Epidemiology and Risk Factors of Scrub Typhus in Punjab, India: A Matched Case-Control Study, 2018

Abstract

Background: Scrub typhus is an acute febrile zoonotic infection caused by Orientia tsutsugamushi and transmitted through the bite of infected larval trombiculid mites. The disease has increasingly been reported from several ecological regions of India, including Punjab. However, evidence regarding community-level risk factors for scrub typhus in Punjab remains limited. Objectives: To identify environmental, occupational and behavioural risk factors associated with scrub typhus in selected districts of Punjab and to recommend appropriate preventive and control measures. Methods: A concurrent 1:2 matched case-control study was conducted from June to November 2018 in five districts of Punjab: Hoshiarpur, Rupnagar, Shahid Bhagat Singh Nagar, Sahibzada Ajit Singh Nagar and Fatehgarh Sahib. Cases were residents of the selected districts who tested positive for scrub typhus by immunoglobulin M enzyme-linked immunosorbent assay. For each case, two age- and sex-matched community controls without a history of fever during the preceding month were selected from the same locality. Information on socio-demographic characteristics, agricultural activities, environmental exposures, animal contact, rodent exposure, personal habits and protective practices was collected using a pretested semi-structured questionnaire. Matched odds ratios with 95% confidence intervals were calculated. Results: A total of 126 participants, comprising 42 cases and 84 controls, were enrolled. The median age of cases was 33 years, with a range of 1-77 years, and 23 cases (55%) were male. Thirty-two cases (76%) were from rural areas. Fever was present in all cases, followed by generalized weakness in 34 (81%), headache in 27 (64%), nausea or vomiting in 21 (50%) and breathlessness in 21 (50%). Eschar was identified in six cases (14%). Sixteen cases (38%) required hospitalization for 10 days or longer, nine (21%) required mechanical ventilation and three (7%) underwent dialysis. Significant risk factors included having a farm near the residence (matched odds ratio [mOR]: 6.5; 95% confidence interval [CI]: 1.5-28.8), visiting a farm (mOR: 9.0; 95% CI: 2.7-29.7), working in bajra or chari fields (mOR: 5.67; 95% CI: 1.7-19.3), harvesting crops (mOR: 5.67; 95% CI: 1.7-19.3), walking barefoot (mOR: 2.71; 95% CI: 1.1-6.5), walking barefoot on wet surfaces (mOR: 2.86; 95% CI: 1.2-6.8), feeding cattle (mOR: 5.75; 95% CI: 1.9-16.6), entering bushy areas (mOR: 6.25; 95% CI: 2.2-17.9) and sleeping on the ground inside the house (mOR: 21.0; 95% CI: 1.2-358.4). Having a fully cemented floor and bathing after work were protective. Conclusion: Agricultural exposure, contact with vegetation, barefoot walking on wet surfaces, cattle-related activities and sleeping on the ground were important risk factors for scrub typhus in Punjab. Community education, use of protective footwear and clothing, avoidance of bushy areas, improved household flooring and personal hygiene after agricultural work should form part of scrub typhus prevention strategies.

Keywords: Scrub typhus; Orientia tsutsugamushi; Punjab; case-control study; agricultural exposure; risk factors; chigger mites