ICMR study identifies well water as major risk factor for amoebic meningoencephalitis in Keralam

The first joint field-level study by the Keralam Health Department and experts from ICMR’s National Institute of Epidemiology in Chennai to describe the epidemiology of amoebic meningoencephalitis (AME) cases reported in Kerala in 2025 has identified exposure to natural water bodies and the use of non-chlorinated water for bathing and other domestic purposes as significant risk factors, providing the first epidemiological evidence from the State on potentially modifiable exposures linked to amoebic meningoencephalitis.The case-control study is the first scientific proof of the questionable quality of well water in Keralam, on which a significant section of the population depends for bathing and other domestic use.It has already been well explained by the scientific community that certain risky behaviours — exposure to natural water bodies (especially diving into water and snorting water into the nostrils), a history of previous facial or nasal injury, and entering natural water bodies when there are ulcers or skin wounds — predispose one to AME caused by Acanthamoeba, which can enter the body through tissue or the respiratory tract.“The finding that the use of non-chlorinated water, or well water, for domestic purposes is independently associated with AME caused by Acanthamoeba is quite relevant for Kerala, where only a tiny fraction of the population has access to chlorinated, safe, piped water supply. Our study results showed that people using well water for bathing or washing their face had 2.95 times higher odds of getting AME,” points out R. Aravind, Head of Infectious Diseases, Thiruvananthapuram Government Medical College, and one of the key researchers involved in the study.“The estimated population attributable fraction (PAF) was 34.2%. This means that 34.2% of the cases of AME caused by Acanthamoeba in the population would not occur if non-chlorinated well water, as a specific risk factor, was removed,” Dr. Aravind pointed out.(PAF is an epidemiological measure that estimates the proportion of disease cases in a population that would not occur if a specific risk factor were removed.)It should be noted that domestic water use referred to activities involving direct contact with the face, head, skin, or body, such as bathing or washing the face or hair, and did not refer to ingestion.Many households in Kerala depend on individual or public wells. Heavy rainfall, flooding, sewage contamination, organic matter, and algal growth might contribute to the contamination of, or proliferation of free-living amoebae (FLAs) in, poorly maintained wells.This case-control study is the highest level of scientific evidence that water quality is going to be a key public health issue in which the State will have to invest in the immediate future. Water quality surveillance, along with periodic chlorination and maintenance of wells, has to be a year-round activity through local self-governments so that the risk of people contracting AME can be minimised.In a State where there are a large number of water bodies, the focus of public health messaging about AME should be on reducing high-risk exposures, particularly during the monsoon and post-monsoon period, along with routine chlorination of domestic water sources.The study, “Epidemiology of and Risk Factors for Amoebic Meningoencephalitis, Kerala 2025”, published in the latest issue of Emerging Infectious Diseases, the journal of the US Centers for Disease Control and Prevention, analysed 159 AME cases reported in Kerala between January 1 and November 11, 2025. Of these, 76 were confirmed by real-time PCR and 83 by microscopic examination of cerebrospinal fluid.Among the PCR-confirmed cases, 67 (88.2%) were caused by Acanthamoeba species and nine (11.8%) by Naegleria fowleri.This is significant because popular perception, and even international media attention, centred on the “epidemic” of “brain-eating amoeba” (N. fowleri) infections in Kerala, when, in fact, an overwhelming majority of AME cases in the State in 2025 were granulomatous amoebic encephalitis caused by Acanthamoeba.Among the 159 case-patients, 41 died, giving a case fatality rate of 25.8%. Seventeen of the 67 patients with PCR-confirmed Acanthamoeba infection died (25.4%), while four of the nine N. fowleri patients died (44.4%).The researchers noted that between 2016 and 2024, Kerala had reported only 45 AME cases and 15 deaths. Increased clinical awareness, wider availability of molecular diagnostics, and improved surveillance could have contributed to the sharp increase in laboratory-confirmed AME cases in 2025.To identify possible risk factors, the researchers conducted a matched case-control study restricted to 43 PCR-confirmed Acanthamoeba patients and 129 apparently healthy controls from Thiruvananthapuram, Kollam, Kozhikode, and Malappuram. Three controls were selected for each case and matched for age, sex, and place of residence.Exposure to natural water bodies — swimming or diving in ponds and canals during the preceding three months, especially among persons with a history of maxillofacial injury or nasal surgery — was associated with 4.7 times higher odds of disease.Exposing skin wounds or ulcers to natural water bodies had one of the strongest associations with AME. The odds of AME in this group were 25.4 times higher. This is consistent with the known ability of Acanthamoeba to enter through breaks in the skin and subsequently disseminate to the central nervous system.Public health communication should therefore specifically advise persons with previous facial or head injuries, and those with wounds or skin ulcers, against entering natural water bodies, especially during the monsoon and post-monsoon season.The researchers make an important distinction: while the entry of contaminated water through the nose is an established route of transmission for N. fowleri, it has not been established as a route of transmission for AME caused by Acanthamoeba.Although Acanthamoeba AME has traditionally been associated with immunocompromised individuals, in the Kerala study, most PCR-confirmed Acanthamoeba AME cases did not have documented immunocompromising conditions, according to records.The researchers say that host susceptibility remains important, but it cannot by itself explain the pattern of AME seen in Kerala.They also make a clear distinction that the associations between Acanthamoeba AME and exposure to natural water bodies or non-chlorinated water are epidemiological associations and do not prove that water exposure led directly to neuroinvasion. Further environmental, clinical, and microbiological studies would be needed to determine whether these associations reflect a route through which the disease was acquired.Lower socioeconomic status was associated with AME in this study, which might influence the behavioural exposures identified by the researchers. Low socioeconomic status could affect access to safe domestic water and increase reliance on non-chlorinated wells. This is also why most AME cases are reported by public hospitals.Risk communication on AME should therefore prioritise socioeconomically vulnerable communities, the study notes.