Evaluation of the pacific biotech CARDS STREP A test for detecting group A streptococci from cases of pharyngitis

Rapid antigen detection test for group A streptococcus in children with pharyngitis

BACKGROUND

Group A streptococcus (GAS) accounts for 20% to 40% of cases of pharyngitis in children; the remaining cases are caused by viruses. Compared with throat culture, rapid antigen detection tests (RADTs) offer diagnosis at the point of care (within five to 10 minutes).

OBJECTIVES

To determine the diagnostic accuracy of RADTs for diagnosing GAS in children with pharyngitis. To assess the relative diagnostic accuracy of the two major types of RADTs (enzyme immunoassays (EIA) and optical immunoassays (OIA)) by indirect and direct comparison.

SEARCH METHODS

We searched CENTRAL, MEDLINE, EMBASE, Web of Science, CDSR, DARE, MEDION and TRIP (January 1980 to July 2015). We also conducted related citations tracking via PubMed, handsearched reference lists of included studies and relevant review articles, and screened all articles citing included studies via Google Scholar.

SELECTION CRITERIA

We included studies that compared RADT for GAS pharyngitis with throat culture on a blood agar plate in a microbiology laboratory in children seen in ambulatory care.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened titles and abstracts for relevance, assessed full texts for inclusion, and carried out data extraction and quality assessment using the QUADAS-2 tool. We used bivariate meta-analysis to estimate summary sensitivity and specificity, and to investigate heterogeneity across studies. We compared the accuracy of EIA and OIA tests using indirect and direct evidence.

MAIN RESULTS

We included 98 unique studies in the review (116 test evaluations; 101,121 participants). The overall methodological quality of included studies was poor, mainly because many studies were at high risk of bias regarding patient selection and the reference standard used (in 73% and 43% of test evaluations, respectively). In studies in which all participants underwent both RADT and throat culture (105 test evaluations; 58,244 participants; median prevalence of participants with GAS was 29.5%), RADT had a summary sensitivity of 85.6%; 95% confidence interval (CI) 83.3 to 87.6 and a summary specificity of 95.4%; 95% CI 94.5 to 96.2. There was substantial heterogeneity in sensitivity across studies; specificity was more stable. There was no evidence of a trade-off between sensitivity and specificity. Heterogeneity in accuracy was not explained by study-level characteristics such as whether an enrichment broth was used before plating, mean age and clinical severity of participants, and GAS prevalence. The sensitivity of EIA and OIA tests was comparable (summary sensitivity 85.4% versus 86.2%). Sensitivity analyses showed that summary estimates of sensitivity and specificity were stable in low risk of bias studies.

AUTHORS' CONCLUSIONS

In a population of 1000 children with a GAS prevalence of 30%, 43 patients with GAS will be missed. Whether or not RADT can be used as a stand-alone test to rule out GAS will depend mainly on the epidemiological context. The sensitivity of EIA and OIA tests seems comparable. RADT specificity is sufficiently high to ensure against unnecessary use of antibiotics. Based on these results, we would expect that amongst 100 children with strep throat, 86 would be correctly detected with the rapid test while 14 would be missed and not receive antibiotic treatment.

Evaluation of the patient with sore throat, earache, and sinusitis: an evidence based approach

Sore throat, earache, and sinusitis are common presenting complaints in the emergency department, and all fall within the top ten in the United States. These complaints usually have a benign course but rarely can be a symptom of a serious disease process. This article provides an evidence-based review of the literature regarding the diagnosis of pharyngitis, otitis media, and sinusitis.

Evaluation of a new immunologic test kit for rapid detection of group A streptococci, the Abbott Testpack Strep A plus

We compared the Testpack Strep A plus (TPSAP) enzyme-linked immunosorbent assay test for group A beta-hemolytic streptococcal (GAS) antigen rapid detection with blood agar culture in 454 pediatric patients with clinical pharyngitis. Of the 454 patients, 118 (25.9%) had positive oropharyngeal cultures for GAS. TPSAP sensitivity was 89.9% (106 of 118) and specificity was 95.8% (322 of 336). We conclude that the TPSAP is specific enough to indicate treatment for a patient with a positive test but that a negative test should be confirmed by culture.

Novel, rapid optical immunoassay technique for detection of group A streptococci from pharyngeal specimens: comparison with standard culture methods

A novel immunoassay system based on the changes in the reflection of light, termed an optical immunoassay (OIA), was utilized to directly detect group A streptococcal (GAS) carbohydrate antigen from clinical specimens. In two studies, a total of 1,275 throat swabs were tested for the presence of this antigen with the Strep A OIA rapid detection system and the results were compared with those of standard culture methods. In both studies, the Strep A OIA yielded more positive results than plating of the throat swab onto a selective agar, Trypticase soy agar containing sheep blood, or an enriched broth. In one study, the sensitivity and specificity of Strep A OIA compared with those of the broth-enriched culture were 97.4 and 95.6%, respectively. In a second study a sensitivity of 98.9% and a specificity of 98.6% were achieved. It was also shown that the carbohydrate antigen could be detected in the absence of viable GAS organisms. The Strep A OIA is an easily interpretable method and was shown to be more sensitive than routine culture methods for detecting GAS infections directly from throat swabs.

Rapid antibody capture assay for detection of group-A streptococci using monoclonal antibody and colloidal gold-monospecific polyvalent antibody conjugate

A rapid one step, sensitive and specific antibody capture assay for detection of group-A streptococci from the throat swabs of children is described. Monoclonal antibody either MA-106 or MA-107 specific for group-A streptococci polysaccharide (APS) was used as the capture antibody on nitrocellulose paper and rabbit monospecific polyvalent antibody conjugated with colloidal gold to detect the presence of antigen. The lower detection limit of this assay is 15.6ng APS/ml. The assay is specific for APS and failed to recognize polysaccharides obtained from group-B,-C,-G streptococci as well as Staphylococcus aureus. Antigen extracted from throat swabs of children who were positive for beta-hemolytic plaques (other than group-A streptococci) as seen on blood agar culture gave negative readings, thereby confirming the specificity of the assay for APS.

Streptococcal throat infection: calculation of test standards and a comparison between an antigen detection test and culture

The standard minimum sensitivity (94%) and minimum specificity (89%) of a group A streptococcus (GAS) test were calculated, assuming that no more than 10% false positive and no more than 2% false negative test results should be allowed. The clinical judgement of the need for immediate antibiotic treatment in tonsillitis/pharyngitis was an unreliable indicator of a GAS aetiology, 20-29% of the results being false positive and 2-10% false negative. The rapid antigen detection test Tandem Icon Strep A was not sensitive enough to be used as a single test, though it was specific enough. The sensitivity of culture almost reached the standard demand. Two combinations of rapid test and culture (sequence testing) were superior to the rapid test, but were not significantly better than culture.

Evaluation of the modified Visuwell Strep-A enzyme immunoassay for detection of group-A Streptococcus from throat swabs

The modified Visuwell Strep-A enzyme immunoassay (EIA) was compared with culture for detection of group-A Streptococcus from throat swabs. Throat swabs in modified Stuarts medium obtained after culture at two institutions were tested in Visuwell. Cumulative results were n = 417, sensitivity 87.8%, specificity 89.9% predictive value positive (PVP) 67.9%, predictive value negative (PVN) 96.8%, and accuracy 89.5%. At another site, swabs were delivered to the laboratory without transport medium, cultured, and subsequently tested by Visuwell (n = 202, sensitivity 79.6%, specificity 84.5%, PVP 65.2%, PVN 91.9%, accuracy 83.2%). When 1+ culture-positive specimens were considered negative, the sensitivity and PVN increased from 79.6% to 90.2% and 91.9% to 97.1% respectively. Overall performance of the modified Visuwell was comparable with that of the initial assay for throat swabs transported with or without modified Stuarts medium. Cross reaction with organisms other than group-A Streptococcus normally found in the oropharynx was negligible in Visuwell and the limit of detection of group-A Streptococcus was 5 x 10(4) colony-forming units.