors (13.6% vs.13.0%, P < 0.001). The mortality rate was 44.8% in patients with elevated RDW compared to 18.4% of patients with normal RDW, with a relative risk (RR) of 2.439. Elevated RDW was an independent risk factor of mortality (hazards ratio: 1.167, P = 0.019). Patients with elevated RDW had a higher cumulative mortality than patients with normal RDW. The area under the ROC curve (AUC) of RDW for the prediction of mortality was 0.690 (P < 0.001).

Conclusion

Elevated RDW was associated with higher mortality risk for patients hospitalized for SFTS. RDW may be helpful for risk stratification in SFTS patients.

Viral shedding pattern of severe fever with thrombocytopenia syndrome virus in severely ill patients: A prospective, Multicenter cohort study

Background

Severe fever with thrombocytopenia syndrome (SFTS) is spreading rapidly in Asia. The pathway of SFTS virus shedding from patient and specific use of personal protective equipments (PPEs) against viral transmission have rarely been reported. The study was to determine SFTS virus (SFTSV) shedding pattern from the respiratory, digestive and urinary tract to outside in patients. Methods: Patients were divided into mild and severe groups in three sentinel hospitals for SFTS in Anhui province from April 2020 to October 2022. SFTSV level from blood, throat swabs, fecal/anal swabs, urine and bedside environment swabs of SFTS patients were detected by qRT-PCR. Specific PPEs were applied in healthcare workers contacting with the patients who had oropharyngeal virus shedding and hemorrhagic signs.

Results

A total of 189 SFTSV-confirmed patients were included in the study, 54 patients died (case fatality rate, 28.57 %). Positive SFTSV in throat swabs (T-SFTSV), fecal/anal swabs (F-SFTSV) and urine (U-SFTSV) were detected in 121 (64.02 %), 91 (48.15 %) and 65 (34.4 %) severely ill patients, respectively. The levels of T-SFTSV, F-SFTSV and U-SFTSV were positively correlated with the load of SFTSV in blood. We firstly revealed that SFTSV positive rate of throat swabs were correlated with occurrence of pneumonia and case fatality rate of patients (P < 0.0001). Specific precaution measures were applied by healthcare workers in participating cardiopulmonary resuscitation and orotracheal intubation for severely ill patients with positive T-SFTSV, no event of SFTSV human-to-human transmission occurred after application of effective PPEs.

Conclusions

Our research demonstrated SFTSV could shed out from blood, oropharynx, feces and urine in severely ill patients. The excretion of SFTSV from these parts was positively correlated with viral load in the blood. Effective prevention measures against SFTSV human-to-human transmission are needed.

Global epidemiology of severe fever with thrombocytopenia syndrome virus in human and animals: a systematic review and meta-analysis

Background

Since the initial identification of the Severe Fever with Thrombocytopenia Syndrome (SFTS) in ticks in rural areas of China in 2009, the virus has been increasingly isolated from a diverse array of hosts globally, exhibiting a rising trend in incidence. This study aims to conduct a systematic analysis of the temporal and spatial distribution of SFTS cases, alongside an examination of the infection rates across various hosts, with the objective of addressing public concerns regarding the spread and impact of the disease.

Methods

In this systematic review and meta-analysis, an exhaustive search was conducted across multiple databases, including PubMed, Web of Science, Embase, and Medline, CNKI, WanFang, and CQVIP. The literature search was confined to publications released between January 1, 2009, and May 29, 2023. The study focused on collating data pertaining to animal infections under natural conditions and human infection cases reported. Additionally, species names were unified using the National Center for Biotechnology Information (NCBI) database. The notification rate, notification death rate, case fatality rate, and infection rates (or MIR) were assessed for each study with available data. The proportions were pooled using a generalized linear mixed-effects model (GLMM). Meta-regressions were conducted for subgroup analysis. This research has been duly registered with PROSPERO, bearing the registration number CRD42023431010.

Findings

We identified 5492 studies from database searches and assessed 238 full-text studies for eligibility, of which 234 studies were included in the meta-analysis. For human infection data, the overall pooled notification rate was 18.93 (95% CI 17.02-21.05) per ten million people, the overall pooled notification deaths rate was 3.49 (95% CI 2.97-4.10) per ten million people, and the overall pooled case fatality rate was 7.80% (95% CI 7.01%-8.69%). There was an increasing trend in notification rate and deaths rate, while the case fatality rate showed a significant decrease globally. Regarding animal infection data, among 94 species tested, 48 species were found to carry positive nucleic acid or antibodies. Out of these, 14 species were classified under Arthropoda, while 34 species fell under Chordata, comprising 27 Mammalia and 7 Aves.

Interpretation

This systematic review and meta-analysis present the latest global report on SFTS. In terms of human infections, notification rates and notification deaths rates are on the rise, while the case fatality rate has significantly decreased. More SFTSV animal hosts have been discovered than before, particularly among birds, indicating a potentially broader transmission range for SFTSV. These findings provide crucial insights for the prevention and control of SFTS on a global scale.

Funding

None.

Effect of tocilizumab plus corticosteroid on clinical outcome in patients hospitalized with severe fever with thrombocytopenia syndrome: A randomized clinical trial

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging viral hemorrhagic fever with high fatality rates. The blockade of pro-inflammatory cytokines presents a promising therapeutic strategy.

METHODS

We conducted a randomized clinical trial at the 154th hospital, Xinyang, Henan Province. Eligible patients with severe SFTS disease were randomly assigned in a 1:2 ratio to receive either a single intravenous infusion of tocilizumab plus usual care; or usual care only. The primary outcome was the clinical status of death/survival at day 14, while secondary outcomes included improvement from baseline in liver and kidney damage and time required for hospital discharge. The efficacy of tocilizumab plus corticosteroid was compared to those receiving corticosteroid alone. The trial is registered with the Chinese Clinical Trial Registry website (ChiCTR2300076317).

RESULTS

63 eligible patients were assigned to the tocilizumab group and 126 to the control group. The addition of tocilizumab to usual care was associated with a reduced death rate (9.5%) compared to those received only usual care (23.0%), with an adjusted hazard ratio (aHR) of 0.37 (95% confidence interval [CI], 0.15 to 0.91, P = 0.029). Combination therapy of tocilizumab and corticosteroids was associated with a significantly reduced fatality (aHR, 0.21; 95% CI, 0.08 to 0.56; P = 0.002) compared to those receiving corticosteroids alone.

CONCLUSIONS

A significant benefit of reducing fatality in severe SFTS patients was observed by using tocilizumab. A combined therapy of tocilizumab plus corticosteroids was recommended for the therapy of severe SFTS.

Lower serum LDL-C levels are associated with poor prognosis in severe fever with thrombocytopenia syndrome: a single-center retrospective cohort study

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease triggered by a novel bunyavirus (SFTSV). Characterized by fever, thrombocytopenia, leukocytopenia, and multiple organ dysfunction manifestations, its primary mode of transmission is through tick bites. Despite the critical role of lipid metabolism in viral infections, the role of lipids in SFTS remains unclear.

Methods

This retrospective study analyzed 602 patients with SFTS treated at the Shandong Public Health Clinical Center from January 2021 to December 2023. Based on the endpoint events, patients were classified into survival (S) and death (D) groups. The S group was further classified into non-critical (non-C) and critical (C) groups based on symptoms. All patients were followed up for at least 28 days after admission. Propensity score matching, multivariable logistic regression, survival analysis, time trend analysis, and mediation analysis were conducted to assess the association between LDL-C levels and prognosis in SFTS.

Results

The serum LDL-C levels on admission were significantly lower in the D and C groups than in the S and non-C groups. The logistic regression models indicated a potential association between LDL-C levels and a poor prognosis in SFTS. The restricted cubic spline showed a unidirectional trend between LDL-C levels and mortality, with a cutoff value of 1.59 mmol/L. The survival analysis revealed higher and earlier mortality in the low-LDL-C group than in the high-LDL-C group. The trends over 28 days post-admission showed that the serum LDL-C levels gradually increased in SFTS, with a favorable prognosis. Finally, the mediation analysis indicated that low LDL-C levels are associated with mortality through poor hepatic, cardiac, and coagulation functions.

Conclusion

Low LDL-C levels are potentially associated with a poor prognosis in SFTS.

Activated partial thromboplastin time predicts mortality in patients with severe fever with thrombocytopenia syndrome: A multicenter study in north China

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with high lethality. This study aimed to determine whether prolonged activated partial thromboplastin time (APTT) predicted SFTS mortality.

Methods

SFTS patients were enrolled from 6 hospitals in the north China. Subjects were divided into training cohort and 5 externally validation cohorts. The least absolute shrinkage and selection operator Cox regression model was performed to screen potential prognostic factors. Risk factors were analyzed using multivariable regression models. Prognostic models were established by Cox regression and random survival forest (RSF) methods, and evaluated regarding discrimination, validity and clinical benefit. Time-dependent receiver operating characteristic (ROC) curve was used to evaluate the predictive effectiveness of variables.

Results

1332 SFTS cases were included, in which 211 patients died. Six potential prognostic factors were screened, and pulse, breath, APTT and aspartic transaminase (AST) were independently associated with mortality in both training cohort (Yantai, N = 791) and external validation cohort (N = 541). APTT was steadily correlated with the fatality (HR: 1.039-1.144; all P < 0.01) in each five sub-validation cohorts (Dandong, Dalian, Tai'an, Qingdao and Beijing). RSF model with variables of APTT, AST, pulse and breath had considerable prognostic effectiveness, which APTT showed the highest prognostic ability with the area under the curve of 0.848 and 0.787 for 7-day and 14-day survival, respectively. Survival differences were found between high and low levels of APTT for mortality using 50s as the optimal cut-off.

Conclusions

SFTS patients have prolonged APTT, which is an independent risk factor for fatality. APTT≥50s was recommended as a biomarker to remind physicians to monitor and treat patients more aggressively to improve clinical prognosis.

SFTSV nucleoprotein mediates DNA sensor cGAS degradation to suppress cGAS-dependent antiviral responses

Cyclic GMP-AMP synthase (cGAS) is an important DNA pattern recognition receptor that senses double-stranded DNA derived from invading pathogens or self DNA in cytoplasm, leading to an antiviral interferon response. A tick-borne Bunyavirus, severe fever with thrombocytopenia syndrome virus (SFTSV), is an RNA virus that causes a severe emerging viral hemorrhagic fever in Asia with a high case fatality rate of up to 30%. However, it is unclear whether cGAS interacts with SFTSV infection. In this study, we found that SFTSV infection upregulated cGAS RNA transcription and protein expression, indicating that cGAS is an important innate immune response against SFTSV infection. The mechanism of cGAS recognizing SFTSV is by cGAS interacting with misplaced mitochondrial DNA in the cytoplasm. Depletion of mitochondrial DNA significantly inhibited cGAS activation under SFTSV infection. Strikingly, we found that SFTSV nucleoprotein (N) induced cGAS degradation in a dose-dependent manner. Mechanically, N interacted with the 161-382 domain of cGAS and linked the cGAS to LC3. The cGAS-N-LC3 trimer was targeted to N-induced autophagy, and the cGAS was degraded in autolysosome. Taken together, our study discovered a novel antagonistic mechanism of RNA viruses, SFTSV is able to suppress the cGAS-dependent antiviral innate immune responses through N-hijacking cGAS into N-induced autophagy. Our results indicated that SFTSV N is an important virulence factor of SFTSV in mediating host antiviral immune responses.

IMPORTANCE

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne RNA virus that is widespread in East and Southeast Asian countries with a high fatality rate of up to 30%. Up to now, many cytoplasmic pattern recognition receptors, such as RIG-I, MDA5, and SAFA, have been reported to recognize SFTSV genomic RNA and trigger interferon-dependent antiviral responses. However, current knowledge is not clear whether SFTSV can be recognized by DNA sensor cyclic GMP-AMP synthase (cGAS). Our study demonstrated that cGAS could recognize SFTSV infection via ectopic mitochondrial DNA, and the activated cGAS-stimulator of interferon genes signaling pathway could significantly inhibit SFTSV replication. Importantly, we further uncovered a novel mechanism of SFTSV to inhibit innate immune responses by the degradation of cGAS. cGAS was degraded in N-induced autophagy. Collectively, this study illustrated a novel virulence factor of SFTSV to suppress innate immune responses through autophagy-dependent cGAS degradation.