Sex differences in the epidemiology of tuberculosis in San Francisco

SETTING: Worldwide differences in sex-specific tuberculosis case rates rema in fundamentally unexplained. OBJECTIVE: To explore various factors that may explain sex differences in t uberculosis 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 IS611 0 data was used to study sex differences in the incidence of disease for re cently 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-specifi c rates after the age of 14 and the highest male:female ratios were seen in the US-born, white, and blade 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 o f tuberculosis, ratios were also above unity after adolescence, but the eff ect was less pronounced. CONCLUSION: The ongoing transmission of tuberculosis in the US-born populat ion is one of the factors that explains the difference in sex-specific rate s of disease in San Francisco. Observed differences in tuberculosis rates b etween the sexes may be due to a difference in transmission dynamics rather than diagnosis or reporting biases.