A tuberculosis contact investigation involving a large number of contacts tested with interferon-gamma release assay at a nursing school: Kanagawa, Japan, 2012
10.5365/wpsar.2018.9.1.001
- Author:
Masako Tasaka
1
;
Tamae Shimamura
;
Mami Iwata
;
Takahiro Toyozawa
;
Masaki Ota
Author Information
1. Kanagawa Prefectural Institute of Public Health, Kanagawa, Japan
- Publication Type:Journal Article
- Keywords:
Epidemiology;
Contact investigation;
Interferon-gamma release assay;
Disease outbreak;
Tuberculosis
- From:
Western Pacific Surveillance and Response
2018;9(3):4-8
- CountryWHO-WPRO
- Language:English
-
Abstract:
In May 2012, a teacher of a nursing school with about 300 staff members and students in Japan was diagnosed with sputum smear-positive pulmonary tuberculosis (TB), leading to an investigation involving nearly 300 contacts. We describe the contacts’ closeness to the index TB patient and the likelihood of TB infection and disease.
A case of TB was defined as an individual with positive bacteriological tests or by a physician diagnosis of TB. A latent TB infection (LTBI) case was defined as an individual who had a positive interferon-gamma release assay (IGRA).
A total of 283 persons screened with IGRA were analysed. Eight persons (2.8%, 95% confidence interval [CI]: 1.2–5.4) tested positive by IGRA; one student who had intermediate (less than 10 hours) contact with the index patient was found to have pulmonary TB by chest X-ray. The positivity in IGRA among staff members with very close contact with the index patient (4 of 21, 19%, 95% CI: 5.4–42%) with a statistically significant relative risk of 17 (95% CI: 2.0–140) was high compared with that of the intermediate contacts (1 of 88, 1.1% [95% CI: 0.028–6.2]). There was a statistically significant trend in the risk of TB infection and closeness with the index patient among the staff members and students (P < 0.00022).
In congregate settings such as schools, the scope of contact investigation may have to be expanded to detect a TB case among those who had brief contact with the index patient.
