Eosinophilic meningitis epidemiological data from a national database in Thailand’s Department of Disease Control: a pragmatic, retrospective analytical study
Authors: Khamsai Sittichai , Chotmongkol Verajit , Tiamkao Somsak , Maleewong Wanchai , Limpawattana Panita , Boonsawat Watchara , Sawunyavisuth Bundit , Aekphachaisawat Noppadol , Sawanyawisuth Kittisak 
Published: October 2022

Abstract
Background
Eosinophilic meningitis (EOM) is a rare neurological disease that can be misdiagnosed or underdiagnosed. Based on reported cases in the literature, there have been 2,827 cases worldwide since 1945. There are limited data on the prevalence and trends of EOM in a real-world setting, even in Thailand, the country with the highest prevalence of EOM. Therefore, this study aimed to evaluate the prevalence of EOM and EOM epidemiological data in a real-world setting.

Methods
This was a pragmatic, retrospective analytical study using a national database. We retrieved EOM epidemiological data reported from government hospitals to Thailand’s Bureau of Epidemiology, within the Ministry of Public Health’s Department of Disease Control (DDC), between 2014 and 2019. The study was conducted by retrieving the data of all patients diagnosed with EOM and reported to the DDC. Diagnosis of EOM is made clinically by evidence of eosinophils of 10% or more of the total white blood cells in cerebrospinal fluid. Details of each patient were retrieved from the 506 Report Form, including age, month of reported case, zone of country, occupation, and mortality. Data regarding infection rate in each year and each zone were reported in rate/100,000 population, while data regarding age, month of reported case, and occupation were reported by year. Differences between means of age group, month of reported case, and occupation were tested by one-way analysis of variance (ANOVA). For those factors with significant differences among groups, Bonferroni method was used to compute pairwise differences.

Results
There were 1,083 EOM cases reported in Thailand during the six-year study period. The average annual incidence of EOM was 180.5 cases, or 0.27 cases/100,000 population. The northeast zone had the highest rate, with 0.89/100,000 population. The common age groups were 25–54 years, with the highest rate among the 35–44 age group, with a mean of 38.3 persons/year. These age groups were significantly different from other age groups (F value 39.23; p < 0.001). A relatively high cumulative monthly incidence (> 100 cases) was seen in four months, including January (117 cases), September (103 cases), October (112 cases), and November (103 cases), though these rates were not significantly different from the other months’ rates. Regarding occupation, the top two occupations with EOM diagnoses were farmers and laborers, which were significantly different from other occupations (F value 99.95; p < 0.001). There was no reported case of death during the study period.

Conclusion
EOM is common in Northeast Thailand among people of working age. The disease can be found throughout the year but is more common in the last quarter of the year. Farmers and laborers have the highest infection rate. To better understand the burden and outcomes of EOM, a national EOM reporting system with a better reporting form is required in endemic countries. Such a report form should include more details on risk exposure, symptoms, signs, treatment, and outcomes.