Evaluation of the Directigen 1,2,3 Group A Strep Test for diagnosis of streptococcal pharyngitis.

The Directigen 1,2,3 Group A Strep Test (DGAST; BBL Microbiology Systems, Cockeysville, Md.) was compared with conventional culture methods for the detection of group A streptococci. Among 327 children, the DGAST has a sensitivity of 75.0%, a specificity of 99.1%, and positive and negative predictive values of 97.5 and 89.3%, respectively, as compared with 48-h culture results. The lower sensitivity (60.0%) in 322 adults was related to the low incidence of group A streptococcal pharyngitis in that population (7.8%). The positive and negative predictive values for adults were 93.8 and 96.7%, respectively. Only 3 of 327 (0.9%) pediatric and 2 of 322 (0.6%) adult specimens yielded uninterpretable results in the DGAST.     

Comparison of Directigen Group A Strep Test with a traditional culture technique for detection of group A beta-hemolytic streptococci.

The Directigen Group A Strep Test (DGAST), a new rapid method of detecting group A beta-hemolytic streptococci directly from throat swabs, was compared with a traditional culture technique for the detection of group A beta-hemolytic streptococci. Five hundred oropharyngeal swabs from pediatric and adult patients were cultured and then processed by using the DGAST. Of the 144 specimens positive by culture, 131 were DGAST positive (sensitivity, 90.9%). Of the 356 specimens negative by culture, 353 were DGAST negative (specificity, 99.2%). Twelve of the 13 false-negative DGAST results were from pediatric patients. One hundred isolates of non-group A beta-hemolytic streptococci were recovered, primarily groups C, F, and G. The DGAST is easy to perform, rapid, sensitive, and very specific for detection of group A beta-hemolytic streptococci directly from swabs. Supplementing the DGAST with a culture on a 5% sheep blood agar plate would enhance detection of group A beta-hemolytic streptococci, especially in pediatric patients.     

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.     

Comparison of the Directigen 1-2-3 Group A Strep Test with culture for detection of group A beta-hemolytic streptococci.

The Directigen 1-2-3 Group A Strep Test (DGAST; BBL Microbiology Systems, Cockeysville, Md.) was compared with conventional culture procedures on Trypticase soy agar with 5% sheep blood (BBL) and Selective Streptococcal Agar (ssA; BBL) for detection of group A beta-hemolytic streptococci (GABHS) for 1,006 patients complaining of sore throat. The DGAST was performed at five acute-care clinics according to the instructions of the manufacturer; interpretation of the cultures was done at the central microbiology laboratory. Of 924 patients with complete data, 243 (26.3%) were positive for GABHS on culture when both sheep blood agar and ssA were used. Of the patients with positive cultures, 159 were detected by the DGAST, yielding a sensitivity of 65.4%, a specificity of 84.7%, a positive predictive value of 60.5%, and a negative predictive value of 87.3%. The greater the number of colonies on culture, the greater the sensitivity of the DGAST, and the more intense the positive reaction on the DGAST, the higher the positive predictive value of the test. For the identification of GABHS, sheep blood agar was superior to ssA by 12.9% at 24 h and by 3.4% at 48 h of incubation.     

Evaluation of the Culturette Brand Ten-Minute Group A Strep ID technique.

A direct extraction of the antigens of group A beta-hemolytic streptococci from 557 throat swabs was performed by a new microtechnique of the nitrous acid extraction method with the Culturette Brand Ten-Minute Strep ID technique from Marion Scientific, Division of Marion Laboratories, Inc., Kansas City, Mo. This group A latex reagent kit contains the reagents for the micronitrous acid extraction of throat swabs and does not require a centrifugation step in its protocol. There was a 99.3% (553 of 557) total agreement between the direct nitrous acid extraction-latex agglutination method and the standard culture method. The direct extraction method yielded an identification of 95.1% (78 of 82) of the group A streptococci identified by the standard method. Throat swabs used for standard culture may also be extracted with nitrous acid for the detection of group A antigen. A 5-min nitrous acid extraction destroys the viability of bacteria associated with normal throat flora as well as group A streptococci and Mycobacterium tuberculosis. This highly rapid method is simple to perform and requires no costly instrumentation. Accordingly, it would be most applicable in a hospital laboratory as well as in a physician's office.     

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.     

Evaluation of the RIDAQuick norovirus immunochromatographic test kit

Background

Norovirus infections occur frequently and are widespread throughout the US population causing greater than half of all foodborne gastroenteritis cases. A rapid norovirus assay would be a useful clinical tool for identification of this common virus in gastroenteritis patient samples, thereby identifying outbreaks and facilitating rapid implementation of control measures.

Objectives

To determine the suitability of the RIDAQuick norovirus kit as a clinical tool by determining the specificity and sensitivity of the assay, and its cross-reactivity with other enteric viruses.

Study design

Archived stool specimens containing norovirus genogroup I or II or other viruses were tested using the RIDAQuick norovirus assay and results compared to those obtained with real-time RT-PCR.

Results

We tested 62 samples: 19 norovirus genogroup I, 25 genogroup II samples, and 18 norovirus negative samples. Compared to PCR results, RIDAQuick assay sensitivity was 61.4%, and specificity was 100%. The low sensitivity was mainly due to poor results with genogroup I specimens; only 11 of 19 were detected. Additionally, samples of four other common enteric viruses all tested negative with the RIDAQuick assay.

Conclusions

The RIDAQuick kit effectively detects norovirus genogroup II strains, but not genogroup I strains. We found no cross-reactivity with several common enteric viruses. As most norovirus cases are currently genogroup II strains, positive results with RIDAQuick can be used for rapid detection of norovirus in a large percentage of cases, thus also aiding in identification of outbreaks. However, final confirmation and negative results require further testing with more sensitive methods.     

Evaluation of the Becton Dickinson Directigen test for respiratory syncytial virus in nasopharyngeal aspirates.

A premarket trial of the Becton Dickinson Directigen respiratory syncytial virus membrane-based enzyme immunoassay compared the test with virus isolation for the detection of respiratory syncytial virus in 583 nasopharyngeal aspirates. After modification, the Directigen test showed a sensitivity of 83% and a specificity of 90%. It offers the potential for an efficient bedside test--without the need for any equipment--for the diagnosis of respiratory syncytial virus infection and requires only a 0.25-ml sample volume. However, for optimum reliability, freezing-thawing of samples and access to a confirmatory test were shown to be necessary.     

Evaluation of Copan swabs with liquid transport media for use in the Gen-Probe Group A Strep Direct Test

The Gen-Probe Group A Streptococcus Direct Test (GASDT), which detects the presence or absence of group A streptococci directly from pharyngeal specimens, utilizes a specific relative light unit (RLU) cutoff of 4,500 to differentiate between positive and negative test results. In response to a report by a manufacturer that the background RLU values for the Copan rayon swabs with liquid media were higher than the RLU values typically observed with Culturette swabs, we tested multiple lots of Copan rayon swabs with liquid media and determined that the swabs are unacceptable for routine use in the GASDT. The high background RLU values for the Copan rayon swabs appear to be a direct result of the gamma irradiation used to sterilize the swabs. We also performed a comparative clinical evaluation of Copan Dacron swabs with liquid media and Culturette swabs for use in the GASDT. Overall, there was 97.5% agreement between the results obtained with the Copan Dacron swabs and those obtained with the Culturette swabs. Compared to Culturette swabs, the Copan Dacron swabs had a sensitivity and a specificity of 97 and 98%, respectively. Copan Dacron swabs with liquid media are an acceptable alternative to the swabs currently qualified for use with the GASDT, but Copan rayon swabs with liquid transport media should not be used in the GASDT.     

Evaluation of the Lyra Direct Strep Assay To Detect Group A Streptococcus and Group C and G Beta-Hemolytic Streptococcus from Pharyngeal Specimens

The Lyra Direct strep assay was compared to culture for its ability to detect Streptococcus group A and β-hemolytic groups C/G using rapid antigen-negative pharyngeal specimens (n = 161). The Lyra assay correctly detected all β-hemolytic streptococci (group A, n = 19; group C/G, n = 5). In batch mode, the Lyra assay reduced intralaboratory turnaround time by 60% (18.1 h versus 45.0 h) but increased hands-on time by 96% (3 min 16 s versus 1 min 40 s per specimen).     

Evaluation of the Rapid ID 32 Strep system

Objectives: To evaluate the performance of the Rapid ID 32 Strep system in the hands of clinical microbiologists without expert knowledge of streptococci or enterococci.
Methods: One hundred and twenty-two strains of streptococci and enterococci conventionally identified in a reference laboratory were sent under code numbers to a clinical microbiology laboratory and identified with the Rapid ID 32 Strep system.
Results: Regardless of whether automatic reading and identification or visual reading with identification using tables were done, 75–77% of the 122 examined strains were correctly identified, 7% were misidentified and 16–18% could not be identified with certainty to the species level. The system correctly identified the majority of the examined pyogenic streptococci and enterococci, but only two-thirds of the viridans streptococcal strains.
Conclusions: In a routine laboratory, the Rapid ID 32 Strep system can be used to give a rapid preliminary identification of streptococci and enterococci, but with viridans streptococci one would have to accept a certain risk of misidentification. The assay can, however, be used to biotype viridans streptococci in order to attempt to establish identity between separate isolates, e.g. from blood in patients suspected of having endocarditis.     

Use of swabs without transport media for the Gen-Probe Group A Strep Direct Test

For several years we used rayon or Dacron swabs with liquid transport media for collection and transport of throat swab specimens for testing with the Gen-Probe Group A Strep Direct Test (GASDT). A report of favorable results with a Dacron swab without any transport media for GASDT by another laboratory prompted us to compare detection of group A streptococci (GAS) with and without transport media (referred to as "wet" and "dry" swabs, respectively). Phase one of this study used swabs seeded with GAS. Initially, six recent clinical isolates of GAS were inoculated onto wet and dry swabs and stored at room temperature (RT). After 1, 2, and 3 days of storage, colony counting and GASDT were performed with the swabs. The results, expressed as the mean percentage of the results at zero time, were as follows: for GASDT with wet swabs at 1, 2, and 3 days, 62, 51, and 56%, respectively; for GASDT with dry swabs at 1, 2, and 3 days, 105, 80, and 85%, respectively; for colony counts with wet swabs at 1, 2, and 3 days, 52, 26, and 13%, respectively; for colony counts with dry swabs at 1, 2, and 3 days, 10, 0, and 0%, respectively. An additional six strains of GAS were tested in a similar manner, except that extracts of pharyngeal flora (PF) were added to the inocula. The results obtained with extracts of PF were comparable to those obtained with GAS alone. We also compared the performance of GASDT with wet and dry swabs stored at RT and 4 degrees C. Ten strains of GAS were inoculated onto wet and dry swabs, and GASDT was performed each day for 9 days. The GASDT results for swabs on day 9, expressed as the mean percentage of the results obtained at zero time, were as follows: dry swab and 4 degrees C, 59%; wet swab and 4 degrees C, 31%; dry swab and RT, 33%; and wet swab and RT, 19%. In phase two of this study we conducted a clinical evaluation to determine whether the differences observed with seeded specimens would also be evident with patient specimens. We used a single dry Dacron swab paired with a single rayon Bacti-Swab with liquid Stuart transport medium for the clinical evaluation. Specimens were collected from 1,005 outpatients, plated onto a Strep Selective Agar plate, and then tested within 30 min by GASDT. If culture of GAS from the same swab is used to define a true-positive test result, the sensitivities and specificities were as follows: GASDT with wet swabs, 86.2 and 98.5%, respectively; GASDT with dry swabs, 90.7 and 98.1%, respectively. However, the use of culture as the "gold standard" may understate the actual performance characteristics of GASDT, particularly for the dry swabs. In conclusion, for GASDT the use of swabs without transport media may be preferable to the use of swabs with transport media.     

Evaluation of a test kit for identification of anaerobic bacteria

A test kit for identification of anaerobic bacteria-API-has been compared for accuracy in individual tests and for identification on the genus or species level with pre-reduced anaerobically sterilized media methods on 241 anaerobic strains. The microsystem was found to be reliable and permits identification of the clinically most significance anaerobic bacteria if it is supplemented with other tests such as gaschromatographic analysis, morphology, lecithinase, lipase and antibiotic sensitivity pattern.     

Evaluation of the Binax NOW, BD Directigen, and BD Directigen EZ assays for detection of respiratory syncytial virus

The Binax NOW assay (Binax, Inc., Portland, Maine) and the BD Directigen EZ assay (Becton Dickinson and Company, Sparks, Md.), two new rapid immunoassays for detection of respiratory syncytial virus (RSV), as well as the BD Directigen RSV assay (DRSV) (Becton Dickinson and Company) and direct immunofluorescence staining (DFA) were compared with culture for detection of RSV in fresh specimens from both children and adults during the 2002-2003 respiratory virus season. The majority (95%) of specimens were nasal or nasopharyngeal washes or aspirates. A total of 47 (26%) were culture positive for RSV. The overall sensitivities of DFA (n = 149), NOW (n = 118), EZ (n = 88), and DRSV (n = 180) compared with culture (n = 180) were 93, 89, 59, and 77%, respectively. The specificities of DFA, NOW, EZ, and DRSV were 97, 100, 98, and 96%, respectively. However, when results were separated into those from children and those from adults, DFA was the only rapid test adequate for detection of RSV (sensitivity of 100% compared to 0, 0, and 25% for NOW, EZ, and DRSV, respectively) in adults. For children the sensitivities of DFA, NOW, EZ, and DRSV were 93, 94, 72, and 81%. The NOW assay was the most sensitive and specific and the easiest to perform of the kit tests for detecting RSV in children. None of these three rapid kit tests was sensitive for detecting RSV in specimens from adults. DFA remains the rapid method of choice for detecting RSV in the adult population.     

TestPack Strep A kit for the rapid detection of group A streptococci on 11,088 throat swabs in a clinical pathology laboratory.

Results obtained with Abbott Laboratories' TestPack Strep A, a rapid test kit to detect group A streptococcal antigen on throat swabs, were compared with the culture results. All tests were performed by American Society of Clinical Pathology-registered technologists in a large clinical laboratory. A total of 11,088 throat swabs were tested; 9,161 belonged to pediatric patients and 1,927 to adults. For TestPack Strep A, the study demonstrated a sensitivity value of 0.91 and a specificity value of 0.96; positive predictive value and negative predictive values were 0.82 and 0.98, respectively. These data indicate that even when performed by experienced technologists, in a laboratory setting, approximately 1 of 10 patients with group A streptococcal tonsillopharyngitis will be missed if physicians rely solely on this direct antigen test. A backup culture on all patients who are negative by a rapid antigen detection test is recommended.     

Multicenter Clinical Evaluation of the Novel Alere i Strep A Isothermal Nucleic Acid Amplification Test

Rapid detection of group A beta-hemolytic streptococcus (GAS) is used routinely to help diagnose and treat pharyngitis. However, available rapid antigen detection tests for GAS have relatively low sensitivity, and backup testing is recommended in children. Newer assays are more sensitive yet require excessive time for practical point-of-care use as well as laboratory personnel. The Alere i strep A test is an isothermal nucleic acid amplification test designed to offer highly sensitive results at the point of care within 8 min when performed by nonlaboratory personnel. The performance of the Alere i strep A test was evaluated in a multicenter prospective trial in a Clinical Laboratory Improvement Amendments (CLIA)-waived setting in comparison to bacterial culture in 481 children and adults. Compared to culture, the Aleri i strep A test had 96.0% sensitivity and 94.6% specificity. Discrepant results were adjudicated by PCR and found the Alere i strep A test to have 98.7% sensitivity and 98.5% specificity. Overall, the Alere i strep A test could provide a one-step, rapid, point-of-care testing method for GAS pharyngitis and obviate backup testing on negative results.     

Evaluation of the rapid Patho Dx Latex Strep Grouping Kit.

A variety of clinical specimens from throat, nose, ear, eye, wounds, urine, and vagina were collected, cultured, and screened for beta-hemolytic streptococci. The Patho Dx Latex Strep Grouping Kit (Diagnostic Product Corp., Los Angeles, Calif.) technique was applied to colonies taken right from the primary cultures. Isolated strains were sent to the reference laboratory where they were grouped by standard techniques. The kappa coefficient of agreement between the Patho Dx Kit and the standard method was 0.958. We believe that, although better agreement was achieved by others with isolated colonies, a very good agreement is also achieved with primary cultures. The fact that the laboratory is able to report an accurate answer after only 24 h seems most advantageous.