An outbreak investigation of influenza in a university, Nakhon Ratchasima Province, Thailand, 8–17 August 2018

Abstract

Background: On 7th August 2018, the Bureau of Epidemiology was notified that the cluster of influenza cases were found in University A, Nakhon Ratchasima Province. Many of them joined freshman activity. The objectives were to confirm the outbreak and diagnosis, to describe the epidemiological characteristics of the outbreak, to identify risk factors of the outbreak and to recommend prevention and control measures.
Method: We reviewed medical records and interviewed cases. Active case finding was performed. Suspected case was defined as a student or officer in University A who had fever and myalgia and had at least one of the following symptoms; headache, cough, sore throat, fatigue, nasal congestion and conjunctivitis during 15th July to 17th August 2018. Probable case was suspected case who had positive for rapid influenza diagnostic test. Confirmed case was suspected or probable case who had positive laboratory confirmation. Nasopharyngeal swab was collected among suspected or probable cases to perform confirmatory test by reverse transcription polymerase chain reaction. For analytic study, case was defined as the first–year student who met probable and confirmed case and control was defined as the first–year student without any symptoms in the case definition. Case–control study (2:1) with multiple logistic regression analysis was conducted. Environmental and personal hygiene study was performed.
Results: We found 169 cases (confirmed case was 6.51 percent, probable case was 28.99 percent and suspected case was 64.50 percent). Most of cases were the first–year student with specific attack rate of 4.68%. We collected specimens from 15 suspected case and 13 specimens were positive for influenza A (8 specimens for H1N1/2009, 4 specimens for H3N2, and 1 specimen for both). For analytic study, there were 71 cases and 155 controls. Multivariable analysis revealed significant association between having roommate diagnosed as influenza and the influenza infection (Adjusted odds ratio = 2.93, 95% confident interval = 1.08–7.94).
Conclusion: There was influenza A H1N1/2009 and H3N2 outbreak affected 169 students (crude attack rate was 1.69 percent). Important risk factor was having roommate diagnosed as influenza. Early screening and improve personal hygiene should be implemented.