[EXAMINATION OF TUBERCULOSIS OUTBREAK INDEX CASES IN OSAKA CITY]

To analyze tuberculosis outbreak index cases in order to improve preventative measures.

Outbreaks reported in Osaka City between 2008 and 2014 were investigated. The index cases were examined according to category group, sex, age, chest radiograph findings, sputum smear examination, patient delay, doctor delay, total delay in case finding, and adherence to regular health examinations. As controls, 467 patients in Osaka City with newly registered sputum smear-positive pulmonary tuberculosis in 2011 were included.

Thirteen outbreaks occurred. The group categories included enterprises (9 outbreaks), preparatory schools (2), a junior high school (1), and other (1). The group of index cases consisted of 12 men (92.3%) and one woman (7.7%), with a mean age of 39.1 years; 11 (84.6%) were 30 to 50 years of age. Their ages ranged from 15 to 54 years. Of the control group of patients with sputum smear-positive pulmonary tuberculosis, 69.2% were 60 years or older, with a mean age of 65.4 years. These results suggest that the index case group was significantly younger (p < 0.001). There were ten cases (76.9%) of patient delay (initial visit 2 months or more after onset), and 8 (61.5%) of total delay (diagnosed 3 months or more after onset). These rates were significantly higher than those in the control group (p < 0.001). There were regular health examinations in four cases; among those, one did not see a doctor and another did not receive further examination. Chest radiographs revealed cavities in 12 cases (92.3%). All sputum smears were positive, with grades of 1 + in one case (7.7%), 2 + in two cases (15.4%), and 3 + in 10 cases (76.9%). These cases had a significantly higher rate of smear positivity than those in the control group (p < 0.001).

The index cases were predominantly male, in their prime, and had higher infectivity rates. These findings suggest the importance of preventing delays in case findings and receiving regular and adequate health examinations.