Background:
Sexually transmitted infection (STI) screening in jails provides access to persons at high risk for STIs who might not be screened elsewhere. San Francisco has performed STI screening and treatment at the San Francisco County Jail since fall 1996.

Objective:
Determine STI trends at two neighborhood clinics serving populations with different incarceration rates.

Method:
Positivity rates of gonorrhea (GC) and chlamydia (CT) during the period 1997–2004 were compared at two neighborhood clinics: Clinic S, serving an area with high incarceration rates and Clinic O, serving an area with low incarceration rates.

Result:
A total of 31,375 men aged 18–30 years and 11,738 women aged 18–35 years underwent STI testing and treatment in jail. Blacks accounted for 48% of persons screened. On the basis of census data, 32% (n=1,324) of the neighborhood population in these age groups served by Clinic S had at least one screening test performed in jail, compared with 0.8% (n=53) of the neighborhood population served by Clinic O. Among females aged 15–25 years screened at Clinic S, the positivity rate for CT declined from 15.8% (89/564) in 1997–1999 to 8.1% (52/641) in 2002–2004 (Χ²=13.5, p<0.001) compared with a change from 3.3% (9/274) to 3.1% (5/161) (Χ²=0.01, p=0.9) at Clinic O for these time periods. GC positivity declined from 4.0% (25/626) to 2.5% (17/675) (Χ²=2.1, p=0.2) at Clinic S compared with continued low prevalence (range: 0%–0.8%) at Clinic O.

Conclusion:
In San Francisco, a 48% decrease in CT positivity and a 38% decrease in GC positivity occurred at a neighborhood clinic serving a population with a high incarceration rate.

Implications:
STI screening and treatment in corrections facilities can contribute substantially to community STI control programs.