Risk factors for acquisition of scrub typhus in children admitted to a tertiary centre and its surrounding districts in South India: a case control study

Abstract

Background Scrub typhus is a mite borne zoonosis common in the tropics with no good preventive strategy. Children are also affected leading to considerable morbidity and mortality. We conducted a case control study and a vector survey to determine the risk factors for acquisition of scrub typhus. Methods A case control study with a 1:2 case control ratio was conducted over a 2 year period at a tertiary care centre and its surrounding districts in South India. Cases were children < 15 years with confirmed scrub typhus. Controls were age and locality matched community controls without fever. Demographic, environmental and behavioural risk factors were obtained in cases and controls by an interview and an environmental survey. A vector survey was also undertaken in the immediate vicinity of the cases. Results Case Control study: 101 cases and 167 controls were analysed. On multivariate analysis, significant association was observed with environmental factors such as the presence of a water body within 100 m of the house (OR 3.56(1.36,9.75); p 0.011), cooking outside the house (OR 5.61 (1.51,23.01); p 0.011), owning pets (OR 3.33(1.16,9.09); p 0.031), and the presence of bushes within 5 m of the house (OR 2.78 (1.11,7.69); p 0.033). Of the behavioural factors, the child going to school by a vehicle (OR 3.12 (2.29,8.37); p 0.006) was associated with an increased risk. Drying clothes on a clothesline showed a trend towards protection from acquiring scrub typhus (OR 0.31 (0.08, 1.08); p 0.077). Vector survey:26 rodents were trapped in as many houses. Trombiculid mites were isolated in 24 houses with 9(34.6%) being able to transmit scrub typhus. 254 trombiculid mites belonging to four species and two genera were collected. Leptotrombidium deliense, (33.5%). Schoengastiella ligula, (11.0%) of the total mite specimens collected. S. ligula always co-existed with L. deliense. The estimated Chigger index for Leptotrombidium deliense and Schoengastiella ligula was 3.27and 1.08 per animal respectively. Conclusions Our study highlights risk factors for scrub typhus, some of which may be modifiable. A clean peri-domestic environment free of vegetation, drying clothes on a clothesline and cooking indoors may decrease the risk of scrub typhus.

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

“…In further studies, the risk of scrub typhus was associated with being female, age > 60 years, 13 in agricultural laborers, being bare-chested at home, and living in dwellings adjacent to scrub land. 12 A pediatric case–control study suggested scrub typhus is more likely in children who have pets and stay in houses less than 100 m from a waterbody and bushes within 5 m. 25 The strong association of agricultural work with scrub typhus in urban areas in our study suggests that infestation with mites may often take place away from urban areas, for example, in those who own agricultural land and go to rural areas for cultivation.…”

Diagnosis of scrub typhus: recent advancements and challenges

“…A study reveals that as compared to behavioral and demographic factors, environmental factors seem to be the most prominent factor responsible for the occurrence of scrub typhus. Living in the vicinity of the water body, cooking outside the home, domesticating pets, and the presence of scrub vegetation in the vicinity of the house all increase the risk of scrub typhus (Lyu et al 2013 ; Varghese et al 2016 ; Rose et al 2019 ). There are two mechanisms for the transmission of O. tsutsugamushi , i.e., transovarial (transmission of Orientia tsutsugamushi from the female to offspring through eggs) and transstadial (passage from mite larva-nymph-adult) (Phasomkusolsil 2009 ).…”

Ecological and behavioural risk factors of scrub typhus in central Vietnam: a case-control study

“…Water drainage or seepage in drier areas was defined as a crucial micro-ecology favoring the presence of chiggers and increased risk of acquiring scrub typhus [ 7 , 41 , 42 ]. Common chigger habitats are grassy edges, soil dampness, and a well nearby the household [ 41 , 42 , 49 ], but water drainage on the household ground/premises was not considered [ 20 , 50 , 51 ]. A sandy/muddy yard or a muddy house floor take up dampness through water drainage after rainfall, which fosters survival of chiggers.…”

“…Reported common risk factors for scrub typhus are bushes around house/working place [ 45 , 51 , 53 , 61 – 64 ], always observing mice around home [ 45 , 60 ], and working near forest/hilly fields [ 24 , 45 , 53 ]. In this study, we highlighted additional factors for Khanh Hoa, including (i) sitting/laying directly on HH floor; (ii) use of full PPE set (socks, boots, long/extra shirt, long/extra trousers, gloves) in the field, (iii) changing of clothes when at home; (iv) HH with sandy or muddy grounds/a muddy floor, or HH with drainage on ground; and (v) workplace near sandy fields.…”