In the Journals

Culture confirms GAS in some with negative rapid test

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June 10, 2014

Reflexive culture for group A streptococcal pharyngitis is useful to confirm negative rapid antigen detection test results in adults and adolescents, according to a report in Clinical Infectious Diseases.

These findings are contrary to the current Infectious Diseases Society of America clinical practice guidelines for group A streptococcal (GAS) pharyngitis, according study researcher Ferric Fang, MD, who also said the IDSA guidelines conflict with clinical laboratory guidelines from the College of American Pathologists.

Ferric Fang, MD 

Ferric Fang

“Many clinicians rely on clinical guidelines to guide their practice,” Fang, professor of laboratory medicine and microbiology at the University of Washington, told Infectious Disease News. “We hope that our study will persuade clinicians to perform backup cultures in patients with moderate-to-severe symptoms of pharyngitis when the rapid tests are negative, despite the conflicting recommendations from the IDSA guidelines.”

Fang and colleagues conducted a retrospective analysis of 726 adolescent and adult patients who had negative rapid antigen detection tests but positive GAS throat cultures from 2000 to 2011. The researchers reviewed medical charts to determine the complication rates, symptoms, treatment and bacterial burden in these patients.

Among these patients, 67.6% had no cough, 51.3% had tender or swollen anterior cervical lymphadenopathy, 47% had tonsillar swelling or exudate, and 13.8% had fever. Fifty-five percent of the patients had modified Centor scores of 2 or more, and 77% of the cultures had a 2+ growth or more. Lastly, 29 patients had peritonsillar abscesses and two had acute rheumatic fever.

Overall, 499 patients (68.7%) were treated for acute bacterial pharyngitis and the culture results triggered the initiation of antibiotics in 217 (43.5%) of those.

“This issue illustrates the dilemma between wanting to help the individual patient by administering antibiotics and wanting to minimize the problem of antibiotic resistance in the community by withholding antibiotics,” Fang said. “One extreme is giving antibiotics to all patients with significant symptoms of sore throat, and the other extreme is not treating anyone or relying on an insensitive rapid test. Our study argues that an optimal balance between these extremes might be achieved by performing backup throat culture in patients with moderate-to-severe symptoms and negative rapid tests.”

In the United States, an estimated 250,000 patients with strep throat may be deprived of treatment each year if cultures are not performed, Fang said, and he hopes that the IDSA pharyngitis guidelines will be re-evaluated and revised based on this study.

As throat cultures can reveal other pathogens that cause pharyngitis, he said an optimal approach to detecting and treating these organisms should be studied. – by Emily Shafer

Disclosure: Fang reports no relevant financial disclosures.

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