Most experts recommend no testing or treatment of children who present with pharyngitis as a part of an obvious viral illness. But what about the rest?
As I noted last month, the primary reason for antibiotic treatment of GABHS infection is to prevent rheumatic fever. Most authorities concede that GABHS need not be treated immediately to prevent this unusual complication. In theory, the only reason to identify GABHS infections at the initial medical visit is to afford the child earlier relief of symptoms. That's a nice theory. It is even backed by some evidence suggesting that the most cost-effective strategy for managing pharyngitis is to eliminate those with obvious viral illnesses, culture the rest, and treat only those with positive throat cultures.
Unfortunately, the emergency department is not a suburban pediatric private practice. Unlike those doctors whose patients are on the phone asking for results an hour after the throat swab was collected, we often deal with a high-risk population without access to primary care and sometimes without a phone. These patients are easily lost to follow-up. For emergency physicians, making a diagnosis at the initial visit is appealing, to say the least. This begs the question: What is the best way to make the diagnosis? If we've eliminated the strategy of culture and wait, then we are left with two options. We can make a presumptive diagnosis using clinical criteria alone and treat on that basis or we can use rapid diagnostic testing.
Many investigators have attempted to define the clinical criteria by which GABHS pharyngitis can be reliably identified, and it should be noted that these are not just clinical impressions. There is ample medical literature demonstrating that, left to our own devices, we physicians tend to diagnose patients with GABHS infections liberally and treat them with antibiotics. Instead these relatively strict criteria force the clinician to determine the presence or absence of signs and symptoms known to increase or decrease the patient's risk for GABHS infection. The best known criteria were developed by Centor et al. The four Centor criteria are the presence of fever, exudative pharyngitis, and tender anterior cervical lymph nodes and the absence of viral symptoms.
An adult with all four Centor criteria has roughly a 50 percent chance of having a positive throat culture. Although the Centor criteria are intended for use only in adults, McIsaac et al modified the Centor criteria for use in children by adding an extra point if the patient is under 15. Trials of their criteria have demonstrated that their rules work at least as well if not better than the Centor rules.
Other investigators have developed similar criteria. Attia demonstrated that children with a scarlatiniform rash are very likely to have positive throat cultures. Wald included season of the year in her scoring system because GABHS tends to occur primarily in the fall and winter. These rules help reduce the unnecessary use of antibiotics, but none is perfect. They tend to be more useful when identifying children who are good candidates for presumptive treatment than when excluding those who do not require antibiotics because some children with few of the criteria still have the infection.
Rapid Antigen Testing
Another method for identifying patients with GABHS infections while they are still in the emergency department is rapid antigen testing (RADTs). The RADTs currently used rely primarily on optical immune assay technology (OIA) and are highly specific. That is, a positive RADT can be used to treat the patient without confirmatory culture. The sensitivity of these tests is a matter of some debate, however. Some authors have found OIA RADTs to be nearly as sensitive as throat cultures (greater than 95%) while others have found them to have sensitivities in the 80% to 85% range.
Currently, most experts recommend that a negative RADT be confirmed with a culture in children under 15. Several allow an exception when the physician has compared RADTs with throat cultures in his own practice and determined them to have equivalent sensitivities. Virtually all recommendations acknowledge that the incidence of rheumatic fever is lower and its consequences less dire in adults. A negative RADT may be used to exclude GABHS infection in patients under 15.
Centor RM, et al. The diagnosis of strep throat in adults in the emergency room. Med Decis Making
Wald ER, et al. A streptococcal scorecard revisited. Pediatr Emerg Care
McIsaac WJ, et al. Empirical validation of guidelines for the management of pharyngitis in children and adults. JAMA
Attia MW, et al. Performance of a predictive model for streptococcal pharyngitis in children. Arch Pediatr Adolesc Med