Understanding behavioural and environmental risk factors for paederus dermatitis: evidence from a case-control study in Sikkim, India, 2022

Paederus dermatitis is an acute contact dermatitis caused by exposure to Paederus insects. Sporadic cases and outbreaks have been reported globally, and environmental risk factors like climate change-induced insect habitat alteration is one reason for such outbreaks. We confirmed and described the outbreak in Sikkim, India. We conducted a case-control study to identify the factors associated with the outbreak. We analysed behavioural and environmental risk factors using an odds ratio (OR). There were 155 cases reported inside the college campus between 24 June and 10 July, 2022. Of the 82 cases interviewed, 76% were students and 88% were males. The median number of days between exposure and the appearance of the rash was one (range: 0–5) day. We compared the risk factors among cases with 83 controls. People who had behaviours like keeping lights on after 10 pm (AOR: 7.38; 95% CI: 3.01–19.81), not clearing the insects before going to bed (AOR: 8.65; 95% CI: 3.29–25.60), were more likely to become cases. Environmental findings included the presence of heavy rainfall (precipitation at 20 mm) in the block preceding the outbreak and window screen hole size greater than the size of the insect. This outbreak highlights the link between human habitation and ecological dynamics and how climate change factor coupled with behavioural practices had increased the chances of the outbreak. Insufficient awareness underscores the need for community education. Recommendations included targeted awareness programs, minor engineering changes on window screen sizes, and the need for state specific action plan in Himalayan region to tackle such emerging threats to the health system in the future.