Sexually transmitted diseases (STD) are defined as a group of communica- ble diseases which have in common that they are transmitted predominantly by sexual contact. The number of agents now known to be sexually trans- mitted include some 20 pathogens. Some of these agents (such as Chlamydia trachomatis, herpes simplex virus, human papilloma virus, hepatitis Br virus, human immunodeficiency virus) tend to replace the classical "vene- real diseases" both in importance and frequency as these agents are often more difficult to detect, treat, and control.

Sexually transmitted diseases are a major public health problem in most African countries on account of their frequency, their associated morbidity and mortality, their impact on maternal and infant health, as well as their economic costs in terms of health expenditure and lost productivity, and, last but not least, because of their social consequences. Recent epidemio- logical studies using sophisticated diagnostic technologies greatly extend our knowledge on the true spectrum of complications and sequelae asso- ciated with these infections.

Nongonococcal urethritis - caused to 40% by Chlamydia trachomatis - and gonococcal infections are together the most frequent sexually transmitted diseases. The increasing importance of chlamydial infections, in contrast to a gradual decrease of gonococcal infections, is related to thefact that these infections frequently cause asymptomatic or mild disease and do not motivate patients to seek medical care, resulting in an extended period of infectivity and high risk of developing complications. Untreated gonorrhoea and chlamydial infections are the most common causes of epididymitis in males under the age of 35 years and may lead to decreased fertility. In some parts of sub-saharan Africa where urethritis often goes untreated, epididymitis is the leading course of male infertility. Also urethral strictures still from a large part of urogenital practice in some African countries.