Hospitalisations and outpatient visits for undifferentiated fever attributable to scrub typhus in rural South India: Retrospective cohort and nested case-control study

The Incidence of Orientia Tsutsugamushi Infection in Rural South India

Scrub typhus is a common bacterial infection in Asia caused by Orientia tsutsugamushi. This serological cohort study estimated the incidence of infection in a rural population in South India. Participants were enrolled through systematic sampling in 46 villages at baseline, and revisited the following year. Blood samples were tested for IgG antibodies using ELISA, followed by indirect immunofluorescence assays (IFA) in those positive for ELISA at both rounds. A case was defined as sero-conversion (ELISA), or at least a 4-fold titre increase (IFA), between the two time points. In addition to crude incidence rate estimates, we used piecewise linear rates across calendar months, with rates proportional to the monthly incidence of local hospital cases to address seasonality and unequal follow-up times. Of 402 participants, 61.7% were female. The mean age was 46.7 years, (range 13–88). 21 participants showed evidence for serological infection. The estimated incidence was 4.4 per 100 person-years (95% CI 2.8–6.7). The piecewise linear rates approach resulted in a similar estimate of 4.6 per 100 person years (95% CI 2.9–6.9). Considering previous estimates of symptomatic scrub typhus incidence in the same study population, only about 2–5% of infections may result in clinically relevant disease.

Agreement and error of titration assays

Titration assays can be used to define positivity either in terms of a change over time, i.e. seroconversion, or relative to a fixed threshold. The operating characteristics of these definitions depend on the precision of the assay. We present methods for estimating the distribution of errors, at the level of a single replicate, from the distribution of within-pair agreement. When the maximum replicate-level error is one dilution, a simple probability argument is used, with estimation by method of moments. For the more general case, a discretized Gaussian model is used, with maximumum likelihood estimation. These models fit well to eight published datasets. The discretized Gaussian model also allows the potential performance of alternative dilution factors to be assessed. For influenza hemagglutination-inhibition, the approach is compared to a previous Markov chain Monte Carlo data augmentation model. These methods allow the estimation of the underlying error distribution from observed between-replicate differences under repeatability conditions. The results can be used to guide the choice of the fold change necessary to infer seroconversion. Finer dilution factors, e.g. 1.5 rather than 2, could facilitate a better balance between the sensitivity and specificity of titration assays.

Scrub typhus in two COVID-19 patients: a diagnostic dilemma

The authors describe a case series of co-infection with COVID-19 and scrub typhus in two Indian patients. Clinical features like fever, cough, dyspnea and altered sensorium were common in both patients. Case 1 had lymphopenia, elevated IL-6 and history of hypertension, while case 2 had leukocytosis and an increased liver enzymes. Both patients had hypoalbuminemia and required admission to the intensive care unit; one of them succumbed to acute respiratory distress syndrome further complicated by multiple organ dysfunction syndrome. Seasonal tropical infections in COVID-19 patients in endemic settings may lead to significant morbidity and mortality. Therefore, high clinical suspicion and an early diagnosis for co-infections among COVID-19 patients are essential for better patient management.

Clinical characteristics of and antibody response to spotted fever group rickettsial infections in South India: Case series and serological cohort study

OBJECTIVE

The clinical and serological characteristics of spotted fever group rickettsial (SFGR) infections in South Asia are poorly understood. We studied the clinical presentation and the IgM/IgG response in cases enrolled at two health care centres in South India.

METHOD

We enrolled 77 patients. Fifty-seven of these patients were recruited at a tertiary care centre, the remaining 20 at a community hospital (secondary care level). Diagnostic tests included IgM and IgG enzyme-linked immunosorbent assay and polymerase chain reaction. Over a period of 1 year, 41 cases were followed up for repeated sero-analysis.

RESULTS

Median age was 9 years (range 1-79). A rash was present in 74% of cases (57/77). In cases aged <15 years, rash was present in 94% (44/47) vs. 43% (13/30) in cases aged ≥15 years. An eschar was found in two cases (3%). Severe infection or complications occurred in 10 cases (13%). These included central nervous system infection (6/77, 8%), kidney injury (3/77, 4%), shock (3/77, 4%), lung involvement (2/77, 3%) and peripheral gangrene (2/77, 3%). IgM antibody levels increased faster after fever onset than IgG antibodies, peaking at 50 and 60 days, respectively. After the peak, IgM and IgG levels showed a slow decline over one year with less than 50% of cases showing persistent IgG antibody levels.

CONCLUSION

Spotted fever group rickettsial infections in South India may be under-diagnosed, as many cases may not develop a rash. The proportion of cases developing severe infection seems lower than for scrub typhus in this region. IgG seroprevalence may substantially underestimate the proportion in a population with past SFGR infection.

Spectrum of Multiorgan Dysfunction in Scrub Typhus Infection

OBJECTIVES

We planned this study to determine the clinical spectrum and compare incidence of multiorgan dysfunction in children hospitalized with scrub typhus with other etiologies of tropical fever.

DESIGN

Prospective cohort study.

SETTING

Pediatric emergency and PICU services of a university teaching hospital situated in the sub-Himalayan region.

PATIENT

Children aged 2 months to 14 years with acute undifferentiated fever of more than 5 days.

INTERVENTIONS

Detailed fever workup was performed in all children. We compared scrub typhus IgM positive children (cases) with remaining febrile children who were negative for scrub IgM assay (controls) for mortality and morbidity.

MAIN RESULTS

We enrolled 224 febrile children; 76 children (34%) were positive for scrub typhus IgM ELISA. Scrub typhus group had a significantly higher incidence of multiorgan dysfunction [OR 3.5 (95% CI 2.0-6.3); p < 0.001] as compared to non-scrub typhus group requiring supportive care. The incidence of altered sensorium [OR 8.8 (95% CI 3.1-24.9)], seizures [OR 3.0 (95% CI 1.1-8.3)], acute respiratory distress syndrome [OR 17.1 (95% CI 2.1-140.1)], acute renal failure (5% vs. 0%), meningitis [OR 6.2 (95% CI 1.2-31.6)], thrombocytopenia [OR 2.8 (95% CI 1.5-5.1)], transaminitis [OR 2.7 (95% CI 1.6-4.8)], requirement of oxygen [OR 17.8 (95% CI 4.0-80.3)], positive pressure support [OR 3.7 (95% CI 1.2-10.5)] and shock requiring inotropes [OR 3.0 (95% CI 1.3-6.7)] was significantly higher in scrub typhus group as compared to the non-scrub typhus group (Table 1).

CONCLUSIONS

Pediatric scrub typhus who were hospitalized had severe systemic manifestations when compared to other causes of fever.

Misdiagnosis of scrub typhus as hemorrhagic fever with renal syndrome and potential co-infection of both diseases in patients in Shandong Province, China, 2013-2014

Background

Scrub typhus, caused by Orientia tsutsugamushi, an obligate intracellular gram-negative bacterium, along with hemorrhagic fever with renal syndrome (HFRS), caused by hantaviruses, are natural-focus infectious diseases prevalent in Shandong Province, China. Both diseases have similar clinical manifestations in certain disease stages and similar epidemic seasons, which has caused difficulties for physicians in distinguishing them. The aim of this study was to investigate whether misdiagnosis of scrub typhus as HFRS occurred in patients in Shandong Province.

Methods

Serum samples (N = 112) of clinically suspected HFRS patients from 2013 to 2014 in Shandong Province were analyzed with enzyme-linked immunosorbent assay (ELISA) for antibodies to both hantavirus and Orientia tsutsugamushi.

Results

ELISA showed that 56.3% (63/112) and 8.0% (9/112) of clinically suspected HFRS patients were IgM antibody positive to hantavirus and O. tsutsugamushi, respectively. Among the hantavirus IgM antibody positive patients, 7.9% (5/63) were also IgM antibody positive to O. tsutsugamushi. Among the hantavirus IgM antibody negative sera, 8.2% (4/49) of sera were positive to O. tsutsugamushi.

Conclusions

We concluded that some scrub typhus patients were misdiagnosed as HFRS and co-infection of scrub typhus and HFRS might exist in China. Due to the different treatments for scrub typhus and HFRS, physicians should carefully differentiate between scrub typhus and HFRS and consider administering anti-rickettsia antibiotics if treatment for HFRS alone does not work.

Scrub typhus is caused by O. tsutsugamushi and hemorrhagic fever with renal syndrome (HFRS) is caused by hantavirus. Both diseases have similar manifestations and have their peak epidemic season in the fall, which makes their clinical differentiation difficult to be differentiated from each other clinically. In this study, we found that scrub typhus was indeed misdiagnosed as HFRS and co-infection of O. tsutsugamushi and hantaviruses might exist in China. Owing to different treatments of HFRS and scrub typhus, physicians need pay attention to differentiate them; identify co-infection of HFRS and scrub typhus; and consider administering antibiotics if antiviral treatment alone does not work.

High initial IgG antibody levels against Orientia tsutsugamushi are associated with an increased risk of severe scrub typhus infection

BACKGROUND

Scrub typhus is a dominant cause of febrile illness in many parts of Asia. Immunity is limited by the great strain diversity of Orientia tsutsugamushi. It is unclear whether previous infection protects from severe infection or enhances the risk.

METHODS/PRINCIPAL FINDINGS

We studied IgG antibody levels against O. tsutsugamushi at presentation in 636 scrub typhus patients using enzyme-linked immunosorbent assays (ELISA). The association between ELISA optical density (OD) and risk of severe infection was modelled using Poisson regression. OD was categorised as low (<1.0), intermediate (1.0 to 2.9), and high (≥3.0). OD was also modelled as a continuous variable (cubic spline). Median age of cases was 41 years (range 0-85), with 37% having severe infection. Compared to the low category, the age-adjusted risk of severe infection was 1.5 times higher in the intermediate category (95%CI 1.2, 1.9), and 1.3 times higher in the high category (95%CI 1.0, 1.7). The effect was stronger in cases <40 years, doubling the risk in the intermediate and high categories compared to the low category. The effect was more pronounced in cases tested within 7 days of fever onset when IgG ODs are more likely to reflect pre-infection levels.

CONCLUSIONS/SIGNIFICANCE

Intermediate and high IgG antibody levels at the time of diagnosis are associated with a higher risk of severe scrub typhus infection. The findings may be explained by severe infection eliciting an accelerated IgG response or by previous scrub typhus infection enhancing the severity of subsequent episodes.

Risk Factors for Scrub Typhus, Murine Typhus, and Spotted Fever Seropositivity in Urban Areas, Rural Plains, and Peri-Forest Hill Villages in South India: A Cross-Sectional Study

Scrub typhus and spotted fever group rickettsioses are thought to be common causes of febrile illness in India, whereas they rarely test for murine typhus. This cross-sectional study explored the risk factors associated with scrub typhus, tick-borne spotted fever, and murine typhus seropositivity in three different geographical settings, urban, rural, and hill villages in Tamil Nadu, South India. We enrolled 1,353 participants living in 48 clusters. The study included a questionnaire survey and blood sampling. Blood was tested for Orientia tsutsugamushi (scrub typhus), Rickettsia typhi (murine typhus), and spotted fever group Rickettsia IgG using ELISA. The seroprevalence of scrub typhus, spotted fever, and murine typhus were 20.4%, 10.4%, and 5.4%, respectively. Scrub typhus had the highest prevalence in rural areas (28.1%), and spotted fever was most common in peri-forested areas (14.9%). Murine typhus was more common in rural (8.7%) than urban areas (5.4%) and absent in peri-forested hill areas. Agricultural workers had a higher relative risk for scrub typhus, especially in urban areas. For murine typhus, proximity to a waterbody and owning a dog were found to be major risk factors. The main risk factors for spotted fever were agricultural work and living in proximity to a forest. Urban, rural plains, and hill settings display distinct epidemiological pattern of Orientia and rickettsial infections. Although scrub typhus and spotted fever were associated with known risk factors in this study, the findings suggest a different ecology of murine typhus transmission compared with other studies conducted in Asia.

Antibody response following scrub typhus infection: clinical cohort study

OBJECTIVE

Scrub typhus is a common cause of fever in Asia. The antibody response to infection and its effect on subsequent infection are unclear. We studied the IgM and IgG antibody response after infection, accounting for clinical severity.

METHOD

We studied 197 scrub typhus patients for up to 2 years post-infection. Overall, 501 blood samples were analysed for scrub typhus antibodies using ELISA. IgM and IgG ELISA optical densities (OD) were analysed using quantile regression. OD values of 1.0 (IgM) and 1.5 (IgG) were used to define seropositivity.

RESULTS

IgM OD values fell rapidly from an initial peak after infection. 50% of cases were IgM seronegative after 82 days. About 2 years after fever onset, 50% of cases had fitted IgG OD values of <1.5. Patients with high initial IgG OD values (≥2.5, used as a proxy for probable previous scrub typhus infection) had a more sustained IgG response than those with a low initial IgG OD, and more often presented with complications (18/36 = 50% vs. 28/91 = 30.8%, risk ratio = 1.63, 95% CI 1.04, 2.55, P = 0.035). This association was robust to adjusting for age (risk ratio 1.50, 95% CI 0.96, 2.33, P = 0.072).

CONCLUSION

Cross-sectional IgG seroprevalence data substantially underestimate the proportion in a population ever infected with scrub typhus. A high initial IgG as a potential marker for previous scrub typhus infection may be associated with long-term IgG persistence and a higher risk of complicated scrub typhus.