Fast diagnostic tests in the management of group A beta-heamolytic streptococcal pharyngitis

OBJECTIVE: Routine clinical diagnosis of Streptococcus pyogenes in pharyngitis is not always easy. The use in common practice of rapid diagnosis test (RDT), might offer a best control of the antibiotic treatments. The aim of this study is to present seven rapid diagnosis tests, to assess their feasibility and finally to determine the bacteriological correlation. METHOD: We propose to compare the results obtained with seven RDT, and to assess their interest in medical diagnosis for group A streptococcus pharyngitis. A prospective study was conducted for three months, a RDT was performed for children (n=75) between eight and fourteen years old presenting acute pharyngitis. Several throat sampling were performed to order cultures. RESULTS: The group A streptococcus was isolated in 33% (n=25) of throat sampling. Comparing cultures results, and for all studied tests, we obtained comparable performances with manufacturer data, specificity upper than 94% and sensitivity upper than 88%. CONCLUSION: All assessed RDT may offer to physicians a decision-making tool for rapid diagnosis. However, because of its complexity, the agglutination test can be used only in pathology laboratories.     

Rapid diagnosis of group A streptococcal antigen extracted directly from swabs by an enzymatic procedure and used to detect pharyngitis.

Coagglutination after enzymatic digestion is a widely used, rapid procedure for serogrouping isolated colonies of beta-hemolytic streptococci. We tried to determine whether the same procedure could be used for the detection of group A streptococcal antigen directly from swabs used to take throat samples. This was achieved by incubating the swabs immersed in a small quantity of lytic extract obtained from cultures of the Maxted strain of Streptomyces griseus and testing the supernatant fluid by coagglutination. Of 538 throat swabs tested, blindly comparing the results of conventional cultures and rapid antigen detection, both tests were negative in 480 and both were positive in 49 swabs. In six cases, culture was positive and the rapid test was negative, but only one swab was from a patient with acute pharyngitis. In three cases, cultures were negative but the rapid test showed a strongly positive reaction. No special instructions were given to the physicians taking the samples. We conclude that this rapid antigen detection test, giving results in approximately 1 h, is an economic and reliable procedure for the detection of group A streptococcal antigen directly from throat samples.     

Effect of clinical spectrum, inoculum size and physician characteristics on sensitivity of a rapid antigen detection test for group A streptococcal pharyngitis

We aimed to assess the independent effect of clinical spectrum, bacterial inoculum size and physician characteristics on the sensitivity of a rapid antigen detection test (RADT) for group A streptococcus (GAS) in children. Double throat swabs were collected from 1,482 children with pharyngitis and 294 asymptomatic children in a French prospective, office-based, multicenter (n?=?17) study, from October 2009 to May 2011. Patient- and physician-level factors potentially affecting RADT sensitivity were studied by univariate and multivariate multilevel analysis, with laboratory throat culture as the reference test. In children with pharyngitis and asymptomatic children, the prevalence of GAS was 38 % (95 % confidence interval 36–41 %) and 11 % (7–14 %), respectively. Overall, RADT sensitivity was 87 % (84–90 %). On stratified and multivariate multilevel analysis, RADT sensitivity was higher for children with pharyngitis than asymptomatic children (89 % vs. 41 %), children <9 than ≥9 years old (88 % vs. 79 %) and those with heavy than light inoculum (94 % vs. 53 %). RADT sensitivity was influenced by the physician performing the test (range 56–96 %, p?=?0.01) and was higher for physicians with hospital-based clinical activity in addition to office-based practice (adjusted odds ratio 3.4 [95 % confidence interval 1.9–6.3], p?<?0.001); inter-physician variations in RADT sensitivity were largely explained by this variable (proportional change in variance >99 %). The sensitivity of the RADT is independently affected by patient- and physician-level factors. Physicians who base their diagnosis of GAS pharyngitis on the results of a RADT alone should consider diagnostic accuracy monitoring and adequate training when needed.     

Rapid detection of group B streptococcal antigen in human amniotic fluid.

Infants exposed in utero to group B streptococcus (GBS)-infected human amniotic fluid (HAF) are at high risk for serious infection. Latex particle agglutination (LPA) tests are not approved for detection of GBS in HAF. Two LPA systems, Patho-Dx Strep B and Wellcogen Strep B, were used to test unfiltered sterile HAF and filtered HAF containing concentrations of GBS carbohydrate from 0.2 to 100 micrograms/ml. Four different processing techniques were used to prevent nonspecific LPA: EDTA, nitrous acid, enzyme, and nitrous acid-heat. GBS (10(2) CFU/ml) was inoculated into filtered HAF, incubated, sampled serially, processed with enzyme, and tested by LPA. Unprocessed, unfiltered HAF showed 33% nonspecific agglutination when tested by LPA. Processing of HAF removed nonspecific agglutination and improved GBS antigen detection. Without processing, LPA could not detect less than 100 micrograms of GBS carbohydrate per ml. With nitrous acid or enzyme processing, as little as 0.2 microgram/ml could be detected. Results were easier to read after enzyme processing than after nitrous acid processing. Although both LPA systems were equally efficient, testing was easier with the Patho-Dx system. After enzyme processing, LPA could detect as few as 10(4) CFU/ml when agglutination was read with a 4 X hand lens. Substances in HAF induce false-positive reactions during LPA testing. Processing removes the interference and improves the detection of GBS. LPA testing of HAF may allow earlier identification and treatment of infants at risk for serious GBS infection.     

Enzyme immunoassay for the detection of group A streptococcal antigen.

A competitive inhibition enzyme immunoassay for the detection of Streptococcus pyogenes directly from throat specimens or from solid bacteriological medium is described. Group A-specific polysaccharide adsorbed onto treated polystyrene beads, in conjunction with rabbit antibody to S. pyogenes, was used to determine the presence of the polysaccharide antigen. Inhibition values in excess of 65% were observed with 10(4) or more CFU of S. pyogenes per test. An inhibition of 25% was demonstrated with as few as 10(3) CFU per test. Heterologous microorganisms tested at 10(6) CFU per test reacted at levels of inhibition less than 25%. Two types of bacterial transport medium and swabs of different fiber compositions did not alter the assay performance. Accurate identification of S. pyogenes was achieved by testing single colonies picked directly from blood agar plates which had been incubated for 18 to 24 h. In addition, the assay was performed on throat specimens from children and adults having pharyngitis. A single-swab, blind study was conducted in which enzyme immunoassay reactivity was compared with results of blood agar culture and bacitracin sensitivity. When there were discordant results, serological identification was used as the confirmatory test. At an optimal cutoff value of 40% inhibition, sensitivity and specificity by enzyme immunoassay were 97.0% and 97.9%, respectively, as compared with confirmed culture results. The assay has an incubation time of 3 h and is a sensitive and specific method for the detection of S. pyogenes antigen.     

Rapid diagnosis of pharyngitis caused by group A streptococci

Although commercial rapid antigen detection tests (RADTs) are more expensive than blood agar plate (BAP) cultures, the advantage they offer is the speed with which they provide results. Rapid identification and consequent prompt treatment of patients with pharyngitis due to group A beta-hemolytic streptococci (GABHS) can reduce the risk of spread of GABHS, can allow patients to return to school or work sooner, and may reduce the acute morbidity of this illness. In most studies, RADTs have been compared with BAP cultures as the criterion standard. However, these comparisons are complicated by the fact that there is no universally accepted procedure for performing a BAP culture. The great majority of the RADTs that are currently available have a high specificity (i.e., 95% or greater) and a sensitivity of between 70 and 90% compared with BAP cultures. Few published studies have compared the performance of various RADTs to each other or examined the performance of various RADTs in the office setting. There is also relatively little published information about how physicians in practice actually use RADTs, but the available information suggests that many physicians do not follow recommended guidelines. While the development of easy-to-perform RADTs for the diagnosis of GABHS pharyngitis has altered clinical practice substantially, only limited data about cost-effectiveness are currently available.     

Comparison of two rapid latex agglutination methods for detection of group A streptococcal pharyngitis

Throat swabs from 404 patients with suspected pharyngitis were collected using duplicate swabs. Both swabs were used to inoculate 5% sheep blood agar plates, which were incubated in an anaerobic atmosphere for the isolation of Group A streptococci. The throat swabs were tested for the presence of Group A antigen using the Culturette Brand 10-Minute Group A Strep ID kit (Marion Scientific, Kansas City, MO), and the Direct Antigen Identification D.A.I. Strep A Test (Difco Laboratories, Inc., Detroit, MI). We found that 77 of the 404 specimens were culture positive for Group A streptococci. The Strep ID kit had a sensitivity of 83.7% and a specificity of 91.6%. The positive and negative predictive values were 72% and 95.6%, respectively. The D.A.I. test had a sensitivity of 80.2% and a specificity of 100%. The positive and negative predictive values were 100% and 94.5%, respectively. There was not a significant difference in the sensitivity of the two kits (P less than 0.1), but there was a significant difference in the specificity (P less than 0.01).     

Comparison of two rapid streptococcal antigen detection assays with culture for diagnosis of streptococcal pharyngitis.

In this study, 801 pharyngeal specimens were cultured for group A streptococci and tested with the Biostar Strep A Optical Immunoassay (Strep A OIA). The respective sensitivities and specificities were as follows: culture, 97.1 and 100%; Strep A OIA, 91.5 and 94.8%. Of the 801 specimens, 597 were also tested with the Abbott TestPack Strep A Assay (TP-ST). For those specimens tested by all three methods, the respective sensitivities and specificities were as follows: culture, 98.1 and 100%; Strep A OIA, 92.3 and 95.4%; and TP-ST, 79.4 and 100%. The Strep A OIA is significantly more sensitive than TP-ST and compares favorably with culture.     

Micronitrous acid extraction-coagglutination test for rapid diagnosis of streptococcal pharyngitis.

A micronitrous acid extraction-coagglutination test for the rapid diagnosis of streptococcal pharyngitis was examined in a busy pediatric clinic and found to be a simple, rapid, and inexpensive procedure with a sensitivity of 78% and a specificity of 98% when compared with blood agar culturing.     

Detection of group B streptococcal antigen in early-onset and late-onset group B streptococcal disease with the Wellcogen Strep B latex agglutination test.

The Wellcogen Strep B latex agglutination test (Wellcome Diagnostics, Dartford, England) was evaluated as a method of detecting group B streptococcal antigen in urine, cerebrospinal fluid, and serum from neonates with early-onset (less than or equal to 7 days of age) and late-onset group B streptococcal disease. Urine was the best source of antigen, which was detected in 100% of six neonates with early-onset group B streptococcal disease who had urine available in the first 12 h of illness and in 88% of 17 group B streptococcus-infected neonates with urine available in the first 48 h of illness. Antigen was not detected in any samples from patients without group B streptococcal disease except in the urine of one patient with Proteus mirabilis meningitis. The Wellcogen Strep B latex test of the lot tested compares favorably with a noncommercially available latex agglutination test.     

Toxic shock syndrome due to group A streptococcal pharyngitis and bacteremia in an adult

Bacteremia and/or toxic shock syndrome is a rare complication of streptococcal pharyngitis in adults. We describe a case of streptoccocal toxic shock syndrome in a previously healthy young man who presented with fatigue, high fever, and suspected extensive streptoccocal tonsillo-pharyngitis. Therapy consisted of high doses of antibiotics followed by treatment of consumptive coagulopathy, acute renal failure, and toxic shock syndrome. An attempt at hemodialysis and hemodiafiltration was ineffective, and the patient died 24 h after admission. The autopsy findings were compatible with the clinical diagnosis. The invasive group A streptococci isolated from the pharyngeal swab and blood cultures were identified as M1 and T1 type with pyrogenic exotoxin genes A and B. This was thus a definite case of streptococcal toxic shock syndrome complicated with multiorgan failure and lethal outcome. The benefit of intravenous immunoglobulins, surgical intervention, or clindamycin in survival improvement remains to be evaluated.     

A method for the preparation of a group specific psittacosis antigen for use in the complement fixation test

Summary A simple method for the preparation of group specific, potent and stable psittacosis antigen is outlined.Infected allantoic fluids rich in the elementary bodies of psittacosis agent are pooled, centrifuged at 20.000 r.p.m.; the sediment is resuspended in distilled water to 1/50th of its original volume and subjected to several cycles of ultrasonic vibration. After each cycle of vibration, the supernatant is collected and the resuspended sediment exposed to further ultrasonic treatment. The supernatant fluids with high complement fixing titres are pooled and used as an antigen. The titre of such an antigen ranges between 1:2000 and 1:8000. It is stable both at room temperature and 4°C for at least two years.     

Rapid detection of group B streptococcal antigen by monoclonal antibody sandwich enzyme assay.

Group B Streptococcus (GBS) is the most common cause of neonatal sepsis and meningitis. Infants at greatest risk to develop invasive disease are delivered to women colonized with GBS in their birth canals and lacking immunity to the colonizing serotype. We have investigated the sensitivity and specificity of a recently developed monoclonal antibody sandwich enzyme immunoassay for detection of GBS antigen. The sandwich enzyme immunoassay detected types II and III GBS at a concentration of 5 X 10(4) CFU/ml and types Ia and Ib GBS at 5 X 10(5) CFU/ml. No cross-reactions were noted when each of the GBS serotypes was reacted with antibodies of differing serotypes specificities. Type III GBS native antigen was detected at a concentration of 1 ng/ml. The sandwich enzyme assay is more sensitive than other methods currently in use for rapid detection of GBS and is serotype specific. This assay system should prove useful for the detection of GBS colonization during labor and for identification of neonates with invasive disease.     

Comparison of the Gen-Probe Group A streptococcus Direct Test with culture and a rapid streptococcal antigen detection assay for diagnosis of streptococcal pharyngitis.

The Gen-Probe Group A Streptococcus Direct Test (GP-ST) is a new assay which utilizes a nucleic acid probe to detect group A streptococci directly from pharyngeal swabs. In this study, 1,103 specimens were cultured and tested by GP-ST. The sensitivities and specificities were as follows: culture, 98.8 and 100%; GP-ST, 92.4 and 99.6%. Of the 1,103 specimens, 808 were also tested with the TestPack Strep A assay. For the specimens tested by all three methods, the sensitivities and specificities were as follows: culture, 99.5 and 100%; TestPack Strep A assay, 76.3 and 99.7%; GP-ST, 93.5 and 99.7%. The GP-ST is a very user-friendly assay which has the potential to replace culture for the diagnosis of streptococcal pharyngitis.     

Diagnostic accuracy of rapid nucleic acid tests for group A streptococcal pharyngitis: systematic review and meta-analysis

BackgroundAcute pharyngitis is one of the most common conditions in outpatient settings and an important source of inappropriate antibiotic prescribing. Rapid antigen detection tests (RADTs) offer diagnosis of group A streptococcus at the point of care but have limited sensitivity. Rapid nucleic acid tests (RNATs) are now available; a systematic review of their accuracy is lacking.ObjectivesTo evaluate the accuracy of RNATs in patients with pharyngitis; to explore test-level and study-level factors that could explain variability in accuracy; and to compare the accuracy of RNATs with that of RADTs.Data sourcesMEDLINE, Embase, Web of Science (1990–2020).Study eligibility criteriaCross-sectional studies and randomized trials.ParticipantsPatients with pharyngitis.Index test/s and reference standardsRNAT commercial kits compared with throat culture.MethodsWe assessed risk of bias and applicability using QUADAS-2. We performed meta-analysis of sensitivity and specificity using the bivariate random-effects model. Variability was explored by subgroup analyses and meta-regression.ResultsWe included 38 studies (46 test evaluations; 17 411 test results). RNATs were most often performed in a laboratory. The overall methodological quality of primary studies was uncertain because of incomplete reporting. RNATs had a summary sensitivity of 97.5% (95% CI 96.2%–98.3%) and a summary specificity of 95.1% (95% CI 93.6%–96.3%). There was low variability in estimates across studies. Variability in sensitivity and specificity was partially explained by test type (p < 0.05 for both). Sensitivity analyses limited to studies with low risk of bias showed robust accuracy estimates. RNATs were more sensitive than RADTs (13 studies; 96.8% versus 82.3%, p 0.004); there was no difference in specificity (p 0.92).ConclusionsThe high diagnostic accuracy of RNATs may allow their use as stand-alone tests to diagnose group A streptococcus pharyngitis. Based on direct comparisons, RNATs have greater sensitivity than RADTs and equal specificity. Further studies should evaluate RNATs in point-of-care settings.     

Detection of group A streptococcal antigen directly from throat swabs with a ten-minute latex agglutination test.

Using 490 strains of Staphylococcus aureus divided into methicillin-susceptible, -resistant, and -heteroresistant varieties, we compared the results obtained by the agar disk method with those obtained with the automated Autobac system. Susceptible strains exhibited a perfect correlation, whereas there were numerous discrepancies with resistant and still more with heteroresistant varieties. When incubation was increased to 18 h at 37 degrees C (Autobac incubation temperature), 35 degrees C, or 30 degrees C, these differences disappeared, but other problems may arise when incubation is prolonged, especially with erythromycin. We thus recommend carrying out two readings, a normal one after 3 h of incubation and a special reading after 18 h, solely for the detection of heteroresistance to methicillin.     

Selective streptococcal agar versus blood agar for detection of group A beta-hemolytic streptococci in patients with acute pharyngitis.

In a study on acute pharyngitis in general practice, we compared a selective group A streptococcal agar (ssA) for the recovery of group A beta-hemolytic streptococci (GABHS) with sheep blood agar. All plates were incubated at 36 degrees C in an atmosphere reinforced with 5% CO2 for 48 h with a first reading after 24 h. A total of 197 GABHS isolates were obtained from 721 throat cultures on both media. The recovery of GABHS was significantly higher after 48 h of incubation for both media. With the ssA plate, we detected significantly more GABHS after 24 h as well as after 48 h of incubation. The ssA plate reduced normal flora qualitatively and quantitatively. In conclusion, ssA is more sensitive and specific for the detection of GABHS than sheep blood agar and moreover easier to read. We recommend incubation for 48 h.