Outbreak investigation of influenza A H1N1 in a prison in Pitsanuloke province, Thailand, July–September 2018

Abstract

Background: On 6 August 2018, the Bureau of Epidemiology, Department of Disease Control was notified of several cases of suspected influenza in a prison in Pitsanuloke province. The outbreak investigation was carried out to confirm the outbreak, verify diagnosis, describe epidemiologic characteristics, determine risk factors and recommend preventive and control measures during 8-9 August 2018 and follow-up the outbreak situation after measures during 12-13 September 2018.
Methods: The investigation included situation analysis of influenza in the area from the disease surveillance, active case finding in the prison, laboratory examination, environmental study and review of influenza-like illness from the prison health care center. A retrospective cohort study was carried out to identify possible risk factors. Data were analyzed and preventive and control measures were implemented in the prison.
Results: A total of 450 influenza cases were identified. Of them, 448 were inmates and 2 (1 male and 1 female) were prison officers. Two cases died, giving the case-fatality rate of 0.44%. The age of the cases ranged 17– 78 years old, with a median of 33 years old. The clinical manifestations were fever (100%), myalgia (100%), headache (84.82%) and cough (74.55%). Of the 35 cases with viral laboratory examination, 17 were found to have influenza A (H1N1) by real time RT-PCR. Risk factors significantly associated with the disease by multiple logistic regression were sharing a glass ( adjusted odds ratio = 1.42, 95% CI = 1.11– 1.81) , close contact with a case ( adjusted odds ratio = 3.23, 95% CI = 2.55– 4.10) and having an underlying disease (adjusted odds ratio = 2.14, 95% CI = 1.59– 2.89).
Conclusion: This outbreak was caused by influenza A ( H1N1) . Factors affecting the outbreak might be delay in outbreak detection, no patient isolation during the beginning of outbreak, overcrowded condition in the prison and poor personal hygiene. Preventive and control measures included patient isolation, screening for early detection of suspected influenza, reduction of close contact with a case and screening for the disease in persons who visit the inmate. The outbreak curtailed rapidly after implementation of preventive and control measures. The last case was detected on 9 September 2018.