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

The first joint field study by the Kerala Health Department and experts from the ICMR National Institute of Epidemiology, Chennai, describing the epidemiology of amoebic meningoencephalitis (AME) cases reported in Kerala in 2025, identified exposure to natural water bodies and use of non-chlorinated water for bathing and other domestic purposes as the first significant risk factors associated with exposure to the state’s outbreaks, providing the first significant risk factors associated with the epidemic. amoebic meningoencephalitis.

The case-control study is the first scientific evidence of the dubious quality of well water in Kerala, on which a significant portion of the population depends for bathing and other domestic use.

It is already well understood by the scientific community that certain risk behaviors—exposure to natural bodies of water (particularly diving into water and blowing water into the nostrils), a history of previous trauma to the face or nose, and entering natural bodies of water in case of ulcers or skin wounds—predispose a person 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 to Kerala, where only a small proportion of the population has access to chlorinated, safe, piped water. The results of our study showed that people using well water for bathing or washing their faces were 2.95 times more likely to experience RAME, RAME,” says Aindious. 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 AME cases caused by Acanthamoeba in the population would not have occurred if non-chlorinated well water was removed as a specific risk factor,” pointed out Dr. Aravind.

(PAF is an epidemiological measure that estimates the proportion of disease cases in a population that would not occur if a particular risk factor were removed.)

It should be noted that household 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 can contribute to the contamination or proliferation of free-living amoebae (FLA) in poorly maintained wells.

This case control study is the highest level of scientific evidence that water quality will be a key public health issue in which the state will need to invest in the near future. Water quality surveillance, along with periodic well chlorination and maintenance, must be a year-round activity through local governments to minimize the risk of people contracting AME.

In a state with a large number of water bodies, public health reporting on AME should focus on reducing high-risk exposures, especially during monsoon and post-monsoon, along with routine chlorination of domestic water sources.

The study, “Epidemiology and Risk Factors of Amoebic Meningoencephalitis, Kerala 2025,” published in the latest issue of Emerging Infectious Diseases, a journal of the US Centers for Disease Control and Prevention, analyzed 159 cases of AME reported in Kerala between January 1 and November 11. microscopic examination of cerebrospinal fluid.

Among 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, has focused on an “epidemic” of “brain-eating amoeba” (N. fowleri) infections in Kerala, when in fact the vast majority of AME cases in the state in 2025 were granulomatous amoebic encephalitis caused by Acanthamoeba.

Of the 159 patients, 41 died, giving a mortality rate of 25.8%. Seventeen of 67 patients with PCR-confirmed Acanthamoeba infection died (25.4%), while four of nine patients with N. fowleri died (44.4%).

The researchers noted that between 2016 and 2024, Kerala reported only 45 cases of AME and 15 deaths. Increased clinical awareness, wider availability of molecular diagnostics, and improved surveillance may have contributed to the sharp increase in laboratory-confirmed AME cases in 2025.

To identify possible risk factors, the researchers conducted a case-control study limited 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 were matched for age, sex, and place of residence.

Exposure to natural bodies of water—swimming or diving in ponds and canals in the previous three months, especially in those with a history of maxillofacial trauma or nose surgery—was associated with a 4.7-fold higher likelihood of the disease.

Exposure of 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 penetrate skin cracks and subsequently spread to the central nervous system.

Therefore, public health communications should specifically warn people with previous facial or head injuries and people with wounds or skin ulcers not to enter natural water bodies, especially during the monsoon and post-monsoon seasons.

The researchers make an important distinction: while nasal entry of contaminated water 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, the majority of PCR-confirmed Acanthamoeba AME cases did not have documented immunocompromising conditions.

The researchers say host susceptibility remains important but alone cannot explain the AME pattern observed in Kerala.

They also clearly distinguish that associations between Acanthamoeba AME and exposure to natural water bodies or non-chlorinated water are epidemiologic associations and do not demonstrate that exposure to water directly led to neuroinvasion. Additional environmental, clinical, and microbiological studies would be needed to determine whether these associations reflect the route by which the disease was acquired.

Lower socioeconomic status was associated with AME in this study, which could affect the behavioral exposures identified by the researchers. Low socioeconomic status could affect access to safe potable water and increase reliance on non-chlorinated wells. This is also why most AME cases are reported by public hospitals.

Communication about AME risks should therefore prioritize socioeconomically vulnerable communities, the study says.