Sex differences in the epidemiology of tuberculosis in San Francisco.

SETTING Worldwide differences in sex-specific tuberculosis case rates remain fundamentally unexplained. OBJECTIVE To explore various factors that may explain sex differences in tuberculosis incidence rates for San Francisco from 1991-1996. DESIGN A retrospective epidemiologic analysis of sex-specific tuberculosis incidence rates in San Francisco from 1991-1996. Stratified analyses were performed on age at diagnosis, racial/ethnic group, human immunodeficiency virus (HIV) status, and place of birth. Molecular fingerprinting with IS6110 data was used to study sex differences in the incidence of disease for recently transmitted and reactivated cases of tuberculosis. RESULTS In the study period, the male to female incidence rate ratio was 2.1 (95% CI 1.9-2.3). Stratified analyses revealed differences in sex-specific rates after the age of 14 and the highest male:female ratios were seen in the US-born, white, and black populations. High ratios were also observed for cases with clustered fingerprints, similar to those observed for the US-born population. In sub-populations with predominantly reactivated cases of tuberculosis, ratios were also above unity after adolescence, but the effect was less pronounced. CONCLUSION The ongoing transmission of tuberculosis in the US-born population is one of the factors that explains the difference in sex-specific rates of disease in San Francisco. Observed differences in tuberculosis rates between the sexes may be due to a difference in transmission dynamics rather than diagnosis or reporting biases.