Malaria in an informal settlement of a socioeconomically disadvantaged population in Rajasthan, a non-endemic state of India, 2024: an epidemiological investigation

In 2024, there were an estimated 3900 malaria deaths in the World Health Organization’s South-East Asia Region (WHO-SEAR), of whom India accounted for 89%. In November, 2024, three suspected malaria deaths were reported from an informal settlement near Village A, Sirohi district, Rajasthan, a malaria non-endemic Indian state with malaria cases < 1 per 1000 population. We investigated to confirm the cause of these deaths, search for additional cases, describe the epidemiology, and identify contributing factors. We conducted verbal autopsies for the three deceased children. A suspected case was defined as fever between October 11th–December 10th, 2024, in the settlement resident; a malaria case was a suspected case that tested positive for Plasmodium falciparum (Pf) or P. vivax (Pv) via rapid antigen test or blood smear microscopy. The settlement was surveyed house-to-house, to identify suspected cases. Identified suspected cases were interviewed to collect demographic and clinical data, assess exposures; and tested to confirm malaria. We identified larval breeding sites, and captured larvae and adult mosquitos. Blood smear preparation by field workers was observed and microscope quality was assessed. All three deceased children (aged two, five, and 11 years) were siblings with fever lasting 6–10 days. Two died at home untreated; one was hospitalized and confirmed as Pf , and died in hospital. The settlement had 752 residents in 137 households. Among 752 residents, 41 suspected cases were identified, among whom 21 were confirmed (18 Pf , 3 Pv ) (attack rate: 2.8%); six needed hospitalization (all Pf ). There were three deaths, with case fatality rate 14.3 (3/21)%. Larval breeding was found in six of 160 water bodies. Of 278 adult Anopheles mosquitoes collected, Anopheles subpictus (29.3%), An. stephensi (20%), An. fluviatilis (19%), and An. culicifacies (12.5%) were predominant. Most (95%) cases slept outdoors without mosquito nets. Microscopy facilities were nonfunctional, and incorrect slide-preparation practices were observed in the nearest health facility. The settlement was unmapped and excluded from routine surveillance and control activities. A laboratory-confirmed seasonal increase in malaria incidence, leading to three deaths, occurred in an informal settlement near Village A, probably due to outdoor sleeping habits of cases, in proximity to mosquito breeding sites, absence of surveillance and control activities, and limited diagnostic capacity of the health facility, delaying diagnosis. We trained the field staff in slide preparation, conducted source-reduction and community-awareness activities, and recommended strengthening laboratory diagnostics.