Rapid strep tests in the pediatric clinical setting

Abstract

I T IS FRIDAY afternoon in a busy elementary school-based clinic, 7-year-old Crystal is referred due to a temperature of 102~ is complaining of a sore throat, pain with swallowing, headache, and stomach ache. Her physical exam reveals tonsillopharyngeal erythema, and tender, enlarged cervical lymph nodes. Tonsils are 2+ with slight patchy exudate. Crystal's family does not have a phone and there is no identified emergency contact. It will take considerable school resources to locate her mother. A routine throat culture result would be available Monday, but there is difficulty contacting Crystal's mother to either start an antibiotic if the culture is positive, or stop the antibiotic, if the culture is negative. Pharyngitis is a common symptom seen in pediatric populations. The most frequent cause of bacterial pharyngitis is group A beta-hemolytic streptococci (GABHS). Although the cause of pharyngitis is often viral, it is important to make an accurate diagnosis because GABHS can have acute morbidity and can lead to serious complications such as peritonsillar abscess, cervical lymphadenitis, rheumatic fever, and glomerulonephritis (Committee on Infectious Diseases of the AAP, 1997). Antimicrobial therapy should start as soon as possible in order to improve the clinical course of the GABHS illness and reduce the risk of transmission of the organism to others (Gerber, 1989; Randolph, Gerber, DeMeo, et al., 1985). The gold standard for diagnosis of GABHS pharyngitis is a throat swab specimen on a sheep blood agar plate. It is a highly accurate and sensitive test (Gerber, 1989). However, the disadvantage is the delay in obtaining results, often 24 to 48 hours later. This makes it particularly difficult with situations like the case scenario presented. The rapid antigen detection tests offer quick results in identifying GABHS pharyngitis. In 1988 Congress passed the Clinical Laboratory Improvement Amendments (CLIA) which set standards to improve the quality of clinical laboratory testing (National Committee for Clinical Laboratory Standards, 1992). This has allowed clinics to provide sophisticated scientific tests, such as the rapid strep test, to screen and confirm diagnoses or observations made by health care providers. All clinics that perform laboratory testing on-site hold a certificate from their state health department which authorizes testing, such as a nonculture Group A rapid strep screen. The rapid strep test takes a few minutes to perform and is easily read. The screens are only for use in the qualitative detection of GABHS; the rapid strep test does not differentiate between asymptomatic carriers and those patients with GABHS infection. Most of the current rapid strep screens have an excellent specificity of 95% or greater as compared with blood agar plate cultures (Gerber, 1989). Therefore, it is very unusual to get a false-positive result. If the rapid strep screen indicates a positive result, then antibiotic treatment should be instituted, (Gerber, 1997). The accuracy of the rapid antigen detection tests rely on staff who are well-trained in the steps involved in the screening test and good quality control procedures. The first step in the procedure is to take the throat specimen using only the swabs provided in the test kit box. Using a tongue blade to hold the tongue down, the specimen should be taken directly from the back of the throat, being careful not to touch the teeth, cheeks, gums, or tongue when inserting or removing the swab. The throat should be swabbed, not gently touched, and the specimen should be obtained from both tonsils (or fossae) and the posterior pharyngeal wall. If exudate is present, those areas should be collected