The incidence of Orientia tsutsugamushi infection in rural South India

Abstract

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 titer 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.

CagA-positive Helicobacter pylori may promote and aggravate scrub typhus

“…Epidemiological surveys have shown that the infection rate of H. pylori infection is related to social economic situation, living conditions, sanitary conditions and living habits, occupation and quality of drinking water ( Xu Wenting and Chengfu, 2022 ). The prevalence of scrub typhus is also found in specific populations (e.g., military personnel or plantation workers) and agricultural staff in townships ( Devamani et al, 2022 ). To avoid any influence of environmental and occupational factors on the study results, we strictly matched the regional distribution, age, and gender of the Tsutsugamushi patients and the healthy medical examination population.…”

“…Infection with Orientia tsutsugamushi in humans can manifest with a wide range of clinical symptoms, varying from mild (asymptomatic) to severe and potentially life-threatening conditions ( Park et al, 2021 ; Devamani et al, 2022 ). The underlying mechanisms for these variations are not fully understood, but it was believed that factors such as the strain of Orientia tsutsugamushi and the immune status of the host may play a role ( Elliott et al, 2019 ).…”