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PEDIATRICS Vol. 111 No. 6 June 2003, pp. e666-e670

ELECTRONIC ARTICLE

Evaluating the American Academy of Pediatrics Diagnostic Standard for Streptococcus pyogenes Pharyngitis: Backup Culture Versus Repeat Rapid Antigen Testing

Karen E. Gieseker, PhD^*,, Martha H. Roe, SM (ASCP), Todd MacKenzie, PhD^# and James K. Todd, MD^*,,,||,¶

^* Departments of Epidemiology
Pathology, Children’s Hospital
Departments of Preventive Medicine
^|| Microbiology
^¶ Pediatrics, University of Colorado Health Sciences Center, Denver, Colorado
^# Department of Medicine, Dartmouth Medical School, Hanover, New Hampshire

Objective. The American Academy of Pediatrics recommends that all negative rapid diagnostic tests for Streptococcus pyogenes pharyngitis be backed up by culture, which creates a dilemma for clinicians who must make treatment decisions without complete diagnostic information at the time of visit. The use of a follow-up serial rapid antigen test instead of a follow-up culture would provide a more timely result.

Methods. Two swabs were collected from children who were suspected of having S pyogenes pharyngitis. Each swab was used for a culture and an OSOM Ultra Strep A Test rapid antigen test. The gold standard of comparison was defined as the identification of S pyogenes on either of the 2 culture plates. Three diagnostic strategies were evaluated: a single rapid antigen test, a rapid antigen test with follow-up rapid antigen test (rapid-rapid), and a rapid antigen test with follow-up culture (rapid-culture).

Results. A total of 210 (23.7%) of 887 throat cultures with matched data were identified with S pyogenes. A single rapid antigen test had a sensitivity of 87.6% (95% confidence interval [CI]: 83.2%–92.1%), the sensitivity of the rapid-rapid follow-up was 91.4% (95% CI: 87.6%–95.2%), and the sensitivity of the rapid-culture follow-up was 95.7% (95% CI: 93.0%–98.5%), which was significantly higher than the others. As shown in Fig 1, when these test strategies were evaluated on a subgroup with clinical symptoms commonly associated with S pyogenes pharyngitis, the sensitivities all increased and were no longer significantly different. None of the strategies reliably exceeded a 95% sensitivity threshold.

View larger version (16K): [in this window] [in a new window]   Fig 1. Sensitivity and 95% CI of throat culture diagnostic strategies. Asterisk indicates subgroup analysis of children with strong clinical criteria for S pyogenes pharyngitis.

 
Conclusions. The American Academy of Pediatrics strategy for S pyogenes detection in children with pharyngitis, requiring a backup culture for those with negative antigen tests, was not exceeded by any other test strategy; however, a rapid-rapid diagnostic strategy may approximate it with the use of judicious clinical selection of patients.

Key Words: group A Streptococcus • Streptococcus pyogenes • pharyngitis • rapid • antigen test • diagnosis • throat culture

Abbreviations: CLIA, Clinical Laboratory Improvement Act • AAP, American Academy of Pediatrics • CI, confidence interval • OIA, optical immunoassay

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Received for publication Oct 30, 2002; Accepted Feb 19, 2003.

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