An outbreak investigation of Influenza A H3N2 in a battalion, Surat Thani province, Thailand, August 2014

Abstract

On 14^th August 2014 , Bureau of Epidemiology (BOE) was notified of a suspected influenza outbreak in a battalion by a physician in a military hospital in Surat Thani province. BOE and local Surveillance and Rapid Response Team conducted investigation during 15 - 17 August 2014 to confirm the diagnosis, describe the epidemiological characteristic, identify risk factors and recommend control measures. We conducted active case finding in the battalion and reviewed medical records in the military hospital following the BOE Influenza-like Illness (ILI) case definitions. And we conducted environmental survey, interviewed conscripts and trainers and observed their activities, interviewed health officers in the military hospital and provincial health officers on the actions taken. Totally, 136 suspected cases were identified from 309 conscripts (Attack rate 44%). The outbreak could be divided into two waves. The first wave occurred during 1 - 16 August 2014 and then the second wave occurred during 17-21 August 2014. The highest attack rate appeared in the Newly Recruit Company (Attack rate 63%). Nineteen of 21 (90%) throat swabs were positive for influenza A H3N2 by RT-PCR. No isolation of cases and failure to exclude cases from training in the first week might result in rapid spread of the disease in the battalion. The hypothesis was made and a retrospective cohort study was conducted among new conscripts using self-administered questionnaire. Multivariate analysis employing logistic regression model was performed to identify risk factors. Statistically significant risk factors identified were sharing glass, sharing spoon and having bed close to a case’s bed. Control measures were implemented, cases were isolated and excluded from training, drinking glasses were separated for each individual, health educations was given to stop sharing utensil, and promote hand washing and mask using.