Background:
Antibiotic resistance, adverse reactions, and costs concerns are driving methods to reduce antibiotic overusage.

Objective:
We created a clinical prediction rule for chlamydia and/or gonorrhea infections among adult male emergency department (ED) patients to help determine when empiric treatment should be initiated or withheld, pending the results of testing.

Method:
Retrospective study of adult male patients at a US ED tested for a possible chlamydia and/or gonorrhea infection from January 1998-December 2004. Statistical models were constructed to create a decision rule to predict either the presence or the absence of a laboratory-confirmed chlamydia and/or gonorrhea infection based upon patient demographic and presenting illness characteristics. Likelihood ratios (LRs) with 95% CIs were calculated. The decision rule was internally validated.

Result:
Among 822 patients tested, 29.2% had a chlamydia, gonorrhea, or both infections; 13.8% were infected with chlamydia alone, 12.1% were infected with gonorrhea alone, and 3.3% were infected with both. The following factors were identified as predictors of a laboratory-confirmed infection for the prediction rule: age °Ü 24 years, penile discharge, sexual contact with someone known to have chlamydia and/or gonorrhea, and not having health care insurance. The likelihood of an infection for patients with three or more risk factors was LR 2.70 (1.92-2.79), while the likelihood of no infection for no risk factors was LR 15.6 (3.12-78.30).

Conclusion:
Although the prediction rule developed through this study requires prospective, external validation, it appears that using a combination of risk factors revealed through the clinical encounter in the ED can modestly assist ED clinicians in predicting which patients are more likely to have or not have a chlamydia and/or gonorrhea infection

Implications:
The prediction rule could be used to help decide which patients should receive empiric treatment in the ED or when it could be deferred.