An outbreak investigation of Influenza B in high school A, Yasothon Province, Thailand, 19–22 February 2014

Abstract

Background: On 19^th February 2014, The Surveillance Rapid Team (SRRT) of Yasothon Provincial Health Office was notified about a cluster of influenza–like illness (ILI) in a high school, Yasothon Province. An outbreak investigation was conducted in order to confirm a diagnosis, identify risks factors of outbreak and to implement outbreak control and prevention measure.
Method: Descriptive and retrospective cohort study were carried out by Interviewed and conducted active case finding program in the high school, an environmental survey was also done. Laboratory confirmation was done by RT–PCR in throat swab. Multiple logistic regressions were used to identify independent risk factors.
Results: There were 524 students in the school, 133 cases were met case definition with attack rate of 25.4%. Nearly half (41.5%) of those were male. Median age was 15 years (range 12–19 years). Cases were identified in all classrooms in the school. The most common of clinical presentation was cough (7 8 . 4 %), headache (6 1 . 2 %), mucus (59.7%), sore throat (56.7%), muscle pain (46.3%) and fever (28.4%) respectively. Influenza B (3/5) was positive RT–PCR. Multiple logistic regression revealed 2 independent risk factors included dining together with the case (Adjust Odds Ratio [adj.OR] = 2.7, 95%CI 1.2–6.0) and having symptomatic peer (adj.OR = 2.1, 95%CI 1.1–3.9). The control measure was health education, an advising all suspected to keep personal hygiene including mask wearing, hand washing and isolation.
Discussions and Conclusions: This outbreak was caused by Influenza B. The closed contact with the case was the strong risk factors. Mild severity of influenza B made a wide spreading easily. After follow up for 14 days, there was no additional case in the school. The school was encouraging to give health education, screening Influenza– like illness and early isolation among the students particularly in winter.