Analysis of 605 tuberculosis outbreaks in Japan, 1993-2015: time, place and transmission site.

Since 1993, reports on tuberculosis (TB) outbreaks have been collected in Japan; however, there has never been an overall analysis of these TB outbreaks. We aim to provide one here. The TB outbreak data were obtained from the Ministry of Health, Labour and Welfare and are described in terms of time, place and transmission site. The average number of TB cases and latent tuberculosis infection (LTBI) were compared by the transmission site. Some 605 TB outbreaks with 3491 TB cases were reported in 1993-2015 with an increasing trend (r = 0.45), during which time 728 777 TB cases were reported nationwide. On an average, TB outbreaks occurred more often in April to May (5.5 outbreaks per 2 months) than in December to January (3.4). The most common transmission sites were workplaces (n = 255), followed by health facilities (n = 144), schools (n = 60) and welfare facilities (n = 48). Psychiatric hospitals and nursing homes had the highest average number of TB cases per outbreak (8.5 each), whereas schools and prisons had the highest numbers of LTBI cases (29.1 and 38.9, respectively). Countries, particularly those that have resources to investigate TB outbreaks, should collect and analyse findings of TB outbreaks, as it informs surveillance systems and eventually strengthens general health systems.