Outbreak investigation of influenza B in a prison, Chaiyaphum Province, June 2023

Abstract

Influenza is an acute respiratory disease caused by influenza virus infection. While symptoms may be mild in some cases, severe manifestations can occur, especially in crowded prison settings. On June 13, 2023, Chaiyaphum Hospital received a report of a significant number of inmates displaying suspected influenza symptoms in a local prison in Chaiyaphum province. Subsequently, an on-site disease investigation and control measures were initiated to curb the outbreak. This study employed analytical epidemiology to confirm the diagnosis, describe the epidemiological characteristics, identify risk factors, and provide recommendations for preventive and control measures. The investigation, conducted between June 13 and 24, 2023, integrated epidemiological surveillance data, additional patient searches, environmental surveys within the prison, and laboratory analysis. An analytical epidemiological study utilizing an unmatched case-control study was conducted to identify potential risk factors. The data were analyzed, and preventive and control measures were subsequently implemented in the prison. The results revealed that 300 individuals met the criteria for influenza, comprising 297 male inmates and 3 male correctional officers, with an overall attack rate of 21.25%. Most affected individuals were aged 19-65 years, with a median age of 35 years. The majority exhibited mild symptoms, including cough (86.00%), myalgia (78.33%), and headache (73.66%). Among the 49 nasopharyngeal swabs tested using Rapid Influenza Diagnostic Tests (RIDT), 27 were positive for influenza B. Additionally, 4 out of 5 nasopharyngeal swabs tested using real-time RT-PCR were positive for influenza B. From this investigation, two significant risk factors for disease transmission were identified, including sharing water bottles and glasses with others (odds ratio = 2.87, 95% CI: 2.06-4.00) and engaging in conversations with individuals experiencing flu-like symptoms (odds ratio = 1.39, 95% CI: 1.01–1.94). This investigation has confirmed that the outbreak was caused by influenza B. In response, rigorous measures have been implemented to control and prevent the spread of the disease, such as providing personal hygiene education to both inmates and correctional officers. It is strongly recommended that individuals use face masks to cover their mouth and nose during coughing, sneezing, or interactions with others. Furthermore, sharing water bottles and glasses with others is strictly prohibited as an additional preventive measure.