Diagnosis of Streptococcal Pharyngitis by Detection of Streptococcus pyogenes in Posterior Pharyngeal versus Oral Cavity Specimens

Abstract

Carbohydrate antigen detection, nucleic acid probe detection, and bacterial culture are commonly used to confirm group A streptococcus (GAS) pharyngitis. Compared to standard throat swab specimens, the sensitivities of these tests with mouth specimens are poor. When testing for GAS pharyngitis, the throat remains the optimum site for sampling.Streptococcus pyogenes (group A streptococcus [GAS]) causes approximately 15 to 30% of pediatric sore throats (1). Accurate diagnosis permits appropriate administration of antimicrobial therapy to prevent complications, hasten symptom resolution, and reduce the transmission of GAS in the community (7,12,13). Unfortunately, clinical evaluation and scoring systems cannot reliably identify patients with streptococcal pharyngitis, necessitating the utilization of laboratory tests (3, 6). While culture of GAS on sheep blood agar medium remains the gold standard for detection of GAS in throat swab specimens (2), newer and more rapid diagnostic tests, including direct carbohydrate antigen and nucleic acid probe detection, are now available.Current methods of GAS pharyngitis testing rely on swab specimens obtained from the posterior pharynx and tonsils. This convention is based on recommendations published by the Infectious Diseases Society of America (IDSA), which defines specimens obtained from these sites to be the only adequate samples to test for the presence of Streptococcus pyogenes (2). It should be noted, however, that these recommendations are based on two small studies performed more than 20 years ago that evaluated only 32 patients (4, 9). In this study, we investigate the use of newer techniques of rapid direct carbohydrate antigen and nucleic acid probe detection to identify GAS in samples obtained purposively from the oral cavities and posterior pharynges of pediatric patients with sore throats. This comparison is of practical significance because it is often difficult to obtain a well-collected posterior pharyngeal swab specimen from young children.This study was approved by the Institutional Review Board of Columbus Children's Hospital and conducted with informed consent between September 2004 and February 2005. Fiftythree patients presenting with a chief complaint of sore throat to the Children's Hospital emergency department were enrolled as study subjects. Subjects ranged from 3 to 18 years of age; the only exclusion criterion was prior tonsillectomy.Each subject underwent two swab collections with a doubleswab collection/transport system (COPAN Venturi Transystem; COPAN Diagnostics Inc., Corona, CA). The standard posterior pharyngeal (throat swab) collection technique involved vigorous swab sampling of the posterior pharynx and bilateral tonsillar tissue while avoiding contact with the tongue, buccal surfaces, and lips. The oral cavity (mouth swab) collection technique involved blind sampling of the subject's mouth, targeting the tongue and buccal mucosa. Each subject was asked to rate his/her pain with a validated age-appropriate pain scale after each swab col...

Molecular and Clinical Diagnosis of Group A Streptococcal Pharyngitis in Children

“…Optimal sampling of the posterior pharynx is imperative but is difficult in young children, and culture sensitivity can be as low as 20% with suboptimal sampling techniques (10). Discrepancies seen between culture and illumigene GAS assay results in this study are unlikely to be due to sampling variability, as the same pediatric nurse collected the two swabs from each patient simultaneously.…”

“…Detection and identification of GAS from pharyngeal swabs represent the current gold standard for the microbiological diagnosis of GAS pharyngitis, with reported sensitivities between 90 and 95% (10,11). Optimal sampling of the posterior pharynx is imperative but is difficult in young children, and culture sensitivity can be as low as 20% with suboptimal sampling techniques (10).…”

“…Although the sensitivity of cultures has been reported to be 90% to 95%, multiple variables can affect the yield, including specimen integrity, culture methods, and prior antibiotic use (10)(11)(12). In addition, culture can take up to 48 h, delaying appropriate antimicrobial treatment (13).…”

Rapid Diagnostic Tests for Group A Streptococcal Pharyngitis: A Meta-analysis

“…This included number and type of throat swabs used, as well as techniques used to obtain these throat swabs. 19,23,29,46 Methods of sample collection were not clearly reported in all studies and there is no way to control the quality of the swab samples. Studies included also differed in their settings and the clinical severity of included patients.…”

“…6,[17][18][19][20] Where a different RADT was tested in the same sample of patients, we included each sensitivity and specificity pair in the subgroup analysis for the respective RADT. [21][22][23][24][25] Where multiple sensitivity and specificity pairs were estimated from the same patients in a study, only 1 pair of sensitivity and specificity was included in our analysis. 22,23,[25][26][27][28][29][30][31][32][33][34] We selected the pairs that were the focus of primary analysis of the selected studies.…”