CHICAGO — A prediction rule that takes into account penile discharge, sexual contact history, age, and insurance status can help emergency physicians rule out potential chlamydia or gonorrhea infections.
“While the ability to predict the presence of infection was modest, the rule did better at predicting the absence of infection,” Dr. Roland Merchant said at a conference on STD prevention sponsored by the Centers for Disease Control and Prevention.
Dr. Merchant, an emergency physician at Rhode Island Hospital, Providence, created the rule using hospital records for 822 men who were tested for chlamydia and/or gonorrhea at the ED from 1998 to 2004. The patients' mean age was 28 years; 48% of patients were black, 15% were Hispanic, 26% were white, and 11% were from other ethnic groups. About half of the patients (53%) had no health insurance.
Of the 822 patients, 14% had chlamydia, 12% had gonorrhea, and 3% had both infections, for a total STD prevalence of 29%. However, because bacterial culture is the only certain method of diagnosis and cultures take time to return results, most patients received antibiotic therapy presumptively. Almost all of those patients with infections did receive antibiotics (96%)—but so did 89% of those patients without infections.
“We need methods of limiting antibiotic usage to when it is indicated to avoid antibiotic overusage, reduce antibiotic resistance and costs, and avoid adverse reactions,” Dr. Merchant said.
To create the prediction rule, Dr. Merchant examined patient characteristics most strongly associated with infection. Most of the men (76%) had symptoms of a sexually transmitted infection that brought them to the ED. The most common was a combination of penile discharge and dysuria (45%). A total of 22% had dysuria alone, 17% had discharge alone, 2% had pain, 2% had lesions, and 11% had no symptoms at all. The rest had other symptoms.
Dr. Merchant concluded that penile discharge, sexual contact with a person with a known STD, age, and no insurance most strongly correlated with infection. Having at least three of these risk factors increased the odds of having chlamydia and/or gonorrhea by five times over having no risk factors.
The risk factors were much more accurate in predicting the absence of infection. Patients with no risk factors were 17 times less likely than were patients with at least two risk factors to have a chlamydia/gonorrhea infection. Those whose only risk factors were age younger than 24 years and/or no insurance were seven times less likely to be infected. Patients with only penile discharge or contact with someone with an STD were two times less likely, said Dr. Merchant, who made no financial disclosures.