Outbreak investigation of influenza type B in a school, Phrai Bueng District, Sisaket Province, January 10–February 2, 2025

Abstract

Background: On January 22, 2025, three influenza-like illness cases at OPD were identified through the 506-surveillance reporting system of Phrai Bueng Hospital. All of them were students from the same school in Phrai Bueng District, Sisaket Province. Many contact cases were also found. The operation team of Phrai Bueng District then conducted the outbreak investigation during January 22–29, 2025 in order to confirm the diagnosis and control the outbreak.

Method: A descriptive epidemiological study was conducted to assess the influenza situation in Sisaket Province and Phrai Bueng District. Collecting patient medical history. Interviewing students as well as school personnel. Finding more active case by using the suspected case definition : Students of class 4–5 level at a school in Samrong Phlan Subdistrict and children aged 6–15 years living in Villages no.1 and no.13, Samrong Phlan Subdistrict, Phrai Bueng District, who presented with at least one of the following symptoms; fever, cough, rhinorrhea, headache, and vomiting. During 10 January-2 February 2025. The environmental study was also conducted. The laboratory study was performed by collecting specimens tested for influenza viral RNA by using Realtime reverse transcription polymerase chain reaction (Realtime RT-PCR) method.

Results: The total of 17 cases met the clinical case definition for influenza-like illness. 14 cases were school children and 3 cases were from the community. Mean age was 10 years. Male to female ratio 1:1.42. Influenza A/B Antigen Rapid Tests were positive for 3 Influenza B cases and Real-time RT-PCR showed Influenza B viral RNA in 2 cases. All patients presented with fever (100%), followed by rhinorrhea (97.44%) and cough (88.89%). Identified risk factors contributing to the outbreak comprised closed contact with individuals exhibiting symptoms, as well as the consumption of food or beverages from shared utensils or containers.

Conclusion and Discussion: The outbreak pattern was indicative of a propagated source. Shared activities within the school and community were identified as key contributing factors to the spread of Influenza B. The transmission appeared to begin within a classroom and subsequently extended to other classes, including households, and the community. Following the implementation of disease control measures, the last reported case occurred on January 27, 2025. Continued surveillance for 14 days thereafter revealed no new cases.