Rapid diagnosis of streptococcal pharyngitis with enzyme immunoassay.
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Abstract:
From June 1988 to May 1989, 444 throat swab specimens were tested with an enzyme immunoassay kit for rapid diagnosis of group A streptococcal pharyngitis. The results were compared with those of throat culture method. The rapid test was positive in 37 of 42 culture-positive specimens and negative in 379 of 402 culture-negative specimens, thus yielding a total agreement of 93.7%, sensitivity 88.1%, specificity 94.7%, positive predictive value 61.7%, negative predictive value 98.7%. According to this practical application, we suggest that enzyme immunoassay test can be applied in outpatient clinics by busy pediatricians for rapid diagnosis of group A streptococcal pharyngitis.Keywords:
Throat culture
Throat
Outpatient clinic
Group A
Positive predicative value
Microbiological culture
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Throat
Throat culture
Group A
Streptococcus Pyogenes
Microbiological culture
Group B
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Background. In evaluations of sensitive rapid tests for group A streptococci such as the optical immunoassay (OIA), some samples are positive by the antigen test but negative by culture. A method is needed for resolving these discrepant results. Objective. To develop a PCR-based assay to detect group A streptococci and to use it to establish a reference standard for evaluating an OIA for group A streptococcal antigen. Methods. A PCR assay that detects a segment of the MF gene of Streptococcus pyogenes was developed for the detection of group A streptococci in throat swabs. Paired swabs were obtained from 200 children with symptomatic pharyngitis and used to perform OIA, agar culture, brothenhanced culture and PCR. As a reference standard any patient with group A streptococci detected by either culture or PCR was considered to be truly positive. Results. In comparison to agar and broth-enhanced culture procedures, OIA had sensitivities of 82 and 80% and specificities of 87 and 89%, respectively. Eight (44%) of 18 samples that were positive by OIA but negative by culture were positive for group A streptococci by PCR. Compared with the reference standard, sensitivities were OIA 76%, agar culture 79%, broth-enhanced culture 86% and PCR 96%. The specificity of OIA was 92%. Conclusions. PCR can be used to establish a reference standard for evaluating rapid tests for group A streptococci. With this reference standard OIA was nearly as sensitive as but less specific than agar culture for detection of group A streptococci. Maximum detection requires use of both tests.
Streptococcus Pyogenes
Group A
Group B
Throat culture
Microbiological culture
Throat
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Throat culture
Streptococcus Pyogenes
Group A
Throat
Microbiological culture
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Citations (24)
From June 1988 to May 1989, 444 throat swab specimens were tested with an enzyme immunoassay kit for rapid diagnosis of group A streptococcal pharyngitis. The results were compared with those of throat culture method. The rapid test was positive in 37 of 42 culture-positive specimens and negative in 379 of 402 culture-negative specimens, thus yielding a total agreement of 93.7%, sensitivity 88.1%, specificity 94.7%, positive predictive value 61.7%, negative predictive value 98.7%. According to this practical application, we suggest that enzyme immunoassay test can be applied in outpatient clinics by busy pediatricians for rapid diagnosis of group A streptococcal pharyngitis.
Throat culture
Throat
Outpatient clinic
Group A
Positive predicative value
Microbiological culture
Cite
Citations (1)
The Culturette Brand® rapid latex agglutination test was compared with the throat culture for accuracy in detecting Group A beta-hemolytic streptococci (GABHS) on paired throat swabs from 1047 children with suspected streptococcal pharyngitis. In this comparison the rapid latex agglutination test had a sensitivity of 78%, a specificity of 88%, a positive predictive value of 52% and a negative predictive value of 96%. In 45 study patients from whom it was possible to obtain paired acute and convalescent sera, the latex agglutination test and the throat culture were compared against each other for detection of infection due to GABHS as evidenced by a 4-fold or greater titer rise of serum antistreptococcal antibodies. The latex agglutination test detected and failed to detect the same number of infections as the throat culture. Thus although a significant number of false positive latex agglutination tests occurred when compared to the throat culture, there is limited evidence in this study that the latex agglutination test is equal to the throat culture in detecting patients who have serologically confirmed infection due to GABHS.
Throat culture
Latex fixation test
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Agglutination (biology)
Streptococcus Pyogenes
Direct agglutination test
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Group A streptococcus (GAS) causes significant morbidity and mortality in New Zealand and is responsible for invasive disease and immune sequelae, including acute rheumatic fever (ARF). Early treatment of GAS pharyngitis reduces the risk of ARF. In settings with a high burden of GAS disease, a rapid GAS pharyngitis diagnostic test with a strong negative predictive value is needed to enable prompt and accurate treatment. This prospective study compares the Xpert Xpress Strep A molecular test (Cepheid) to throat culture and a second molecular method, the BioGX group A streptococcus-open system reagent (OSR) for BD Max for the diagnosis of GAS pharyngitis. Throat swabs were collected from the emergency department and wards of Middlemore Hospital, New Zealand. The BioGX group A streptococcus OSR for BD Max contributes to the composite gold standard of throat culture or both molecular methods positive. Basic demographic, clinical, and laboratory data were collected. Two hundred five out of two hundred fourteen swabs were suitable for analysis. Of those, 28/205 (13.7%) were GAS culture positive, 45/205 (22%) Xpert Xpress Strep A positive, and 38/205 (18.5%) BioGX positive. Compared to culture, the sensitivity, specificity, and positive and negative predictive values of the Xpert Xpress Strep A molecular test were 100%, 90.4%, 62.2%, and 100%, respectively. Compared to the composite gold standard, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 100%, 95.8%, 84.4%, and 100%, respectively. Seventeen samples were Xpert Xpress positive but culture negative; 6 of these 17 swabs represent true positives with evidence of recent GAS infection. Ten samples were culture negative but both Xpert Xpress and BioGX positive. The Xpert Xpress Strep A molecular test is highly sensitive with a strong negative predictive value and rapid turnaround time. It can be safely introduced as a first-line test for throat swabs in a high-incidence ARF population.
Throat culture
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Throat
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Sore throat
Positive predicative value
Microbiological culture
Streptococcus Pyogenes
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Comparison of TestPack Strep A test kit with culture technique for detection of group A streptococci
Results obtained with Abbott Laboratories TestPack Strep A (TPSA), a 7-min enzyme immunoassay method, were compared with culture results to measure the ability of this assay to detect group A streptococci directly from 365 throat swabs. Our study demonstrated a sensitivity of 90.0% and a specificity of 97.4% for TPSA compared with cultures incubated for 48 h. The positive and negative predictive values of this assay versus the culture method were 92.8 and 96.3%, respectively. If specimens that provided fewer than 10 colonies per plate of group A streptococci are eliminated from the data, the sensitivity is increased to 95.6%. Additionally, 10 group A and 40 non-group A streptococcal isolates were tested directly with TPSA for the ability to distinguish group A from non-group A streptococci. All 50 isolates were correctly identified (100% accuracy). TPSA is a rapid, accurate, and easy-to-interpret method for detection and confirmation of group A streptococcal antigen directly from throat swabs and pure culture isolates.
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Throat culture
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Streptococcus Pyogenes
Microbiological culture
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Throat culture
Throat
Group A
Streptococcus Pyogenes
Positive predicative value
False Negative Reactions
Group B
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Background: Group A β-hemolytic Streptococcal (GAS) pharyngitis is a common illness in children. Diagnosis and proper treatment of group A streptococcal sore throat is important particularly to prevent non-superlative sequel. Clinical findings continue to be used in differentiating streptococcal infection from viral sore throat. Objectives: The aim of this study was to evaluate the accuracy of clinical findings and rapid test in comparison with culture in the diagnosis of group A Streptococcal (GAS) pharyngitis. Patients and Methods: Ninety-four children between 3 to 16 years, who were referred to the pediatric clinic of Rasoul-e-Akram hospital with clinical findings of fever or sore throat were evaluated from October 2006 to May 2007. Clinical findings were recorded and swabs were taken for group A streptococcal cultures and streptococcal rapid antigen detection test. Analysis of statistical significance was performed using the chi-square method. The accuracy of clinical findings and rapid test was compared with the culture method as the gold standard, and sensitivity, specificity, positive predictive values, negative predictive value, positive likelihood ratio (LR+) and negative likelihood ratio (LR-) were calculated. Results: The culture was positive in 38 (40.4%) of the 94 evaluated children. The mean age of children was 8 ± 3.7 years. The presence of petechiae, exudate and Lymphadenopathy (LAP) was more likely in children with positive streptococcus culture and rapid test (P value < 0.05). Lymphadenopathy was known to feature the most sensitivity (100%), specificity (76.8%), and positive predictive value (74.5%), negative predictive value (100%) and positive likelihood ratio (LR) (4.3) among clinical findings. The results of rapid test showed sensitivity of 89.4%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 93.3% in comparison with culture as the gold standard. In general, the accuracy of rapid test was found higher than subjective clinical findings (P = 0.001). Conclusions: Although LAP had good performance in early diagnosis of GAS, a combination of clinical findings, including tonsillar exudates, petechiae with results of rapid antigen test or culture is necessary for clinician judgment. Throat culture is the gold standard test for detecting group A Streptococcal infection, but rapid test is a good replacement for culture.
Sore throat
Throat culture
Gold standard (test)
Group A
Throat
Positive predicative value
Streptococcus Pyogenes
Group B
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Throat culture
Streptococcus Pyogenes
Throat
Group A
Group B
Microbiological culture
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Citations (24)