An outbreak investigation of mixed influenza A and B in a military training unit, Meuang Nakhon Ratchasima district, Nakhon Ratchasima Province, Thailand, 10 May – 1 June 2016

Abstract

Background: On 9 May 2016, Surveillance and Rapid Response Team was notified by Suranaree Camp Hospital about a cluster of influenza-like illness among draftees at a military division stationed in the province. We started outbreak investigation with aim to confirm diagnosis and outbreak, to identify risk factors of the outbreak and to recommend for control and prevention measures during 10 May – 1 June 2016.
Methods: We studied descriptive study by active case finding at the military camp. The case definition was a draftee or military officer who had fever with one of the following cough or sore throat or myalgia from 20 April – 10 June 2016. Laboratory confirmation was performed by RT-PCR for influenza virus. Retrospective cohort study was carried out to determine the risk factors of the outbreak and environment in the camp was also surveyed.
Results: Total 119 cases were met case definition in both two camps and overall attack rate was 41.60%. Forty eight (48) cases were located in camp A with attack rate was 50.5%. Seventy one (71) cases were identified in camp B with attack rate was 37.2%. Laboratory investigation revealed 8 cases in camp A were positive influenza B (61.53%) and one case in camp B was positive influenza A (20%). Dining without transferred spoon with the case (RR = 1.91, 95% CI 1.41-2.60), sharing towels with the case (RR = 2.22, 95% CI 1.64-2.99) and attending service close to the case (RR. = 1.98, 95% CI 1.46-2.68). Multiple logistic regression revealed dining without transferred spoon with the case (adjusted OR = 4.45, 95% CI 1.56-13.17) and attending service close to the case (adjusted OR = 4.33, 95% CI = 1.22-14.68).
Conclusions: Mixed influenza A and B was confirmed in the military camps. Most of the case was military draftees. The strongest risk factors were dining without transferred spoon and attending service close to the case. We intervened the risk factor by promoting use of transferred spoon and separating ill draftees and non-ill during attending military service. All draftees were promoting personal hygiene and sanitation.