An Outbreak Investigation of influenza in an Office, Mueang District, Nakhon Ratchasima Province, Thailand, April–May 2019

Abstract

Background: On 21 April 2019, an office building in Nakhon Ratchasima developed a cluster of 15 influenza–like illness (ILI) cases. There were at least 6 patients had been diagnosed with influenza by medical doctors. The Division of Epidemiology conducted a joint investigation during 22–24 April 2019.
Method: Descriptive study was performed included reviewing the influenza situation, reviewing the medical record, active case finding in the office, laboratory examination, environmental study, activities and behaviours related to the outbreak. Retrospective cohort study and multiple logistic regression analysis were used to identify factors associated with the illness.
Results: A total of 32 influenza cases were identified, attack rate 16.67%, 1 patient with severe pneumonia, no deaths. The median age was 31.5 years (ranged 24–41 years). The clinical manifestations were fever (100%), cough (81.25%) myalgia (71.88 %), sore throat (68.75%), headache (65.63%) runny nose (62.50) phlegm (56.25) and weakness (56.25). Of the 7 cases with viral laboratory examination, 5 were found to have influenza B by Real– Time PCR. All 5 cases were positive influenza B Victoria lineage by gene sequencing. Based on multiple logistic regression analysis, the risk factors significantly associated with this outbreak included people who worked in the same section with person with influenza like Illness (adj OR = 12.89, 95% CI = 3.60–43.74) and sharing drinking glasses with patients (adj OR = 15.56, 95% CI = 1.05–230.71). The environmental study results found that the employees were seated close together, used ceiling cassette air conditioner, shared tools or office equipment and common passenger elevators. Persons with ILI still came to work and had activities with others without wearing masks.
Conclusions and discussions: This outbreak was caused by influenza B in the Office. Factors associated with the illness included working in the same section with person with ILI, and sharing drinking glasses with patients. Important preventive and control measures included giving knowledge about influenza and emphasizing prevention, disease control, hygiene, wearing a mask, washing hands, cleaning and disinfect for employees, in addition to strengthening ILI surveillance in the office.