• Get men and women to treatment who have unrecognized or asymptomatic STDs;
• Avoid sequelae in patients and, for pregnant women, in the fetus and newborn;
• Identify STDs in homosexuals, who may be reluctant to seek care and reveal their sexual orientation;
• Identify people who may not have STDs but are at risk and need counseling; and
• Provide information about the prevalence of STDs in clinic populations.

How many infected people can screening programs identify? The answer depends on the prevalence of STDs in the population. The Mozambique project, for example, treated almost 39,000 people with STDs and their sexual partners. There are approximately 50,000 births in the province every year, and the prevalence of syphilis among pregnant women is 18% when measured by the RPR test (21). Thus screening all pregnant women for syphilis by RPR might detect about 9,000 cases. If one-quarter of the women's partners also were treated, the total number brought to treatment by screening would be 11,250. If syphilis prevalence were lower, of course, screening would bring fewer infected people to treatment. Because the RPR test is not 100% sensitive or specific, however, some of the women with syphilis would not be detected, and some who tested positive would not be infected. In the US a nationwide gonorrhea screening program begun in 1972 discovered about one-third of the gonorrhea cases reported between 1973 and 1975 and lowered the incidence of gonorrhea by about 20% (330).

Without tests, or if testing is too expensive, providers may use the syndromic approach to screen for STDs. Such screening may be used in place of laboratory tests or to identify people who need testing. Syndromic diagnosis can be based on patients' description of symptoms, a sexual history, and/or a gynecological exam. For example, in Tanzania syndromic screening of women attending an antenatal clinic based risk assessment on age, number of partners in the last year, reported vaginal discharge or itching, and vaginal discharge seen on examination. The assessment assigned one or two points to each risk factor, symptom, and sign. With a score of six points or more, the assessment was considered positive. Among 97 women, the risk assessment detected five STD cases. Screening based on the gynecological exam alone detected four cases. Screening based on symptoms alone detected three cases. In fact, laboratory testing found that 7 of the 97 women had chlamydia or gonorrhea. The risk assessment cost 50% less per case treated than screening based on the gynecological exam and symptoms (107).

Ideally, each program should check its risk assessment procedure in the same way—by comparison with lab test results. Risk assessments may work well in some populations but not in others. Two US studies of chlamydia screening found that a risk assessment identified 70% and 90% of family planning clients with chlamydia (2, 111). In contrast, another study found that a risk assessment missed three-quarters of infected women (316). Programs may need to adapt the risk assessment to improve its predictive value. For example, the score to indicate infection may be set higher or lower to hold down costs, on one hand, or to be sure of identifying as many cases as possible, on the other.