[Epidemiological significance of patients with extra-pulmonary TB--a study of 10,082 patients with tuberculosis].

Objectives: To elucidate the epidemiological significance of patients with extra-pulmonary TB.
Subjects and Methods: The subjects of this retrospective study were 10,088 TB patients registered in Aichi prefecture between 1989 and 2003. Of these, 8,629 patients had pulmonary TB and 1459 had extra-pulmonary TB. All registration files were reviewed to identify the epidemiological links of patients. When linked patients with an interval of less than 10 years between registrations were found, the earlier registered case was considered the primary or index case, and the other patients were regarded as secondary cases. The index case rate (ICR) for a category of patients was defined as follows: ICR=NI/NA, where NA: number of TB patients in a category A, and NI: number of index cases in category A.
Results: The ICR for the 1,459 extra-pulmonary TB patients was 1.1%, which was significantly different from 7.2% for 3332 patients with sputum smear-positive pulmonary TB (p < 0.001), as well as from 2.1% for 2139 patients with sputum smear-negative and bacillus-positive pulmonary TB (p < 0.05). The ICR differences were not significant between extra-pulmonary TB patients and 3,158 patients with bacteriologically negative pulmonary TB (1.2%). Of the 16 index cases with extra-pulmonary TB, the organs in which tuberculosis was found were the pleura in 13 patients, the bone in two, and the hilar nodes in one. The relationship between the 16 index cases and 18 secondary patients were husband-wife in 7 pairs, parent-child in 7 pairs, brother or sister in 2 pairs, and grandparent-grandchild in 2 pairs. The interval of the dates of registration for the index and secondary patients was within one year in 14 pairs or 77.8%.
Discussion: The index cases with extra-pulmonary TB can be considered as a good control in the epidemiological study on the ability of TB transmission in patients with pulmonary tuberculosis, so that they can form clusters by chance, or false positive clusters.
Conclusion: Our findings suggest that patients with extrapulmonary TB have no ability of TB transmission, nor do patients with bacteriologically negative pulmonary TB.