Background: Predictors of chlamydia and gonorrhoea can be used to increase the cost-effectiveness and acceptability of screening programmes, and allow targeting of control strategies.
Method: All men attending an STD clinic in 1988-1990 were offered screening for chlamydia and gonorrhoea, and the test results correlated with a wide range of potential predictors using multiple logistic regression.
Results: Of 9622 attenders, 7992 (82.3%) were tested over a total of 10,110 episodes for chlamydia and 10,090 episodes for gonorrhoea, yielding 729 (7.2%) chlamydial and 123 (1.2%) gonococcal infections. Having urethral discharge and/or dysuria, being heterosexual, and STD contact, unmarried, uncircumcised, tattooed and not having had an STD previously were independently associated with chlamydial infection. Having urethral discharge and/or dysuria, being Aboriginal, an STD contact, homosexual, uncircumcised, tattooed and having sex outside the state in the past three months, no steady partner in the past three months and multiple partners in the past month were associated with urethral gonococcal infection. Selective screening criteria for gonorrhoea provided 90% of positives, eliminated the need for 58% of tests and resulted in an increased yield ratio of 2.2 whereas the corresponding outcomes for screening criteria for chlamydia were 93% 20% and 1.2 respectively.
Conclusions: The widespread influence of confounding on potential predictors for both gonorrhoea and chlamydia may provide misleading indicators of risk factors by univariate analysis. In the setting studied the benefits of selective screening for gonorrhoea in men would be substantial, whereas satisfactory criteria for selective screening for chlamydia could not be identified.