Background: The impact of demographic, clinical, and bacterial factors on new infection by Euro-American lineage Mycobacterium tuberculosis among contacts of patients with tuberculosis (TB) has not been evaluated.
Objective: To describe the risk factors for new infection by Euro-American M. tuberculosis sublineages in San Francisco, California.
Design: We included contacts of patients with TB due to Euro-American M. tuberculosis. Sublineages were determined by large-sequence polymorphisms. We used tuberculin skin testing or QuantiFERON®-TB Gold In-Tube to identify contacts with new infection. Regression models with generalized estimating equations were used to determine the risk factors for new infection.
Results: We included 1488 contacts from 134 patients with TB. There were 79 (5.3%) contacts with new infection. In adjusted analyses, contacts of patients with TB due to region of difference 219 M. tuberculosis sublineage were less likely to have new infection (OR 0.23, 95%CI 0.06-0.84) than those with other sublineages. Other risk factors for new infection were contacts exposed to more than one patient with TB, contacts exposed for 30 days, or contacts with a history of smoking or excessive alcohol consumption.
Conclusions: In addition to well-known exposure and clinical characteristics, bacterial characteristics independently contribute to the transmissibility of TB in San Francisco.