Comparison of TestPack Strep A test kit with culture technique for detection of group A streptococci
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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.Keywords:
Group A
Throat
Throat culture
Group B
Streptococcus Pyogenes
Microbiological culture
β-hemolytic streptococci, particularly members of Strebtococcus bvogenes, are important pathogens which cause various acute infections and post-streptococcal diseases. It is not uncommon that organisms of S. pyogenes are isolated from the throat of apparently healthy children. Therefore, the etiologic significance of a small number of S. pyogenes detected from children with symptoms of upper respiratory infections has not been determined yet. Thus there have been few laboratories which use a selective enrichment broth for detection of S. pyogenes.We made a clinical evaluation on the employment of a selective enrichment broth (SEB, Nissui Seiyaku) in detecting S. pyogenes from throat specimens of children, who visited the outpatient clinic at our hospital. It was observed that even a small number of S. pyogenes only detectable by employment of the SEB showed an etiologic relationship with the disease. The results indicated the usefulness of the SEB for culturing throat specimens from the children.
Streptococcus Pyogenes
Throat
Throat culture
Outpatient clinic
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Rapid streptococcal tests (RSTs) for streptococcal pharyngitis have made diagnosis at once simpler and more complicated. The American Academy of Pediatrics recommends that all RSTs be confirmed by a follow up throat culture unless local validation has proved the RST to be equally sensitive.To evaluate (a) RST as a single diagnostic tool, compared with RST with or without throat culture; (b) clinical diagnosis and the relative contribution of different symptoms.The study included 213 patients with clinical signs of pharyngitis. Throat swabs were analysed using Quickvue+ Strep A Test; negative RSTs were backed up by throat culture. Thirteen clinical features commonly associated with strep throat were analysed using backward stepwise logistic regression.Positive results (RST or throat culture) were obtained in 33 patients; RST correctly identified 21. Eleven samples were false negative on RST. At a strep throat prevalence of 15.9%, sensitivity of RST was 65.6% (95% CI 46.8% to 81.4%) and specificity 99.4% (96.7% to 99.9%). Sensitivity of clinical diagnosis alone was 57% (34% to 78%) and specificity 71% (61% to 80%). Clinically, only history of sore throat, rash, and pyrexia contributed to the diagnosis of strep throat (p<0.05).The high specificity of RST facilitates early diagnosis of strep throat. However, the low sensitivity of RST does not support its use as a single diagnostic tool. The sensitivity in the present study is markedly different from that reported by the manufacturer. Clinical examination is of limited value in the diagnosis of strep throat. It is important to audit the performance of new diagnostic tests, previously validated in different settings.
Throat
Throat culture
Sore throat
Clinical Diagnosis
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Despite its imperfections, the throat culture remains the "gold standard" against which all rapid streptococcal antigen detection tests are compared. Using triple throat swabs, the accuracy of a rapid latex agglutination (LA) test and back up throat culture was determined and compared with a simultaneously obtained additional throat culture in children with suspected streptococcal pharyngitis. Although there was a 95 percent concordancy between throat cultures, the sensitivity of the throat culture was only 87 percent. Despite the LA test's lower sensitivity (78 percent), in this clinical population with a relatively low prevalence of positive throat cultures (19 percent), the predictive value of a negative LA test was only slightly lower than that of the throat culture (94-95 percent vs. 97 percent). Backup throat cultures are commonly recommended for patients with initially negative LA test results, but 10 percent of the patients with group A beta-hemolytic streptococci-positive throat cultures would have been undetected using this approach.
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Throat culture
Gold standard (test)
Latex fixation test
Microbiological culture
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A co-agglutination test (Phadirect Strep A) for rapid detection of group A streptococci in throat swabs was compared with conventional throat culture in 264 patients with pharyngotonsillitis and fever. The test was easy to perform and proved to have a satisfactory sensitivity and specificity. The predictive value of a positive test will be high also when the prevalence of streptococcal disease is low.
Throat
Throat culture
Latex fixation test
Group A
Microbiological culture
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An attempt was made to establish a relationship between the presence of hoarseness and palatal petechiae and the results of throat cultures performed on children with acute throat infections. A total of 1,307 throat cultures were performed and the results were compared to the presence or absence of these two factors. It is concluded that, if a physician uses either of these two clinical "clues" to distinguish between streptococcal and non-streptococcal throat infections, he will be wrong one quarter of the time. The use of inexpensive office techniques for throat cultures is encouraged.
Throat
Throat culture
STREPTOCOCCAL INFECTIONS
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Throat
Throat culture
Subclinical infection
Group A
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Throat
Streptococcus Pyogenes
STREPTOCOCCAL INFECTIONS
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BackgroundPrimary prevention of acute rheumatic fever requires antibiotic treatment of acute streptococcal pharyngitis. In developing countries, clinicians must rely on clinical guidelines for presumptive treatment of streptococcal pharyngitis since bacterial culture and rapid diagnostic tests are not feasible. We evaluated the WHO Acute Respiratory Infection guideline in a large urban paediatric clinic in Egypt.MethodsChildren between 2 and 13 years of age who had a sore throat and pharyngeal erythema were enrolled in the study. Clinical, historical, and demographic information was recorded and a throat culture for group A β-haemolytic streptococci was done. Sensitivity (% of true-positive throat cultures) and specificity (% of true-negative throat cultures) were calculated for each clinical feature. The effect of various guidelines on correct presumptive treatment for throat-culture status was calculated.FindingsOf 451 children with pharyngitis, 107 (24%) had group A β-haemolytic streptococci on throat culture. A purulent exudate was seen in 22% (99/450) of these children and this sign was 31% sensitive and 81% specific for a positive culture. The WHO Acute Respiratory Infections (ARI) guidelines, which suggest treatment for pharyngeal exudate plus enlarged and tender cervical node, were 12% sensitive and 94% specific; 13/107 children with a positive throat culture would correctly receive antibiotics and 323/344 with a negative throat culture would, correctly, not receive antibiotics. Based on our data we propose a modified guideline whereby exudate or large cervical nodes would indicate antibiotic treatment, and this guideline would be 84% sensitive and 40% specific; 90/107 children with a positive throat culture would correctly receive antibiotics and 138/344 with a negative throat culture would, correctly, not receive antibiotics.InterpretationThe WHO ARI clinical guideline has a high specificity but low sensitivity that limits the unnecessary use of antibiotics, but does not treat 88% of children with a positive streptococcal throat culture who are at risk of acute rheumatic fever. A modified guideline may be more useful in this population. Prospective studies of treatment guidelines from many regions are needed to assess their use since the frequency of pharyngitis varies.
Throat culture
Throat
Sore throat
Guideline
Microbiological culture
Acute Pharyngitis
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Throat
Throat culture
Carriage
Group A
Group B
Positive predicative value
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A total of 6,093 respiratory and febrile illnesses experienced by children were analyzed with regard to symptoms. Our objective was to devise simple guidelines that would allow for the detection of most clinical group A streptococcal infections while eliminating the need for taking throat cultures in the majority of nonstreptococcal illnesses. The results of the analysis led to the recommendation that throat cultures be taken in all illnesses with pure or predominant sore throat and fever of any degree and also in all other illnesses with an oral temperature of 101°F or higher even in the absence of sore throat. Application of these guidelines would have involved taking throat cultures in 29.5% of the 6,093 illnesses observed and would have detected 88.1% of 469 clinical group A streptococcal infections estimated to be capable of causing an antistreptolysin O response and therefore potentially capable of causing rheumatic fever. The need for taking cultures in 70.5% of the 6,093 illnesses would have been obviated. An additional 376 subclinical group A streptococcal infections capable of producing an antistreptolysin O response were observed in this study. Because of absence of symptoms these infections ordinarily would not have been detected.
Sore throat
Throat
Throat culture
Subclinical infection
STREPTOCOCCAL INFECTIONS
Group A
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