The epidemiology of gonorrhoea, chlamydial infection and syphilis in four African cities.

Objectives: To compare the epidemiology of gonorrhoea, chlamydial infection and syphilis in four cities in sub-Saharan Africa; two with a high prevalence of HIV infection (Kisumu, Kenya and Ndola, Zambia), and two with a relatively low HIV prevalence (Cotonou, Benin and Yaoundé, Cameroon).

Design: Cross-sectional study, using standardized methods, including a standardized questionnaire and standardized laboratory tests, in four cities in sub-Saharan Africa.

Methods: In each city, a random sample of about 2000 adults aged 15-49 years was taken. Consenting men and women were interviewed about their socio-demographic characteristics and their sexual behaviour, and were tested for HIV, syphilis, herpes simplex virus type 2 (HSV-2), gonorrhoea, chlamydial infection, and (women only) Trichomonas vaginalis infection. Risk factor analyses were carried out for chlamydial infection and syphilis seroreactivity.

Results: The prevalence of gonorrhoea ranged between 0% in men in Kisumu and 2.7% in women in Yaoundé. Men and women in Yaoundé had the highest prevalence of chlamydial infection (5.9 and 9.4%, respectively). In the other cities, the prevalence of chlamydial infection ranged between 1.3% in women in Cotonou and 4.5% in women in Kisumu. In Ndola, the prevalence of syphilis seroreactivity was over 10% in both men and women; it was around 6% in Yaoundé, 3-4% in Kisumu, and 1-2% in Cotonou. Chlamydial infection was associated with rate of partner change for both men and women, and with young age for women. At the population level, the prevalence of chlamydial infection correlated well with reported rates of partner change. Positive syphilis serology was associated with rate of partner change and with HSV-2 infection. The latter association could be due to biological interaction between syphilis and HSV-2 or to residual confounding by sexual behaviour. At the population level, there was no correlation between prevalence of syphilis seroreactivity and reported rates of partner change.

Conclusion: Differences in prevalence of chlamydial infection could be explained by differences in reported sexual behaviour, but the variations in prevalence of syphilis seroreactivity remained unexplained. More research is needed to better understand the epidemiology of sexually transmitted infections in Africa.