Human Metapneumovirus Infections Following Hematopoietic Cell Transplantation: Factors Associated With Disease Progression

Effects of long-term corticosteroid use on susceptibility to respiratory viruses: a narrative review

BACKGROUND

Synthetic glucocorticoids are among the most commonly administered drugs due to their potent immunomodulatory properties. However, they may put patients at risk for infections. Their effect on the incidence of respiratory viral infections (RVIs) remains unclear.

OBJECTIVES

The aim of this review is to provide an insightful overview of the most up-to-date evidence regarding the extent to which the use of corticosteroids (CSs) influences the risk of RVIs.

SOURCES

The PubMed database was searched for studies on the association between CSs and RVIs from inception until 15 December 2023.

CONTENT

CSs have differing impacts on the risk of RVIs in asthma and chronic obstructive pulmonary disease, influenced by both the specific virus and the type and dose of CSs. Furthermore, current data demonstrate that CSs may increase the risk of RVIs in patients with systemic lupus erythematosus, rheumatoid arthritis, vasculitis, solid tumours, haematological malignancies, and among transplant recipients.

IMPLICATIONS

Large-scale studies are imperative to inform a more accurate and personalized risk stratification for RVIs. This, in turn, will point towards new strategies for RVI prevention and associated morbidity and mortality in high-risk populations.

Upper and/or Lower Respiratory Tract Infection Caused by Human Metapneumovirus After Allogeneic Hematopoietic Stem Cell Transplantation

BACKGROUND

Human metapneumovirus (hMPV) epidemiology, clinical characteristics and risk factors for poor outcome after allogeneic stem cell transplantation (allo-HCT) remain a poorly investigated area.

METHODS

This retrospective multicenter cohort study examined the epidemiology, clinical characteristics, and risk factors for poor outcomes associated with human metapneumovirus (hMPV) infections in recipients of allo-HCT.

RESULTS

We included 428 allo-HCT recipients who developed 438 hMPV infection episodes between January 2012 and January 2019. Most recipients were adults (93%). hMPV infections were diagnosed at a median of 373 days after allo-HCT. The infections were categorized as upper respiratory tract disease (URTD) or lower respiratory tract disease (LRTD), with 60% and 40% of cases, respectively. Patients with hMPV LRTD experienced the infection earlier in the transplant course and had higher rates of lymphopenia, neutropenia, corticosteroid use, and ribavirin therapy. Multivariate analysis identified lymphopenia and corticosteroid use (>30 mg/d) as independent risk factors for LRTD occurrence. The overall mortality at day 30 after hMPV detection was 2% for URTD, 12% for possible LRTD, and 21% for proven LRTD. Lymphopenia was the only independent risk factor associated with day 30 mortality in LRTD cases.

CONCLUSIONS

These findings highlight the significance of lymphopenia and corticosteroid use in the development and severity of hMPV infections after allo-HCT, with lymphopenia being a predictor of higher mortality in LRTD cases.

Risk factors for severity in seasonal respiratory viral infections and how they guide management in hematopoietic cell transplant recipients

PURPOSE OF REVIEW

Seasonal respiratory virus infections (RVIs) often progress to severe diseases in hematopoietic cell transplant (HCT) recipients. This review summarizes the current evidence on risk factors for the severity of RVIs in this high-risk population and provides clinical management.

RECENT FINDINGS

The likelihood of the respiratory viral disease progression depends on the immune status of the host and the type of virus. Conventional host factors, such as the immunodeficiency scoring index and the severe immunodeficiency criteria, have been utilized to estimate the risk of progression to severe disease, including mortality. Recent reports have suggested nonconventional risk factors, such as hyperglycemia, hypoalbuminemia, prior use of antibiotics with broad anaerobic activity, posttransplant cyclophosphamide, and pulmonary impairment after RVIs. Identifying novel and modifiable risk factors is important with the advances of novel therapeutic and preventive interventions for RVIs.

SUMMARY

Validation of recently identified risk factors for severe RVIs in HCT recipients is required. The development of innovative interventions along with appropriate risk stratification is critical to improve outcomes in this vulnerable population.

Respiratory virus infections after allogeneic stem cell transplantation: Current understanding, knowledge gaps, and recent advances

Before the COVID-19 pandemic, common community-acquired seasonal respiratory viruses (CARVs) were a significant threat to the health and well-being of allogeneic hematopoietic cell transplant (allo-HCT) recipients, often resulting in severe illness and even death. The pandemic has further highlighted the significant risk that immunosuppressed patients, including allo-HCT recipients, face when infected with SARS-CoV-2. As preventive transmission measures are relaxed and CARVs circulate again among the community, including in allo-HSCT recipients, it is crucial to understand the current state of knowledge, gaps, and recent advances regarding CARV infection in allo-HCT recipients. Urgent research is needed to identify seasonal respiratory viruses as potential drivers for future pandemics.

Immunocompromised Host Pneumonia: Definitions and Diagnostic Criteria: An Official American Thoracic Society Workshop Report

Pneumonia imposes a significant clinical burden on people with immunocompromising conditions. Millions of individuals live with compromised immunity because of cytotoxic cancer treatments, biological therapies, organ transplants, inherited and acquired immunodeficiencies, and other immune disorders. Despite broad awareness among clinicians that these patients are at increased risk for developing infectious pneumonia, immunocompromised people are often excluded from pneumonia clinical guidelines and treatment trials. The absence of a widely accepted definition for immunocompromised host pneumonia is a significant knowledge gap that hampers consistent clinical care and research for infectious pneumonia in these vulnerable populations. To address this gap, the American Thoracic Society convened a workshop whose participants had expertise in pulmonary disease, infectious diseases, immunology, genetics, and laboratory medicine, with the goal of defining the entity of immunocompromised host pneumonia and its diagnostic criteria.

Exposure to antibiotics with anaerobic activity before respiratory viral infection is associated with respiratory disease progression after hematopoietic cell transplant

We examined associations between specific antibiotic exposures and progression to lower respiratory tract disease (LRTD) following individual respiratory viral infections (RVIs) after hematopoietic cell transplantation (HCT). We analyzed allogeneic HCT recipients of all ages with their first RVI during the first 100 days post-HCT. For the 21 days before RVI onset, we recorded any receipt of specific groups of antibiotics, and the cumulative sum of the number of antibiotics received for each day (antibiotic-days). We used Cox proportional hazards models to assess the relationship between antibiotic exposure and progression to LRTD. Among 469 patients with RVI, 124 progressed to LRTD. Compared to no antibiotics, use of antibiotics with broad anaerobic activity in the prior 21 days was associated with progression to LRTD after adjusting for age, virus type, hypoalbuminemia, neutropenia, steroid use, and monocytopenia (HR 2.2, 95% CI 1.1-4.1). Greater use of those antibiotics (≥7 antibiotic days) was also associated with LRTD in adjusted models (HR 2.2, 95% CI 1.1-4.3). Results were similar after adjusting for lymphopenia instead of monocytopenia. Antibiotic use is associated with LRTD after RVI across different viruses in HCT recipients. Prospective studies using anaerobe-sparing antibiotics should be explored to assess impact on LRTD in patients undergoing HCT.

Respiratory viruses in hematopoietic cell transplant candidates: impact of preexisting lower tract disease on outcomes

In myeloablative allogeneic HCT recipients, pretransplant LRD by any virus was associated with increased mortality.

Pretransplant respiratory virus infections (RVIs) have been shown to negatively affect hematopoietic cell transplantation (HCT) outcomes. The impact of and need for delay of HCT for pretransplant infection with human rhinovirus (HRV) or endemic human coronavirus (HCoV; 229E, OC43, NL63, and HKU1) remain controversial. We analyzed the impact of symptomatic RVI within ≤90 days before HCT on overall mortality, posttransplant lower respiratory tract disease (LRD), and days alive and out of hospital (DAOH) by day 100 post-HCT in multivariable models. Among 1,643 adult HCT recipients (58% allogeneic recipients), 704 (43%) were tested for RVI before HCT, and 307 (44%) tested positive. HRV was most commonly detected (56%). Forty-five (15%) of 307 HCT recipients had LRD with the same virus early after HCT. Pretransplant upper respiratory tract infection (URI) with influenza, respiratory syncytial virus, adenovirus, human metapneumovirus, parainfluenza virus, HRV, or endemic HCoV was not associated with increased overall mortality or fewer DAOH. However, in allogeneic recipients who received myeloablative conditioning, LRD due to any respiratory virus, including HRV alone, was associated with increased overall mortality (adjusted hazard ratio, 10.8 [95% confidence interval, 3.29-35.1] for HRV and 3.21 [95% confidence interval, 1.15-9.01] for all other viruses). HRV LRD was also associated with fewer DAOH. Thus, the presence of LRD due to common respiratory viruses, including HRV, before myeloablative allogeneic HCT was associated with increased mortality and hospitalization. Pretransplant URI due to HRV and endemic HCoV was not associated with these outcomes. Improved management strategies for pretransplant LRD are warranted.

Novel factors to predict respiratory viral disease progression in allogeneic hematopoietic cell transplant recipients

We assessed novel factors and the immunodeficiency scoring index (ISI) to predict progression to lower respiratory tract infection (LRTI) among hematopoietic cell transplant (HCT) recipients presenting with upper respiratory tract infection (URTI) with 12 viruses in the PCR era. We retrospectively analyzed the first respiratory virus detected by multiplex PCR in allogeneic HCT recipients (4/2008-9/2018). We used Cox proportional hazards models to examine factors for progression to LRTI within 90 days among patients presenting with URTI. A total of 1027 patients (216 children and 811 adults) presented with URTI only. Among these, 189 (18%) progressed to LRTI (median: 12 days). Multivariable models demonstrated a history of  >1 transplant, age  ≥40 years, time post-HCT (≤30 days), systemic steroids, hypoalbuminemia, hyperglycemia, cytopenia, and high ISI (scores 7-12) were associated with an increased risk of progression to LRTI. Respiratory syncytial virus and human metapneumovirus showed the highest progression risk. Patients with ≥3 independent risk factors or high ISI scores were highly likely to progress to LRTI. We identified novel risk factors for progression to LRTI, including history of multiple transplants and hyperglycemia, suggesting an intervention opportunity with glycemic control. ISI and number of risk factors appear to predict disease progression across several viruses.

Frequent lower respiratory tract disease in hematological patients with parainfluenza virus type 3 infection

Human parainfluenza virus type 3 (HPIV-3) may cause lower respiratory tract infection disease (LRTI-D) after hematopoietic stem cell transplantation (HSCT). Most previous have studies focused on recipients of HSCT whereas data on characteristics and outcomes in patients with hematological malignancies (HMs) compared to non-hematological patients are limited. The prognostic value of viral load in respiratory specimens remains elusive. In a 2-year retrospective study, we determined the frequencies of LRTI-D in HM, HSCT, and in non-hematological patients, and HPIV-3 levels in respiratory tract secretions. Among 98 patients with HPIV-3 infection, including 31 HSCT and 40 HM, 36 had a diagnosis of LRTI-D. LRTI-D was significantly more frequent in patients with HM or HSCT (n = 32, 45.1%) than in non-hematological patients (n = 4, 14.8%) (p = 0.006). The median HPIV-3 loads were high in upper respiratory tract secretions regardless of the presence or absence of LRTI-D (8.3 log₁₀ vs. 7.6 log₁₀ TCID₅₀ /10⁶ cells). HPIV-3 loads in respiratory tract samples in HM were not significantly higher than those found in HSCT but significantly higher than in non-hematological patients (p = 0.007). In conclusion, LRTI-D was frequent in HM patients who were diagnosed with HPIV-3 infection.

Human Metapneumovirus Pneumonia Precipitating Acute Respiratory Distress Syndrome in an Adult Patient

Acute respiratory distress syndrome (ARDS) is often due to direct lung injury, trauma, surgery, or infection. Making a definitive diagnosis may be difficult initially, as clinical manifestations are nonspecific until the disease progresses. We present a case of human metapneumovirus (hMPV) pulmonary infection precipitating ARDS. A 51-year-old woman presented with one week of pleuritic chest pain, dyspnea, wheezing, subjective fever, and productive cough prior to presentation. Her medical history was significant for human immunodeficiency virus (HIV) with an unknown CD4 count and viral load, pulmonary sarcoidosis, asthma, and being an active smoker. On admission, the patient was dyspneic and using accessory muscles to breathe. She was afebrile and hypotensive. Physical examination revealed bilateral diffuse crackles. Her white blood cell (WBC) count was 7.7 K/mcL. A chest radiograph demonstrated bilateral lung opacifications suggestive of pneumonia, possibly Pneumocystis jiroveci pneumonia (PJP). Broad-spectrum antibiotics, including PJP treatment, corticosteroids, and fluids, were started. The patient received approximately 4 liters of intravenous fluids; yet, she remained hypotensive and required norepinephrine. Chest computed tomography (CT) demonstrated bilateral consolidations. Arterial blood gas (ABG) showed a partial pressure of oxygen (PaO2) of 55 mmHg. The patient was intubated for acute hypoxemic respiratory failure and had a PaO2/fraction of inspired oxygen (FiO2) < 100. Repeat ABG within 12 hours showed a potential of hydrogen (pH) of 7.34, partial pressure of carbon dioxide (pCO2) of 42 mmHg, and a PaO2 of 130 mmHg. Bronchoalveolar lavage revealed only hMPV. The patient was managed supportively and extubated three days later. She was discharged home without oxygen requirement. hMPV causes respiratory infections, most commonly in the extremes of age and immunocompromised patients. The treatment is supportive. Our patient developed acute hypoxemic respiratory failure secondary to an hMPV infection. hMPV pneumonia should be considered as a differential diagnosis in patients with severe respiratory illness and ARDS in order to promote antibiotic stewardship.

Risk factors for seasonal human coronavirus lower respiratory tract infection after hematopoietic cell transplantation

We demonstrate risk factors for HCoV LRTI in allogeneic HCT recipients and significance of virologic documentation by BAL on mortality.

Hyperglycemia associated with steroid use appears to be a strong predictor of HCoV disease progression.

Data are limited regarding risk factors for lower respiratory tract infection (LRTI) caused by seasonal human coronaviruses (HCoVs) and the significance of virologic documentation by bronchoalveolar lavage (BAL) on outcomes in hematopoietic cell transplant (HCT) recipients. We retrospectively analyzed patients undergoing allogeneic HCT (4/2008-9/2018) with HCoV (OC43/NL63/HKU1/229E) detected by polymerase chain reaction during conditioning or post-HCT. Risk factors for all manifestations of LRTI and progression to LRTI among those presenting with HCoV upper respiratory tract infection (URTI) were analyzed by logistic regression and Cox proportional hazard models, respectively. Mortality rates following HCoV LRTI were compared according to virologic documentation by BAL. A total of 297 patients (61 children and 236 adults) developed HCoV infection as follows: 254 had URTI alone, 18 presented with LRTI, and 25 progressed from URTI to LRTI (median, 16 days; range, 2-62 days). Multivariable logistic regression analyses showed that male sex, higher immunodeficiency scoring index, albumin <3 g/dL, glucose >150 mg/dL, and presence of respiratory copathogens were associated with occurrence of LRTI. Hyperglycemia with steroid use was associated with progression to LRTI (P < .01) in Cox models. LRTI with HCoV detected in BAL was associated with higher mortality than LRTI without documented detection in BAL (P < .01). In conclusion, we identified factors associated with HCoV LRTI, some of which are less commonly appreciated to be risk factors for LRTI with other respiratory viruses in HCT recipients. The association of hyperglycemia with LRTI might provide an intervention opportunity to reduce the risk of LRTI.

Paramyxovirus infections in hematopoietic cell transplant recipients

PURPOSE OF REVIEW

In hematopoietic cell transplant (HCT) recipients, paramyxovirus infections are major viral respiratory tract infections that, if they progress to lower respiratory tract infections, are associated with reduced survival rates in this population. There are important knowledge gaps regarding treatment decisions for HCT recipients with these infections and in the identification of risk factors that predict infection severity. Here, we review recent data on paramyxovirus infections in HCT recipients focusing on risk factors, new diagnostic and prognostic tools, and management including new drugs and vaccines under development.

RECENT FINDINGS

Multiplexed molecular assays associated with immunodeficiency scoring index for respiratory syncytial virus (RSV) have improved our understanding of the epidemiology of RSV and other paramyxovirus infections and the risk factors for worse outcomes. Novel antiviral drugs, monoclonal antibodies, and vaccines are under evaluation with mixed preliminary results.

SUMMARY

Advances in our knowledge of paramyxovirus infections in HCT recipients in the last two decades contributed to better strategies for management and prevention of these infections. A widespread understanding of how to stratify HCT recipients with paramyxovirus infections who would benefit most from antiviral therapy remains to be ascertained. Vaccines and new drugs under development may mitigate the burden of paramyxovirus infections.

Community-Acquired Respiratory Viruses in Transplant Patients: Diversity, Impact, Unmet Clinical Needs

Patients undergoing solid-organ transplantation (SOT) or allogeneic hematopoietic cell transplantation (HCT) are at increased risk for infectious complications. Community-acquired respiratory viruses (CARVs) pose a particular challenge due to the frequent exposure pre-, peri-, and posttransplantation. Although influenza A and B viruses have a top priority regarding prevention and treatment, recent molecular diagnostic tests detecting an array of other CARVs in real time have dramatically expanded our knowledge about the epidemiology, diversity, and impact of CARV infections in the general population and in allogeneic HCT and SOT patients. These data have demonstrated that non-influenza CARVs independently contribute to morbidity and mortality of transplant patients. However, effective vaccination and antiviral treatment is only emerging for non-influenza CARVs, placing emphasis on infection control and supportive measures. Here, we review the current knowledge about CARVs in SOT and allogeneic HCT patients to better define the magnitude of this unmet clinical need and to discuss some of the lessons learned from human influenza virus, respiratory syncytial virus, parainfluenzavirus, rhinovirus, coronavirus, adenovirus, and bocavirus regarding diagnosis, prevention, and treatment.

Clinical and Radiologic Characteristics of Human Metapneumovirus Infections in Adults, South Korea

Clinical features of human metapneumovirus (HMPV) infection have not been well documented for adults. We investigated clinical and radiologic features of HMPV infection in 849 adults in a tertiary hospital in South Korea. We classified patients into groups on the basis of underlying diseases: immunocompetent patients, solid tumor patients, solid organ transplantation recipients, hematopoietic stem cell transplant recipients, hematologic malignancy patients, and patients receiving long-term steroid treatment. Of 849 HMPV-infected patients, 756 had community-acquired infections, 579 had pneumonia, and 203 had infections with other pathogens. Mortality rates were highest in hematopoietic stem cell transplantation recipients (22% at 30 days). Older age, current smoking, and underlying disease were associated with HMPV pneumonia. Body mass index and an immunocompromised state were associated with 30-day mortality rates in HMPV-infected patients. Bronchial wall thickening, ground-glass opacity, and ill-defined centrilobular nodules were common computed tomography findings for HMPV pneumonia. Macronodules and consolidation were observed in <50% of patients.

Respiratory Virus Infections of the Stem Cell Transplant Recipient and the Hematologic Malignancy Patient

Respiratory virus infections in hematologic stem cell transplant recipients and patients with hematologic malignancies are increasingly recognized as a cause of significant morbidity and mortality. The often overlapping clinical presentation makes molecular diagnostic strategies imperative for rapid diagnosis and to inform understanding of the changing epidemiology of each of the respiratory viruses. Most respiratory virus infections are managed with supportive therapy, although there is effective antiviral therapy for influenza. The primary focus should remain on primary prevention infection control procedures and isolation precautions, avoidance of ill contacts, and vaccination for influenza.

Respiratory Virus Infections in Hematopoietic Cell Transplant Recipients

Highly immunocompromised pediatric and adult hematopoietic cell transplant (HCT) recipients frequently experience respiratory infections caused by viruses that are less virulent in immunocompetent individuals. Most of these infections, with the exception of rhinovirus as well as adenovirus and parainfluenza virus in tropical areas, are seasonal variable and occur before and after HCT. Infectious disease management includes sampling of respiratory specimens from nasopharyngeal washes or swabs as well as sputum and tracheal or tracheobronchial lavages. These are subjected to improved diagnostic tools including multiplex PCR assays that are routinely used allowing for expedient detection of all respiratory viruses. Disease progression along with high mortality is frequently associated with respiratory syncytial virus, parainfluenza virus, influenza virus, and metapneumovirus infections. In this review, we discuss clinical findings and the appropriate use of diagnostic measures. Additionally, we also discuss treatment options and suggest new drug formulations that might prove useful in treating respiratory viral infections. Finally, we shed light on the role of the state of immune reconstitution and on the use of immunosuppressive drugs on the outcome of infection.

Risk Factors for Parainfluenza Virus Lower Respiratory Tract Disease after Hematopoietic Cell Transplantation

Parainfluenza virus (PIV) infection can progress from upper respiratory tract infection (URTI) to lower respiratory tract disease (LRTD) in immunocompromised hosts. Risk factors for progression to LRTD and presentation with LRTD without prior URTI are poorly defined. Hematopoietic cell transplant (HCT) recipients with PIV infection were retrospectively analyzed using standardized definitions of LRTD. PIV was detected in 540 HCT recipients; 343 had URTI alone and 197 (36%) had LRTD (possible, 76; probable, 19; proven, 102). Among 476 patients with positive nasopharyngeal samples, the cumulative incidence of progression to probable/proven LRTD by day 40 was 12%, with a median time to progression of 7 days (range, 2 to 40). In multivariable analysis monocytopenia (hazard ratio, 2.22; P = .011), steroid use ≥1mg/kg prior to diagnosis (hazard ratio, 1.89; P = .018), co-pathogen detection in blood (hazard ratio, 3.21; P = .027), and PIV type 3 (hazard ratio, 3.57; P = .032) were associated with increased progression risk. In the absence of all 4 risk factors no patients progressed to LRTD, whereas progression risk increased to >30% if 3 or more risk factors were present. Viral load or ribavirin use appeared to have no effect on progression. Among 121 patients with probable/proven LRTD, 64 (53%) presented LRTD without prior URTI, and decreased lung function before infection and lower respiratory co-pathogens were risk factors for this presentation. Mortality was unaffected by the absence of prior URTI. We conclude that the risk of progression to probable/proven LRTD exceeded 30% with ≥3 risk factors. To detect all cases of LRTD, virologic testing of lower respiratory samples is required regardless of URTI symptoms.

Respiratory Viral Infections in Transplant Recipients

Respiratory viral infections (RVIs) are common among the general population; however, these often mild viral illnesses can lead to serious morbidity and mortality among recipients of hematopoietic stem cell and solid organ transplantation. The disease spectrum ranges from asymptomatic or mild infections to life-threatening lower respiratory tract infection or long-term airflow obstruction syndromes. Progression to lower respiratory tract infection or to respiratory failure is determined by the intrinsic virulence of the specific viral pathogen as well as various host factors, including the type of transplantation, status of the host’s immune dysfunction, the underlying disease, and other comorbidities. This chapter focuses on the epidemiology, clinical manifestations, diagnosis, and management of RVIs in this susceptible population and includes respiratory syncytial virus, parainfluenza virus, human metapneumovirus, influenza virus, human coronavirus, and human rhinovirus. The optimal management of these infections is limited by the overall paucity of available treatment, highlighting the need for new antiviral drug or immunotherapies.

Managing pulmonary complications in allogeneic hematopoietic stem cell transplantation

Introduction: Progress in allogeneic hematopoietic stem cell transplantation (HSCT) procedures has been associated with improved survival in HSCT recipients. However, they have also brought to light organ-specific complications, especially pulmonary complications. In this setting, pulmonary complications are consistently associated with poor outcomes, and improved management of these complications is required. Areas covered: We review the multiple infectious and noninfectious lung complications that occur both early and late after allogeneic HSCT. This includes the description of these complications, risk factors, diagnostic approach and outcome. A literature search was performed using PubMed-indexed journals. Expert commentary: Multiple lung complications after allogeneic HSCT can be diagnosed concomitantly and require a multidisciplinary approach. A specific clinical evaluation including a precise analysis of a lung CT scan is necessary. Management of these lung complications, especially the noninfectious ones, is impaired by the lack of prospective, randomized control trials, suggesting preventive strategies should be developed.

Respiratory Viral Infections in Patients With Cancer or Undergoing Hematopoietic Cell Transplant

Survival rates for pediatric cancer have steadily improved over time but it remains a significant cause of morbidity and mortality among children. Infections are a major complication of cancer and its treatment. Community acquired respiratory viral infections (CRV) in these patients increase morbidity, mortality and can lead to delay in chemotherapy. These are the result of infections with a heterogeneous group of viruses including RNA viruses, such as respiratory syncytial virus (RSV), influenza virus (IV), parainfluenza virus (PIV), metapneumovirus (HMPV), rhinovirus (RhV), and coronavirus (CoV). These infections maintain a similar seasonal pattern to those of immunocompetent patients. Clinical manifestations vary significantly depending on the type of virus and the type and degree of immunosuppression, ranging from asymptomatic or mild disease to rapidly progressive fatal pneumonia Infections in this population are characterized by a high rate of progression from upper to lower respiratory tract infection and prolonged viral shedding. Use of corticosteroids and immunosuppressive therapy are risk factors for severe disease. The clinical course is often difficult to predict, and clinical signs are unreliable. Accurate prognostic viral and immune markers, which have become part of the standard of care for systemic viral infections, are currently lacking; and management of CRV infections remains controversial. Defining effective prophylactic and therapeutic strategies is challenging, especially considering, the spectrum of immunocompromised patients, the variety of respiratory viruses, and the presence of other opportunistic infections and medical problems. Prevention remains one of the most important strategies against these viruses. Early diagnosis, supportive care and antivirals at an early stage, when available and indicated, have proven beneficial. However, with the exception of neuraminidase inhibitors for influenza infection, there are no accepted treatments. In high-risk patients, pre-emptive treatment with antivirals for upper respiratory tract infection (URTI) to decrease progression to LRTI is a common strategy. In the future, viral load and immune markers may prove beneficial in predicting severe disease, supporting decision making and monitor treatment in this population.

Human Metapneumovirus Infection: Pneumonia Risk Factors in Patients With Solid Organ Transplantation and Computed Tomography Findings

BACKGROUND

Human metapneumovirus (HMPV) is a newly detected pathogen that can cause lower respiratory tract disease. Clinical characteristics, computed tomography (CT) findings, and outcomes of HMPV pneumonia in patients with solid organ transplantation (SOT) have not been well demonstrated.

METHODS

Between January 2010 and February 2016, clinical and imaging findings of 59 patients with SOT (types of organ: kidney, 37; liver, 16; heart, 4; and pancreas and kidney, 2) who had HMPV infection detected in nasopharyngeal or bronchoalveolar lavage by reverse transcription polymerase chain reaction were retrospectively evaluated.

RESULTS

Most (90%) of the patients were detected between March and June. In the 59 patients with SOT with upper respiratory tract infection (URI), 29 (49%) progressed to lower respiratory tract disease after a median of 7 days (range, 2-31 days). Coinfection was noted in 39% of the patients. In Cox proportional hazards analysis, low lymphocyte count (≤0.7 × 10/μL; hazard ratio, 2.24; 95% confidence interval, 1.04-4.85; P = 0.04) and high C-reactive protein (>10 mg/dL; hazard ratio, 2.93; 95% confidence interval, 1.19-7.21; P = 0.02) at URI diagnosis were associated with HMPV pneumonia. On CT, HMPV pneumonia presented as bilateral ill-defined centrilobular nodules, consolidation and ground-glass opacities, whereas lymphadenopathy or effusion is not common. There were no significantly different imaging CT findings between patients with HMPV infection alone and those with coinfection.

CONCLUSIONS

Human metapneumovirus pneumonias were detected in nearly half of patients with SOT showing URI symptoms with positive HMPV, and low lymphocyte count and high C-reactive protein at URI diagnosis were significant factors associated with HMPV pneumonia.

Human Rhinovirus Infections in Hematopoietic Cell Transplant Recipients: Risk Score for Progression to Lower Respiratory Tract Infection

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Risk factors for rhinovirus lower respiratory tract infection are not well characterized.

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Several risk factors in hematopoietic cell transplant recipients were identified.

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A risk score for progression to lower respiratory tract infection was developed.

Human rhinovirus lower respiratory tract infection (LRTI) is associated with mortality after hematopoietic cell transplantation (HCT); however, risk factors for LRTI are not well characterized. We sought to develop a risk score for progression to LRTI from upper respiratory tract infection (URTI) in HCT recipients. Risk factors for LRTI within 90 days were analyzed using Cox regression among HCT recipients with rhinovirus URTI between January 2009 and March 2016. The final multivariable model included factors with a meaningful effect on the bootstrapped optimism corrected concordance statistic. Weighted score contributions based on hazard ratios were determined. Cumulative incidence curves estimated the probability of LRTI at various score cut-offs. Of 588 rhinovirus URTI events, 100 (17%) progressed to LRTI. In a final multivariable model allogeneic grafts, prior rhinovirus URTI, low lymphocyte count, low albumin, positive cytomegalovirus serostatus, recipient statin use, and steroid use ≥2 mg/kg/day were associated with progression to LRTI. A weighted risk score cut-off with the highest sensitivity and specificity was determined. Risk scores above this cut-off were associated with progression to LRTI (cumulative incidence 28% versus 11% below cut-off; P < .001). The weighted risk score for progression to rhinovirus LRTI can help identify and stratify patients for clinical management and for future clinical trials of therapeutics in HCT recipients.

A Multicenter Consortium to Define the Epidemiology and Outcomes of Inpatient Respiratory Viral Infections in Pediatric Hematopoietic Stem Cell Transplant Recipients

BACKGROUND

Respiratory virus infections (RVIs) pose a threat to children undergoing hematopoietic stem cell transplantation (HSCT). In this era of sensitive molecular diagnostics, the incidence and outcome of HSCT recipients who are hospitalized with RVI (H-RVI) are not well described.

METHODS

A retrospective observational cohort of pediatric HSCT recipients (between January 2010 and June 2013) was assembled from 9 US pediatric transplant centers. Their medical charts were reviewed for H-RVI events within 1 year after their transplant. An H-RVI diagnosis required respiratory signs or symptoms plus viral detection (human rhinovirus/enterovirus, human metapneumovirus, influenza, parainfluenza, coronaviruses, and/or respiratory syncytial virus). The incidence of H-RVI was calculated, and the association of baseline HSCT factors with subsequent pulmonary complications and death was assessed.

RESULTS

Among 1560 HSCT recipients, 259 (16.6%) acquired at least 1 H-RVI within 1 year after their transplant. The median age of the patients with an H-RVI was lower than that of patients without an H-RVI (4.8 vs 7.1 years; P < .001). Among the patients with a first H-RVI, 48% required some respiratory support, and 14% suffered significant pulmonary sequelae. The all-cause and attributable case-fatality rates within 3 months of H-RVI onset were 11% and 5.4%, respectively. Multivariate logistic regression revealed that H-RVI onset within 60 days of HSCT, steroid use in the 7 days before H-RVI onset, and the need for respiratory support at H-RVI onset were associated with subsequent morbidity or death.

CONCLUSION

Results of this multicenter cohort study suggest that H-RVIs are relatively common in pediatric HSCT recipients and contribute to significant morbidity and death. These data should help inform interventional studies specific to each viral pathogen.

Antibiotic Exposure Prior to Respiratory Viral Infection Is Associated with Progression to Lower Respiratory Tract Disease in Allogeneic Hematopoietic Cell Transplant Recipients

Recent publications note an association between antibiotic exposure and respiratory viral infections (RVIs). Antibiotics affect microbiota and impair immune response against RVIs in mice, and low microbiome diversity is associated with pulmonary complications including viral lower respiratory tract disease (LRTD) in hematopoietic cell transplantation (HCT) recipients. In this study, we examined whether antibiotic exposure was associated with increased risk of disease progression in RVIs post-transplantation. We analyzed patients who underwent allogeneic HCT (June 2008 to February 2016) and had their first RVI due to parainfluenza virus (PIV), respiratory syncytial virus (RSV), or human metapneumovirus (MPV) during the initial 100 days post-transplantation. Antibiotic exposure in the 3 weeks before RVI onset was defined as (1) use of specific antibiotics versus none of these antibiotics and (2) number of antibiotic-days. Cox proportional hazards models were used to examine associations between antibiotic exposures and risk of viral disease progression to proven/probable/possible LRTD. Ninety HCT recipients (84 adults, 6 children) fulfilled study criteria; 33 progressed to LRTD. The number of antibiotic-days was associated with progression to LRTD after adjusting for neutropenia, steroid use, and either lymphopenia (hazard ratio, 1.41 [95% confidence interval, 1.04 to 1.92], P = .027) or monocytopenia (hazard ratio, 1.46 [95% confidence interval, 1.11 to 1.91], P = .006). Specific antibiotic classes was not associated with the outcome. Cumulative antibiotic exposure immediately before RVI onset is a risk factor for disease progression following PIV, RSV, and MPV infections post-transplantation. Larger cohort studies are needed to determine the impact of specific antibiotics or antibiotic classes on disease severity.

Radiographic and CT Features of Viral Pneumonia

Viruses are the most common causes of respiratory infection. The imaging findings of viral pneumonia are diverse and overlap with those of other nonviral infectious and inflammatory conditions. However, identification of the underlying viral pathogens may not always be easy. There are a number of indicators for identifying viral pathogens on the basis of imaging patterns, which are associated with the pathogenesis of viral infections. Viruses in the same viral family share a similar pathogenesis of pneumonia, and the imaging patterns have distinguishable characteristics. Although not all cases manifest with typical patterns, most typical imaging patterns of viral pneumonia can be classified according to viral families. Although a definite diagnosis cannot be achieved on the basis of imaging features alone, recognition of viral pneumonia patterns may aid in differentiating viral pathogens, thus reducing the use of antibiotics. Recently, new viruses associated with recent outbreaks including human metapneumovirus, severe acute respiratory syndrome coronavirus, and Middle East respiratory syndrome coronavirus have been discovered. The imaging findings of these emerging pathogens have been described in a few recent studies. This review focuses on the radiographic and computed tomographic patterns of viral pneumonia caused by different pathogens, including new pathogens. Clinical characteristics that could affect imaging, such as patient age and immune status, seasonal variation and community outbreaks, and pathogenesis, are also discussed. The first goal of this review is to indicate that there are imaging features that should raise the possibility of viral infections. Second, to help radiologists differentiate viral infections, viruses in the same viridae that have similar pathogenesis and can have similar imaging characteristics are shown. By considering both the clinical and radiologic characteristics, radiologists can suggest the diagnosis of viral pneumonia. ^©RSNA, 2018.

Initial High Viral Load Is Associated with Prolonged Shedding of Human Rhinovirus in Allogeneic Hematopoietic Cell Transplant Recipients

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We examined prolonged shedding of rhinovirus after stem cell transplantation.

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The median shedding duration of rhinovirus was similar between species.

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Initial high viral load was a risk factor for prolonged shedding of rhinovirus.

Recent data suggest human rhinovirus (HRV) is associated with lower respiratory tract infection and mortality in hematopoietic cell transplant (HCT) recipients. Examining risk factors for prolonged viral shedding may provide critical insight for the development of novel therapeutics and help inform infection prevention practices. Our objective was to identify risk factors for prolonged shedding of HRV post-HCT. We prospectively collected weekly nasal samples from allogeneic HCT recipients from day 0 to day 100 post-transplant, and performed real-time reverse transcriptase PCR (December 2005 to February 2010). Subjects with symptomatic HRV infection and a negative test within 2 weeks of the last positive were included. Duration of shedding was defined as time between the first positive and first negative samples. Cycle threshold (Ct) values were used as a proxy for viral load. HRV species were identified by sequencing the 5′ noncoding region. Logistic regression analyses were performed to evaluate factors associated with prolonged shedding (≥21 days). We identified 38 HCT recipients with HRV infection fulfilling study criteria (32 adults, 6 children). Median duration of shedding was 9.5 days (range, 2 to 89 days); 18 patients had prolonged shedding. Among 26 samples sequenced, 69% were species A, and species B and C accounted for 15% each; the median shedding duration of HRV did not differ among species (P = .17). Bivariable logistic regression analyses suggest that initial high viral load (low Ct value) is associated with prolonged shedding. HCT recipients with initial high viral loads are at risk for prolonged HRV viral shedding.

Post-transplant Viral Respiratory Infections in the Older Patient: Epidemiology, Diagnosis, and Management

Organ and stem cell transplantation has been one of the greatest advances in modern medicine, and is the primary treatment modality for many end-stage diseases. As our population ages, so do the transplant recipients, and with that comes many new challenges. Respiratory viruses have been a large contributor to the mortality and morbidity of solid organ transplant (SOT) and hematopoietic stem cell transplant (HSCT) recipients. Respiratory viruses are generally a long-term complication of transplantation and primarily acquired in the community. With the emergence of molecular methods, newer respiratory viruses are being detected. Respiratory viruses appear to cause severe disease in the older transplant population. Influenza vaccine remains the mainstay of prevention in transplant recipients, although immunogenicity of current vaccines is suboptimal. Limited therapies are available for other respiratory viruses. The next decade will likely bring newer antivirals and vaccines to the forefront. Our goal is to provide the most up to date knowledge of respiratory viral infections in our aging transplant population.

Immunologic Profiling of Human Metapneumovirus for the Development of Targeted Immunotherapy

Human metapneumovirus (hMPV) is a respiratory virus detected in ≥9% of allogeneic hematopoietic stem cell transplant (HSCT) recipients, in whom it can cause significant morbidity and mortality. Given the lack of effective antivirals, we investigated the potential for immunotherapeutic intervention, using adoptively transferred T cells. Thus, we characterized the cellular immune response to the virus and identified F, N, M2-1, M, and P as immunodominant target antigens. Reactive T cells were polyclonal (ie, they expressed CD4 and CD8), T-helper type 1 polarized, and polyfunctional (ie, they produced interferon γ, tumor necrosis factor α, granulocyte-macrophage colony-stimulating factor, and granzyme B), and they were able to kill autologous antigen-loaded targets. The detection of hMPV-specific T cells in HSCT recipients who endogenously controlled active infections support the clinical importance of T-cell immunity in mediating protective antiviral effects. Our results demonstrate the feasibility of developing an immunotherapy for immunocompromised patients with uncontrolled infections.

Respiratory viruses in transplant recipients: more than just a cold. Clinical syndromes and infection prevention principles

OBJECTIVES

The aim of this review is to provide updated information on the clinical spectrum, treatment options, and infection prevention strategies for respiratory viral infections (RVIs) in both solid organ (SOT) and hematopoietic stem cell transplant (HSCT) patients.

METHODS

The MEDLINE and PubMed databases were searched for literature regarding the aforementioned aspects of RVIs, with focus on respiratory syncytial virus, adenovirus, influenza virus, parainfluenza virus, human metapneumovirus, and rhinovirus.

RESULTS

Compared to immunocompetent hosts, SOT and HSCT patients are much more likely to experience a prolonged duration of illness, prolonged shedding, and progression of upper respiratory tract disease to pneumonia when infected with respiratory viruses. Adenovirus and respiratory syncytial virus tend to have the highest mortality and risk for disseminated disease, but all the RVIs are associated with higher morbidity and mortality in these patients than in the general population. These viruses are spread via direct contact and aerosolized droplets, and nosocomial spread has been reported.

CONCLUSIONS

RVIs are associated with high morbidity and mortality among SOT and HSCT recipients. Management options are currently limited or lack strong clinical evidence. As community and nosocomial spread has been reported for all reviewed RVIs, strict adherence to infection control measures is key to preventing outbreaks.

A Retrospective Study Investigating Risks of Acute Respiratory Distress Syndrome and Mortality Following Human Metapneumovirus Infection in Hospitalized Adults

Background

Human metapneumovirus (hMPV) is a relatively recently identified respiratory virus that induces respiratory symptoms similar to those of respiratory syncytial virus infection in children. The characteristics of hMPV-infected adults are unclear because few cases have been reported.

Methods

We conducted a retrospective review of hospitalized adult patients with a positive multiplex real-time polymerase chain reaction assay result from 2012 to 2016 at a single tertiary referral hospital in South Korea. We analyzed clinical characteristics of the enrolled patients and divided patients into an acute respiratory distress syndrome (ARDS) group and a non-ARDS group.

Results

In total, 110 adults were reviewed in this study. Their mean age was 61.4 years, and the majority (n = 105, 95.5%) had comorbidities or were immunocompromised. Most of the patients had pneumonia on chest X-ray (n = 88, 93.6%), 22 (20.0%) had ARDS, and 12 (10.9%) expired during hospitalization. The mortality rate for patients with ARDS was higher than that of the other patients (36.4% vs. 5.7%, P = 0.001). The risk factor for hMPV-associated ARDS was heart failure (odds ratio, 5.24; P = 0.044) and laboratory values were increased blood urea nitrogen and increased C-reactive protein. The acquisition site of infection was divided into community vs. nosocomial; 43 patients (39.1%) had a nosocomial infection. The risk factors for nosocomial infection were an immunocompromised state, malignancy and immunosuppressive treatment.

Conclusions

These data suggest that hMPV is one of the important respiratory pathogens important respiratory pathogen that causes pneumonia/ARDS in elderly, immunocompromised individuals and that it may be transmitted via the nosocomial route.

Antiviral therapy for respiratory viral infections in immunocompromised patients

INTRODUCTION

Respiratory viruses (influenza, parainfluenza, respiratory syncytial virus, coronavirus, human metapneumovirus, and rhinovirus) represent the most common causes of respiratory viral infections in immunocompromised patients. Also, these infections may be more severe in immunocompromised patients than in the general population. Early diagnosis and treatment of viral infections continue to be of paramount importance in immunocompromised patients; because once viral replication and invasive infections are evident, prognosis can be grave. Areas covered: The purpose of this review is to provide an overview of the main antiviral agents used for the treatment of respiratory viral infections in immunocompromised patients and review of the new agents in the pipeline. Expert commentary: Over the past decade, important diagnostic advances, specifically, the use of rapid molecular testing has helped close the gap between clinical scenarios and pathogen identification and enhanced early diagnosis of viral infections and understanding of the role of prolonged shedding and viral loads. Advancements in novel antiviral therapeutics with high resistance thresholds and effective immunization for preventable infections in immunocompromised patients are needed.

Human metapneumovirus infections in hematopoietic cell transplant recipients and hematologic malignancy patients: A systematic review

Over the past decade, reported incidence of human metapneumovirus (hMPV) has increased owing to the use of molecular assays for diagnosis of respiratory viral infections in cancer patients. The seasonality of these infections, differences in sampling strategies across institutions, and small sample size of published studies make it difficult to appreciate the true incidence and impact of hMPV infections. In this systematic review, we summarized the published data on hMPV infections in hematopoietic cell transplant recipients and patients with hematologic malignancy, focusing on incidence, hMPV-associated lower respiratory tract infection (LRTI), mortality, prevention, and management with ribavirin and/or intravenous immunoglobulins. Although the incidence of hMPV infections and hMPV-associated LRTI in this patient population is similar to respiratory syncytial virus or parainfluenza virus and despite lack of directed antiviral therapy, the mortality rate remains low unless patients develop LRTI. In the absence of vaccine to prevent hMPV, infection control measures are recommended to reduce its burden in cancer patients.