Cluster of 19 cases of eosinophilic meningitis due to Angiostrongylus cantonensis in Lifou, New Caledonia: an outbreak investigation.

backgroundEosinophilic meningitis due to Angiostrongylus cantonensis (AC) is an emerging parasitic disease worldwide but remains endemic in the Pacific region. In New Caledonia, sporadic cases occur each year, and the route of transmission is often unclear. In January 2023, an unusual cluster of three cases occurred in a village on Lifou Island following week-long community festivities, leading to an epidemiological investigation to determine the outbreak scope, the source of contamination, and inform public health interventions.

methodsWe conducted a retrospective epidemiological and environmental investigation in one month after the suspected exposure. Cases were defined according to international criteria and classified as confirmed, probable, or suspected. Clinical data, attendance at the festivities and food exposures were collected from medical records and interviews. Environmental observations focused on potential contamination sources in food preparation areas. Serological analyses were performed in symptomatic and asymptomatic exposed individuals. Descriptive statistics were used to summarize demographic, clinical, and exposure characteristics.

resultsNineteen cases were identified, including three confirmed and sixteen suspected cases; no probable cases were identified. Headache was the predominant symptom, often associated with vomiting or paresthesias. All cases attended festivities on December 27, 2022 suggesting a common exposure during that day. The median incubation period was 3 weeks (IQR: 2-4). Two exposure hypotheses were identified: beverages diluted with rainwater and contamination of blended fruit juice. Environmental investigations revealed rats and gastropods around rainwater reservoirs and food preparation areas, including on utensils left to dry outdoors. No AC DNA was detected in water samples. Serology for AC was positive in all confirmed cases (3/3), in 13 of 14 tested suspected cases, and in all ten exposed asymptomatic individuals tested 9 months after the outbreak.

conclusionsThis investigation highlights the diagnostic and epidemiological challenges of neuroangiostrongyliasis in endemic areas, where mild presentations often remain unconfirmed and where the value of serological testing is limited by the lack of baseline seroprevalence data. The findings support the hypothesis of accidental incorporation of a heavily infected gastropod into blended fruit juice during preparation, potentially facilitated by open-air kitchen practices in rural Pacific settings.