Hospitalisations and outpatient visits for undifferentiated fever attributable to scrub typhus in rural south india: retrospective cohort and nested case-control study

Schmidt, W. 2018. Hospitalisations and outpatient visits for undifferentiated fever attributable to scrub typhus in rural south india: retrospective cohort and nested case-control study. [Online]. London School of Hygiene & Tropical Medicine, London, United Kingdom. Available from: https://doi.org/10.17037/DATA.00001025.

Schmidt, W. Hospitalisations and outpatient visits for undifferentiated fever attributable to scrub typhus in rural south india: retrospective cohort and nested case-control study [Internet]. London School of Hygiene & Tropical Medicine; 2018. Available from: https://doi.org/10.17037/DATA.00001025.

Schmidt, W (2018). Hospitalisations and outpatient visits for undifferentiated fever attributable to scrub typhus in rural south india: retrospective cohort and nested case-control study. [Data Collection]. London School of Hygiene & Tropical Medicine, London, United Kingdom. https://doi.org/10.17037/DATA.00001025.

Description

This dataset contains individual-level information collected as part of a study to estimate the proportion of hospitalisations and outpatient visits for undifferentiated fever that may be attributable to scrub typhus in the South Indian state of Tamil Nadu. We conducted house-to-house screening in 48 villages (42965 people, 11964 households) to identify hospitalised or outpatient cases due to undifferentiated fever during the preceding scrub typhus season. We used scrub typhus IgG to determine past infection. We calculated adjusted odds ratios for the association between IgG positivity and case status. Odds ratios were used to estimate population attributable fractions (PAF) indicating the proportion of hospitalised and outpatient fever cases attributable to scrub typhus. We identified 58 cases of hospitalisation and 236 outpatient treatments. 562 people were enrolled as control group to estimate the background IgG sero-prevalence. IgG prevalence was 20.3% in controls, 26.3% in outpatient cases and 43.1% in hospitalised cases. The PAFs suggested that 29.5% of hospitalisations and 6.1% of outpatient cases may have been due to scrub typhus. In villages with a high IgG prevalence (defined as ≥15% among controls), the corresponding PAFs were 43.4% for hospitalisations and 5.6% for outpatients. The estimated annual incidence of scrub typhus was 0.8/1000 people (0.3/1000 in low, and 1.3/1000 in high prevalence villages). Evidence for recall error suggested that the true incidences may be about twice as high as these figures. Conclusions: The study suggests scrub typhus as an important cause for febrile hospitalisations in the community. The results confirm the adequacy of empirical treatment for scrub typhus in hospitalised cases with undifferentiated fever. Since scrub typhus may be rare among stable outpatients, the use of empirical treatment remains doubtful in these. Data request button removed at request of data creator on 06 May 2021. Release of data is subject to approval by Institutional Review Board at Christian Medical College, Vellore. Please contact data creator via email to discuss dataset.

Methods

Description of data capture

Field staff would identify the approximate boundaries of a village using satellite images, and then attempt to cover the whole village through house-to-house enquiry. Houses without anyone present were left out, and not revisited. We used the following eligibility criteria for enrolment of a case of undifferentiated febrile illness: 1) aged 12 years or older, 2) hospitalised for febrile illness, or visited an outpatient department, local clinic or pharmacy due to febrile illness at any time between June 2017 and March 2018, 3) cause for febrile illness not known, or described (by respondent or in available health records) as scrub typhus, malaria, dengue, typhoid, meningitis or pneumonia, 4) absence of leg infection, 5) no operation was done at the hospital, 6) no other surgical cause for fever identified from patients memory or available health records, 7) absence of urinary tract infection (only used to exclude cases if urine culture positive), 8) duration of fever of at least 2 days or duration of fever not known, 9) the fever occurred while residing in the study village and health care was sought at a health centre in the district. Hospitalisation was defined as staying at least for one night. All other health care uses were treated as outpatient / pharmacy visit. If a hospitalised case was not present at the time of the interview, we made an appointment with the participants for blood sampling and questionnaire administration. Absent cases meeting the enrolment criteria for outpatients were not revisited due to logistical constraints. Case and control households were geo-referenced using hand-held GPS receivers. Enrolment of controls We enrolled controls through systematic sampling during house-to-house screening, by contacting household members of every 20th house during the walk. Controls were eligible if they had not sought health care due to febrile illness between June 2017 and March 2018, and were living in the study area during that time. Because of concerns that field workers would predominantly enrol older people and females who were deemed more likely to be present, we used a stratified enrolment procedure, using four strata: females ≥50 years old, females <50 years old, males ≥50 years old, males <50 years old. Field workers enrolled controls in blocks of four, with each stratum being represented once. The aim of this procedure was to obtain a reasonably age and sex balanced control group without requiring a formal sampling frame. Controls were asked to give a blood sample and were asked whether they had had any high grade fever not leading to health care use between June 2017 and March 2018.

Data capture method

Interview: Face-to-face, Measurements and tests

Data Collection Period

From	To
23 March 2018	30 June 2018

Date (Date submitted to LSHTM repository)

15 September 2018

Geographical area covered (offline during plugin upgrade)

North Latitude	East Longitude	South Latitude	West Longitude
13.326	79.5505	12.3996	78.4986

Language(s) of written materials

English

People & Groups

Data Creators	Schmidt, W
Associated roles	Devamani, C (Co-Investigator), Prakash, JJ (Co-Investigator) and Alexander, N (Co-Investigator)
LSHTM Faculty/Department	Faculty of Infectious and Tropical Diseases > Dept of Disease Control
Participating Institutions	London School of Hygiene & Tropical Medicine, London, United Kingdom, Christian Medical College Vellore, Tamil Nadu 632004, India

Projects

Funders

Project	Funder	Grant Number	Funder URI
Hospitalisations and outpatient visits for undifferentiated fever attributable to scrub typhus in rural south india: retrospective cohort and nested case-control study	Medical Research Council	UNSPECIFIED	UNSPECIFIED