Outbreak investigation of acute diarrhea caused by Salmonella among inmates at Prison A, Nathawi District, Songkhla Province, April 22-28, 2024

Abstract

Background: On April 21, 2024, at 09.37 PM, the SRRT team of Klong Hoi Khong Hospital received notification from SAT team of Songkhla Provincial Public Health Office that 65 prisoners of prison A in Nathawi District, had acute diarrhea. Therefore, the joint investigation team investigate the outbreak during April 22–28, 2024 to confirm the diagnosis and outbreak, describe epidemiological characteristics, search for causes and risk factors, and to control the outbreak.

Methods: A descriptive epidemiological study was conducted to identify additional cases of inmates or staff at Prison A who experienced diarrhea (loose or watery stools) accompanied by at least one of the following symptoms: abdominal cramps, headache, fatigue, fever, nausea, vomiting, mucus in stool, blood in stool, tenesmus, or myalgia, between April 18 and 28, 2027. An analytical study using a case-control design was conducted to investigate risk factors along with study of prison environment, food preparation processes, and the drinking water and utility water systems. Environmental samples were collected for laboratory analysis.

Results: A total of 209 individuals met the case definition, all of whom were inmates. The overall attack rate was 12.13% from 1,723 inmantes. Three cases (1.4%) required hospitalization and were all male. The remaining 183 cases (87.56%) were female, and 26 cases (12.44%) were male. The median age was 36 years (range: 20-86 years). Cases were distributed across all wards, with the highest attack rate observed in the female ward (19.69%), followed by Ward 2 (16.32%). No deaths were reported. The most common symptoms were watery diarrhea (77.51%), followed by abdominal cramps (62.20%) and loose stools (55.98%). The outbreak was attributed to Salmonella Montevideo, as confirmed by both rectal swab and fresh stool cultures. This finding is consistent with a common-source, point-source outbreak. The likely source of contamination was the water supply. Risk factors included a raw water source located near a garbage dump, a damaged water storage tank, and a malfunctioning automatic chlorine dispenser one week before the outbreak. Coliform bacteria were detected in drinking and utility water samples, and no residual chlorine was detected.

Summary and Discussion: An outbreak of acute diarrhea caused by Salmonella montevideo was detected among inmates at Prison A, Nathawi district, Songkhla province. The likely source of the outbreak was contaminated raw water used for cooking, cleaning utensils, and drinking. Following the outbreak, bottled water was provided, chlorine was added to the water storage tank, and water was boiled for 15–20 minutes after filtration for drinking, cooking, and cleaning utensils. The outbreak has since subsided, and no new cases have been reported as of May 8, 2027, based on ongoing surveillance.