Outbreak investigation of influenza A/H3N2 in a prison, Lop Buri Province, October - December 2019

Abstract

In October 2019, an influenza outbreak occurred in a prison in Lop Buri Province. This outbreak investigation aimed to confirm the diagnosis and outbreak, describe the distribution of disease by person, time and place, and to recommend disease preventive and control measures. The investigation included review of patients’ medical record from the prison health care center, interviewing the patients and health care personnel of the prison, active case finding in the prison, and laboratory examination of the patients’ specimens for influenza diagnosis. Of 3,591 prisoners, 179 had influenza, giving the attack rate of 4.98%. None died in this outbreak. The first case had onset of the disease on 15 October 2019 and the last case was on 20 November 2019. All the cases were male prisoners. No cases were found among the prison officers. The age of the cases ranged between 19-71 years, with a median of 33 years old. The clinical manifestations were fever (100.00%), headache (91.06%) and cough (77.09%). Of the 10 cases with viral laboratory examination, all were found to have influenza A (H3N2) by real-time RT-PCR. Among the prisoners, 569 had influenza vaccination in May 2019 (before the outbreak). The attack rate among the vaccinated prisoners was 2.46% compared to 5.46% among the unvaccinated, giving the vaccine effectiveness of 54.95%. This outbreak was caused by influenza A (H3N2). Risk factors for disease spread might be performing activities together and sleeping in the same room. The outbreak curtailed after implementation of preventive and control measures. No additional cases were found after 20 November 2019.