Context Sexually transmitted infections (STIs) are common in female sex workers
(FSWs) and may enhance susceptibility to infection with human immunodeficiency
virus type 1 (HIV-1).
Objective To examine regular antibiotic prophylaxis in FSWs as a strategy for
reducing the incidence of bacterial STIs and HIV-1.
Design, Setting, and Participants Randomized, double-blind, placebo-controlled trial conducted between
1998-2002 among FSWs in an urban slum area of Nairobi, Kenya. Of 890 FSWs
screened, 466 who were seronegative for HIV-1 infection were enrolled and
randomly assigned to receive azithromycin (n = 230) or placebo (n = 236).
Groups were well matched at baseline for sexual risk taking and STI rates.
Intervention Monthly oral administration of 1 g of azithromycin or identical placebo,
as directly observed therapy. All participants were provided with free condoms,
risk-reduction counseling, and STI case management.
Main Outcome Measures The primary study end point was incidence of HIV-1 infection. Secondary
end points were the incidence of STIs due to Neisseria gonorrhoeae, Chlamydia trachomatis, Trichomonas vaginalis, Treponema pallidum, and Haemophilus
ducreyi, as well as bacterial vaginosis. Analysis
of herpes simplex virus type 2 (HSV-2) infection was performed post hoc.
Results Seventy-three percent of participants (n = 341) were followed up for
2 or more years or until they reached an administrative trial end point. Incidence
of HIV-1 did not differ between treatment and placebo groups (4% [19 cases
per 473 person-years of follow-up] vs 3.2% [16 cases per 495 person-years
of follow-up] rate ratio [RR], 1.2; 95% CI, 0.6-2.5). Incident HIV-1 infection
was associated with preceding infection with N gonorrhoeae (rate ratio [RR], 4.9; 95% CI, 1.7-14.3) or C trachomatis (RR, 3.0; 95% CI, 1.1-8.9). There was a reduced incidence in the treatment
group of infection with N gonorrhoeae (RR, 0.46;
95% CI, 0.31-0.68), C trachomatis (RR, 0.38; 95%
CI, 0.26-0.57), and T vaginalis (RR, 0.56; 95% CI,
0.40-0.78). The seroprevalence of HSV-2 infection at enrollment was 72.7%,
and HSV-2 infection at baseline was independently associated with HIV-1 acquisition
(RR, 6.3; 95% CI, 1.5-27.1).
Conclusions Despite an association between bacterial STIs and acquisition of HIV-1
infection, the addition of monthly azithromycin prophylaxis to established
HIV-1 risk reduction strategies substantially reduced the incidence of STIs
but did not reduce the incidence of HIV-1. Prevalent HSV-2 infection may have
been an important cofactor in acquisition of HIV-1.