An investigation of geographic clustering of repeat cases of gonorrhea and chlamydial infection in San Francisco, 1989-1993: evidence for core groups.

To determine whether there were core groups of transmitters of gonorrhea and chlamydial infection among 14- to 35-year-olds in San Francisco during 1989-1993, sociodemographic risk factors for repeat gonorrhea and chlamydial infection were examined. During those 5 years, 8613 cases of gonorrhea were reported among males and 3893 among females; the proportions with repeat infection were 17.0% and 19.0%, respectively. There were also 2465 reported cases of chlamydial infection among males and 6996 among females; the proportions with repeat infection were 8.6% and 15.1%, respectively. Multivariate analyses reveal that for males, city planning region 5 was an independent risk factor for both repeat gonorrhea (relative hazard [RH] = 1.22; 95% confidence interval [CI] = 1.05-1.43) and repeat chlamydial infection (RH = 1.78; 95% CI = 1.23-2.57). For females, city planning region 4 was an independent risk factor for repeat gonorrhea (RH = 1.50; 95% CI = 1.12-1.98), and there was no high-risk planning region for repeat chlamydial infection. In San Francisco, there appear to be male and female core transmitters for gonorrhea but there may not be core transmitters for chlamydial infection.