[Influence of aging on tuberculosis infection--an epidemiological study of 1,141 smear-positive TB patients].

Objectives: To elucidate the influences of aging on the tuberculosis infection.
Subjects and Methods: The subjects of this retrospective study were 1,141 smear positive pulmonary tuberculosis (TB) patients registered in Aichi prefecture between 1989 and 2003. All registration files were reviewed to identify epidemiological links of patients. When linked patients with an interval of the dates of registration of less than 10 years were found, the earliest case was considered as the source case, and the other patients were regarded as secondary cases. An epidemic source rate (ESR) for a category of patients (e.g., age-group, etc.) was defined as following; ESR= NS/NA X 100, where NA: Number of smear-positive pulmonary TB patients in a category A, and NS: Number of source cases in category A.
Results: A total of 70 source cases were identifed and the ESR was 6.1%. The ESRs for different age-groups were; 14.3 % for 10-19 years of age (NA = 14), 13.5% for 20-29 years (NA = 74), 14.6% for 30-39 years (NA = 48), 15.0% for 40-49 years (NA = 107), 6.9% for 50-59 years (NA = 145), 3.5% for 60-69 years (NA = 227), 3.8% for 70-79 years (NA = 293), 2.8% for 80-89 years (NA = 212), and 0% for 90-99 years (NA = 21). The ESR were significantly different between those aged 40 to 49 years and those aged 50 to 59 (p<0.05). The ESR was significantly different between those aged 59 years and younger and those aged 60 years or older (11.6% vs 3.3%, p<0.001). The ESR was significantly different between those patients with cavitary lesion and those with noncavitary lesion in the younger groups (14.3% vs 5.2%, p<0.01), as well as in the elder age-groups (4.8% vs 1.7%, p<0.01). The rate in the younger groups was 6.3% for those with lower smear-positivity (Gaffky 1 to 4), compared with 15.3% for those with intermediate smear-positivitiy (Gaffky 5 to 8), and 32.4% for those with higher smear-positivity (Gaffky 9 and 10) (with p<0.01, p<0.05 respectively), while the rates were 3.1%, 3.9%, and 3.4%, respectively in the older groups.
Conclusion: These findings suggest that the infectivity is significantly lower in older groups.