Use of a High-Sensitivity Rapid Strep Test Without Culture Confirmation of Negative Results

Acute pharyngitis is one of the most common ill-nesses in children and adults in the United States and one of the leading reasons for outpatient office visits.¹ In both children and adults, the majority of cases are of viral etiology. Only 5% to 30% of pharyngitis patients are infected with group A b-hemolytic streptococci (GABHS), with the higher incidence being more common among pediatric populations during the winter months.^2-4 Accurate diagnosis of infections due to GABHS is important, since antibiotic therapy has been shown to shorten the clinical course,^5,6 reduce the rate of transmission,⁷ and prevent suppurative and nonsuppurative complications, such as peritonsillar abscess and acute rheumatic fever.^8,9

Although many clinical scoring systems have been developed to help with the diagnosis of pharyngitis due to GABHS, physicians vary greatly in their ability to diagnose streptococcal infections accurately on clinical grounds alone.^2,4,10,11 Because of this variability, both the American Academy of Pediatrics and the American Heart Association have recommended the use of either throat culture or an antigen detection test with culture confirmation of all negative results as the standard of care.^12,13 The rationale for culture confirmation is based on the historically low sensitivity of most antigen detection tests compared with blood agar plate (BAP) cultures.^14-16 Because of this low sensitivity, it has been feared that falsely negative results might lead to an increase in otherwise preventable suppurative and nonsuppurative complications. However, with the current commercial availability of a rapid antigen test with sensitivity equivalent or superior to BAP culture,^17,18 these recommendations have been challenged.^18,19

To date, there have been no clinical outcomes studies on the use of streptococcal antigen tests without culture confirmation. In our study, we examined the effect of a systemwide change in the management of pharyngitis on subsequent complication rates at the Lahey Clinic. Before April 1996, BAP culture was the sole test available for the diagnosis of streptococcal pharyngitis at the clinic. After demonstrating both high sensitivity and a beneficial effect on therapeutic decisions and appropriate antibiotic use associated with the use of a high-sensitivity antigen test¹⁹ (STREP A OIA, BioStar, Inc, Boulder, Colorado), the Department of Laboratory Medicine suggested that primary care physicians at the Lahey Clinic begin using this test without culture confirmation as the preferred method of diagnosis in April 1996. Although primary care physicians would still be able to order BAP cultures either alone or in combination with the high-sensitivity antigen test, reflexive culture confirmation of all negative antigen test results would no longer be performed. In this study, we compared the number of suppurative and nonsuppurative complications during 2 time periods: when throat culture was performed almost exclusively (period 1) and when the high-sensitivity antigen test without culture confirmation was the test performed in the majority of cases (period 2).

Methods

Setting

The Lahey Clinic is an integrated delivery system based in Burlington, Massachusetts, with a major satellite medical center in Peabody, Massachusetts. At these 2 locations, the Lahey Clinic medical staff includes more than 300 physicians in all disciplines. Primary, specialty, and hospital care are delivered to more than 650,000 patients each year at these 2 locations. Patients treated at the other 35 satellite offices of the clinic were not included in this study.