Analysis of a tuberculosis outbreak in an office: Hokkaido, Japan, 2019-2020.

Background: In August 2018, a male worker (Pt1) in an office was diagnosed with smear-positive pulmonary tuberculosis (TB). This study aims to characterize the cases found in the TB outbreak in the office.

Methods: The risks of TB disease or infection were compared among the staff members by seating locations.

Results: A total of 116 current and ex-staff members were investigated, among whom 13 patients with active TB, including Pt1, and 20 with latent TB infection were found by the end of 2020. One-third of the seating groups located at one end of the office that Pt1 belonged to had the highest risk of TB disease (30.8%, 95% confidence interval [CI]: 14.3%-51.8%) and infection (61.5%, 95% CI: 40.6%-79.8%) with a high relative risk of TB infection (6.2, 95% CI: 2.0-18.8) compared to another one-third of the seating groups at the other end of the office that had the lowest risk of active TB (0%, 95% CI: 0%-11.6%) and TB infection (10.0%, 95% CI: 2.1%-26.5%).

Conclusion: The seating groups that Pt1 belonged to had the highest risk of TB disease and infection because the staff members in the groups were exposed to the air containing TB bacilli from Pt1. Local health offices should initiate active case finding using chest X-rays as soon as they are notified of a sputum smear-positive TB case if the delay of the diagnosis is longer than three months.