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.     

Sore throat in family practice: comparison of blood agar throat culture with a rapid enzyme immunoassay test for diagnostic purposes.

The Ventrescreen (Ventrex) rapid enzyme immunoassay test for detecting group A streptococcal antigen directly from a throat swab was compared with conventional blood agar throat culture in the diagnosis of beta haemolytic streptococcal infection among 311 patients with a sore throat attending a large suburban Jerusalem primary care clinic. Using the throat culture as the 'gold standard' the Ventrescreen test had a sensitivity of 82%, a specificity of 50%, a positive predictive value of 49%, and a negative predictive value of 82% for beta haemolytic streptococcal infection. These results are not good enough for the test to be considered a reliable substitute for throat culture in such a setting. The negative predictive value, however, supports the use of a negative test result to identify those patients in whom antibiotic therapy could be withheld until the result of their throat culture became available. These conclusions are at variance with recommendations from other studies of similar tests in different population groups, and stress the need for the careful evaluation, especially in primary care clinics, of any such rapid test which claims to be able to replace throat culture in the detection of beta haemolytic streptococcal infection.     

Do patients with sore throat benefit from penicillin? A randomized double-blind placebo-controlled clinical trial with penicillin V in general practice.

BACKGROUND: The effect of antibiotic therapy in sore throat is questionable and this dilemma has been complicated by the emergence of multiple resistant strains of micro-organisms. AIM: A randomized double-blind placebo-controlled clinical trial was undertaken in patients aged 4-60 years to assess the efficacy of penicillin V on the clinical course and bacteriological response in patients with sore throat in general practice. METHOD: Two hundred and thirty-nine patients presenting with an acute sore throat to 37 general practices in the Netherlands who were clinically suspected of group A beta-haemolytic streptococci (GABHS) were randomized for treatment with penicillin V (n = 121) or placebo (n = 118). Resolution of sore throat, fever and return to daily activities were evaluated by the general practitioner 2 days after the start of treatment and by the patients keeping a diary for 7 days. The result of throat culture after 2 days was evaluated. RESULTS: A difference in resolution of sore throat was present after 2 days in all patients, but was a result of GABHS-positive patients (n = 111; 46%) in favour of those randomized for penicillin V (adjusted odds ratio 5.3; 95% CI 1.9-15.1). An effect in the course of fever was also seen in GABHS-positive patients (adjusted odds ratio 5.3; 95% CI 1.02-27.7). A difference of 1-2 days was seen in clinical recovery. No difference was found in daily activities between the treatment groups. After 2 days, 4% of the penicillin-treated patients harboured GABHS compared with 75% of the placebo group. CONCLUSION: Only GABHS-positive patients benefit from penicillin V in their clinical cure in the first few days. Therefore, rapid testing is necessary. Treatment may be beneficial with regard to the clinical course, but it is not necessary.     

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.     

Comparison of illumigene Group A Streptococcus Assay with Culture of Throat Swabs from Children with Sore Throats in the New Zealand School-Based Rheumatic Fever Prevention Program

Group A streptococcal (GAS) pharyngitis is a particularly important condition in areas of New Zealand where the incidence of acute rheumatic fever remains unacceptably high. Prompt diagnosis and treatment of GAS pharyngitis are cornerstones of the Rheumatic Fever Prevention Programme, but these are hindered by the turnaround time of culture. Tests with excellent performance and rapid turnaround times are needed. For this study, throat swabs (Copan ESwabs) were collected from schoolchildren self-identifying with a sore throat. Samples were tested by routine culture and the illumigene GAS assay using loop-mediated isothermal amplification. Discrepant results were resolved by retesting of the same specimen by an alternative molecular assay. Seven hundred fifty-seven throat swab specimens were tested by both methods. The performance characteristics of the illumigene assay using culture on blood agar as the “gold standard” and following discrepancy analysis were as follows: sensitivity, 82% and 87%, respectively; specificity, 93% and 98%, respectively; positive predictive value, 61% and 88%, respectively; and negative predictive value, 97% and 97%, respectively. In our unique setting of a school-based throat swabbing program, the illumigene assay did not perform quite as well as described in previous reports. Despite this, its improved sensitivity and rapid turnaround time compared with those of culture are appealing.     

Diagnosis of Helicobacter pylori infection in adult and pediatric patients by using Pyloriset, a rapid latex agglutination test.

Pyloriset (Orion Diagnostica, Espoo, Finland) is a rapid antibody test using latex particles coated with acid-extracted antigen of Helicobacter pylori. We evaluated its ability to predict infection in 100 adult patients and 50 pediatric patients referred for gastric endoscopy. Sixty of 65 H. pylori-infected adults were correctly identified by the test. There were 12 false-positive and 5 false-negative reactions seen. Pyloriset had a sensitivity of 92% and a specificity of 66%. The positive predictive value was 83% and the negative predictive value 82%. In contrast, sensitivity dropped to 36% in the pediatric patients and the positive predictive value was only 40%. Pyloriset could become an important alternative to other more time-consuming diagnostic tests for H. pylori-infected adult patients but is inadequate for diagnosis of pediatric H. pylori infection.     

A randomized controlled trial of antibiotics on symptom resolution in patients presenting to their general practitioner with a sore throat.

BACKGROUND: Sore throat is a common symptom presented to general practitioners (GPs), and there remains controversy about the appropriate use of antibiotics. AIM: To compare, in a randomized controlled trial, the effectiveness of penicillin, cefixime and placebo on symptom resolution in patients presenting with a sore throat in general practice. METHOD: Twenty-two GPs in Avon recruited 154 patients, aged 16-60 years, presenting to their GP with a sore throat, and for whom the GP would normally prescribe an antibiotic. Patients were randomized to one of three groups: penicillin V 250 mg four times a day; cefixime 200 mg daily; and placebo. Each was prescribed for five days. The main outcome measures were a diary of symptom resolution over seven days and eradication of group A beta-haemolytic streptococcus (GABHS). RESULTS: Of the 103 (67%) patients who completed symptom diaries, 40 were allocated to receive penicillin, 29 cefixime and 34 placebo. In the analysis including all patients, symptom resolution was greater by day 3 in the cefixime group than in the placebo group. Penicillin did not improve symptom resolution by day 3 compared with placebo, and cefixime was not statistically significantly different from penicillin. There were significant differences in the proportion of patients using analgesia at day 3, with the proportion being lowest in the cefixime group. The results for the subgroup of patients without GABHS were similar to those for all patients; in particular, the only statistically significant difference was between cefixime and placebo. Although numbers were too small for statistical significance, among patients with GABHS the effects of penicillin and cefixime were similarly raised in relation to placebo. CONCLUSION: Compared with placebo, cefixime can improve the rate of resolution of symptoms in patients with a sore throat who are selected for antibiotic treatment by their GP. The unexpected finding that cefixime was of benefit compared with placebo for patients without GABHS suggests that bacteria other than GABHS may be important in the pathogenesis of sore throat.     

Comparative evaluation of two rapid Salmonella-IgM tests and blood culture in the diagnosis of enteric fever

Purpose: Enteric fever is a major public health problem in developing countries like India. An early and accurate diagnosis is necessary for a prompt and effective treatment. We have evaluated the diagnostic accuracy of two Rapid Salmonella-IgM tests (Typhidot-IgM and Enteroscreen-IgM) as compared to blood culture in rapid and early diagnosis of enteric fever. Materials and Methods: A total of 2,699 patients’ serum samples were tested by Rapid Salmonella-IgM tests and blood culture. Patients were divided into two groups. Test group—patients with enteric fever and blood culture positives for Salmonella Typhi; and three types of Controls, i.e. patients with non-enteric fever illnesses, normal healthy controls and patients positive for S. Paratyphi- A. In addition to this we have also evaluated the significance of positive Salmonella-IgM tests among blood culture-negative cases. Results: The overall sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the Typhidot-IgM test and Enteroscreen-IgM test considering blood culture as gold standard were 97.29% and 88.13%, 97.40% and 87.83%, 98.18% and 92.03%, 96.15% and 82.27%, respectively. Typhidot-IgM test was found to be significantly more sensitive and specific as compared to Enteroscreen-IgM. Among blood culture-negative patients, Rapid Salmonella-IgM tests detected 72.25% additional cases of enteric fever. Although the Rapid Salmonella-IgM tests are meant to diagnose S. Typhi only, but these tests detect S. Paratyphi- A also. Thirty-eight patients who were blood culture-positive for S. Paratyphi- A were also positive by Rapid Salmonella-IgM tests. Conclusion: Rapid Salmonella-IgM tests offer an advantage of increased sensitivity, rapidity, early diagnosis and simplicity over blood culture.     

Effect of medium and cultivation conditions on comparisons between latex agglutination and culture detection of group A streptococci.

In the laboratory diagnosis of pharyngitis, results from latex agglutination tests (LAT) performed directly on throat swabs are often compared with the isolation of group A beta-hemolytic streptococci (GABHS) from simultaneously obtained swabs cultivated on a variety of media under different atmospheric conditions. In this study, results of an LAT, Directigen, were compared with those of two different media: sheep blood agar (SBA) and group A selective strep agar (ssA). Specimens inoculated on SBA were incubated in three different atmospheres: air, 3 to 5% CO2, and anaerobically. Those inoculated on ssA were incubated in 3 to 5% CO2 only. Isolation of GABHS was confirmed by coagglutination. The standard for true positivity was the isolation of GABHS from at least one of the simultaneous cultures. Comparisons were made with samples from 693 adult patients. GABHS was isolated on at least one of the three cultures in 143 patients, demonstrating an isolation rate of 20.6%. LAT exhibited a sensitivity of 95.1%. SBA incubated in air, in CO2, or anaerobically had sensitivities of 86.2, 85.9, and 93.7%, respectively. The ssA detected 99.3% of the positive specimens. Single SBA culture proved to be inferior to LAT and therefore was a poor standard for measuring LAT performance. Single ssA cultures demonstrated the greatest sensitivity in GABHS detection and therefore could serve as a standard for measuring LAT performance.     

Standardization of fungal polymerase chain reaction for the early diagnosis of invasive fungal infection

Background: An early initiation of antifungal therapy in invasive fungal infections (IFIs) is critical in reducing the high mortality rate. Current diagnosis of fungal infection relies on microscopy, culture, antigen, antibody specific tests and histological diagnosis. However, these tests either lack sensitivity or specificity. There is thus the need for a rapid, specific and accurate diagnostic method. Objective: The aim of our study was to establish PCR for the rapid detection of Candida and Aspergillus species in clinical specimens with improved sensitivity and specificity. Materials and Methods: A total of 71 proven cases of IFI (confirmed by culture) were collected. A total of 15 healthy, 15 patients suffering from bacterial sepsis and 15 patients with HIV, HBV viral infections were included as controls. Clinical specimens were subjected to a standardized nested amplification to produce Round I (504 bp) and Round II (150 bp) amplicons. Restriction digestion was performed on these products for further identification. Results: Analytical sensitivity was determined using 10⁶–10 CFU/ml of cell suspension. The lower detection limit of the assay was 10 CFU/ml of blood. This test was 100% sensitive and specific with a positive predictive value of 100% and a negative predictive value of 96.7%. Conclusion: The assay was found to be effective for the rapid detection of Candida and Aspergillus in clinical specimens.     

Serologic Diagnosis of Helicobacter pylori Infection in Outpatients Aged 45 Years or Less

The diagnostic accuracy of serological tests for Helicobacter pylori was studied in 145 consecutive outpatients aged 45 years or less referred for gastroscopy. Helicobacter pylori infection can be detected by serological tests, including rapid whole-blood tests. The low prevalence of the disease in young people may have a negative effect on the positive predictive value of a test. In this study, the presence of Helicobacter pylori was assessed by a biopsy urease test and histological examination, and by several serological tests: a rapid whole-blood test on fingerstick blood, a latex agglutination serum test, a commercial enzyme immunoassay (EIA) test, and an in-house EIA for detection of antibodies of both the IgG and IgA classes. Helicobacter pylori infection was diagnosed with invasive tests in 21 (14.5%) patients. The sensitivity, specificity, and positive and negative predictive values of the EIA-based tests, compared to histological examination, were 100%, 96-97%, 81-84%, and 100%, respectively. The positive predictive value of the latex agglutination test was 78%, whereas it was only 47% for the whole-blood rapid test used. Although the results of the whole-blood rapid test were unsatisfactory, the quantitative EIA-based tests could reliably detect Helicobacter pylori among young patients, in whom the prevalence of the infection is low.     

Review of Rapid Diagnostic Tests for Influenza

Influenza is unique among viral infections because of its propensity for seasonal epidemics and occasional pandemics, and because of the morbidity and mortality that result from its pulmonary complications. In contrast to the majority of viruses, effective well-tolerated influenza vaccines, antivirals and chemoprophylaxis are available. The need for a timely diagnosis, which allows for optimal use of these treatments, led to the introduction of numerous rapid diagnostic tests (with turnaround times of less than 30 minutes). However, during influenza season, clinical diagnosis (based on cough and high fever of acute onset) can be highly predictive of influenza. Thus diagnostic tests are not required for all patients with suspected influenza but may be of value if the clinical diagnosis is unclear and if antiviral or antibiotic treatment is a consideration. When evaluating performance of various rapid diagnostic tests for influenza, it is important to consider the type and quality of specimen and type of patient to be tested. Specimen-type drives performance of the rapid diagnostic tests. Swab specimens, particularly throat swabs are the most frequently submitted but least desirable specimen-type. Thus, although current rapid diagnostic tests are specific for influenza, sensitivity is highly variable. To improve diagnostic accuracy, a nasal/nasopharyngeal aspirate or sputum specimen should be obtained. Because of their highly variable sensitivity and negative predictive value, it is our opinion, that rapid diagnostic tests should only be used in influenza season and that results should be confirmed with virus culture. Despite these reservations, during influenza-season, detection of influenza by rapid diagnostic test may, potentially, be of great benefit to the patient and public health.     

Detection ofMycobacterium tuberculosis complex in clinical specimens by a commercial polymerase chain reaction kit

A total of 722 respiratory and 86 nonrespiratory specimens obtained from 456 patients were tested for detection ofMycobacterium tuberculosis complex by a commercial polymerase chain reaction (PCR) kit (Amplicor, Roche Diagnostic Systems) and the results compared with those of microscopy and culture (solid and radiometric media). Respiratory and nonrespiratory specimens were analysed separately. Of the respiratory specimens, 54 were positive forMycobacterium tuberculosis complex both in the PCR and in culture, five were positive in the PCR but negative in culture, and eight were positive in culture but negative in the PCR. Four cultures were positive for mycobacteria other thanMycobacterium tuberculosis; none of these gave a positive result in the commercial test. Resolution of discrepant results was performed by analysis of patients' clinical data. For respiratory specimens the sensitivity of the commercial test was 87.6%, the specificity 99.6%, the positive predictive value 96.6%, and the negative predictive value 98.7%. For nonrespiratory specimens the sensitivity was 60%, whereas the specificity ranged as high as 98.6%. For this group the positive predictive value was 85.7% and the negative predictive value 94.9%. When respiratory specimens are used, the commercial PCR test for detection ofMycobacterium tuberculosis complex, with its high sensitivity and specificity, is a good complementary diagnostic tool for rapid diagnosis of bronchopulmonary tuberculosis in a routine mycobacterial laboratory.     

A comparison of Thermo Electron RSV OIA to viral culture and direct fluorescent assay testing for respiratory syncytial virus.

BACKGROUND: Rapid diagnostic methods for respiratory syncytial virus are useful tools available for the clinician. OBJECTIVES: The Thermo Electron RSV OIA (optical immunoassay kit) was prospectively compared with direct immunofluorescent assay and viral culture at Primary Children's Medical Center, Salt Lake City, Utah. STUDY DESIGN: Specimens from three hundred and thirty patients exhibiting respiratory symptoms were collected for testing by the three methods above. Several specimens were positive by both OIA and DFA with a negative culture result. These culture results were verified by RT-PCR analysis. RESULTS: Overall, 107 specimens were positive for RSV by the reference tests (culture or RT-PCR). DFA analysis identified an additional 40 patient specimens positive for other respiratory viruses. Compared to the reference tests the sensitivity, specificity, positive, and negative predictive values of the OIA for detection of RSV were 87.9%, 99.6%, 98.9% and 94.5%, respectively. CONCLUSIONS: The rapid OIA assay format proved to be cost effective, and simple to use in comparison to DFA and viral culture. Negative rapid test results should still be confirmed with a secondary test.     

Comparison of three serological methods for diagnosing Mycoplasma pneumoniae infection.

AIMS--To compare the novel Serofast latex agglutination test (International Mycoplasma, Toulon-Cedex, France) with the complement fixation test and enzyme immunoassay (EIA) for diagnosing acute Mycoplasma pneumoniae infection. METHODS--Paired sera from 60 patients with respiratory infection who had tested positive for M pneumoniae by complement fixation test were analysed with Serofast and indirect EIA for specific IgG and IgM antibodies. RESULTS--Serofast was less sensitive than the two other tests. Only 30 (50%) out of 60 paired sera which showed a diagnostic seroconversion or had high positive, unchanged antibody titres by complement fixation test or EIA, or both, tested positive with Serofast. Positive test results with Serofast were associated with the presence of a complement fixation test titre of > or = 512 and high positive IgM antibody titres measurable by EIA; virtually all patients with a complement fixation test titre of < 256 or those responding primarily in the IgG class tested negative with Serofast. Based on analysis of sera taken at the acute phase of infection, 10 (17%) of the 60 patients tested positive by complement fixation test, 10 (17%) by EIA, and only four (7%) by Serofast. CONCLUSIONS--Serofast was less sensitive than complement fixation test and EIA and it cannot be recommended as a replacement for either test in routine diagnostic use. It might prove useful in laboratories where non-specific tests, such as the determination of cold agglutinins, are still used for the diagnosis of M pneumoniae infection. Testing paired sera is, however, a prerequisite for obtaining acceptable sensitivity by Serofast as well as other serological methods currently available.     

Diagnostic value of the Binax NOW assay for identifying a pneumococcal etiology in patients with respiratory tract infection.

BACKGROUND AND PURPOSE: Streptococcus pneumoniae is a common pathogen in respiratory tract infections which is usually underestimated with conventional tests, largely due to the fragility of the bacteria. This study assessed the diagnostic value of a rapid test (Binax NOW) for the detection of the pneumococcal antigen in urine. METHODS: Unconcentrated urine samples from 1243 adults and 91 children hospitalized with respiratory tract infections were tested. RESULTS: In all adults with respiratory tract infections, the diagnostic results were as follows: sensitivity, 29 (60%) of 48; specificity, 748 (92.2%) of 811; negative predictive value, 748 (97.5%) of 767; false-positive rate, 63 (68%) of 92. The diagnostic results were similar in adults with lower respiratory tract infections: sensitivity, 21 (64%) of 33; specificity, 658 (92.2%) of 714; negative predictive value, 658 (98.2%) of 670; false-positive rate, 56 (73%) of 77. In children with respiratory tract infections, the diagnostic results were: sensitivity, 4 of 4; specificity 18 (64%) of 28; negative predictive value, 18 of 18; false-positive rate, 10 of 14. The low specificity of the test in children may be due to frequent pneumococcal nasopharyngeal colonization. CONCLUSIONS: High negative predictive values and high false-positive rates were found in both adults and children, indicating that a negative result may be more useful than a positive one in clinical practice. The high specificity of this test in adults indicates its potential value in the choice of initial antibiotic treatment by eliminating pneumococcal infection as a likely cause of respiratory tract infection in a proportion of patients.     

EVALUATION OF A RAPID IMMUNOCHROMATOGRAPHIC DEVICE FOR THE DETECTION OF IgM & IgG ANTIBODIES TO DENGUE VIRUSES (DENV) IN A TERTIARY CARE HOSPITAL IN SOUTH INDIA

This study has evaluated the performance of a rapid immunochromatographic test (ICT) device in detecting antibodies to Dengue virus (DENV) in a tertiary hospital in South India. Sera from hospital attendees, with requests for DENV antibody testing, were tested with the Panbio Dengue Duo Cassette and a reference antibody capture assay for the detection of IgM (Dengue IgM capture ELISA-National Institute of Virology, India) and IgG (Dengue IgG capture ELISA-Panbio Diagnostics Inc., Australia) antibodies. The ICT results were compared with results of antibody capture tests for the detection of the IgM and IgG antibodies, respectively. Accuracy indices for IgM and IgG detection, respectively were - sensitivity 81.8% and 87.5%, specificity 75.0%, and 66.6%, positive predictive value (PPV) 61.0% and 72.9% and negative predictive value (NPV) 89.6% and 83.9%. The device performs poorly in detection of IgM and IgG antibodies to DENVs and is not recommended for use as a stand-alone diagnostic test.     

Comparison of the TestPack Strep A enzyme immunoassay system with anaerobically incubated cultures for detection of group A streptococci from oropharyngeal swabs

To find a rapid and sensitive test for detection of Group A streptococci (GABS), the performance of the TestPack Strep A (TPSA; Abbott) was compared with culture with the use of rayon-tipped throat swabs from symptomatic patients six months to 90 years of age. Each swab was first inoculated to a 5% sheep blood agar plate and then tested for GABS antigen with the use of the TPSA and the manufacturer's instructions. Cultures were incubated anaerobically at 35 degrees C for 36-48 hours unless positive results were obtained after one night. GABS were identified with a fluorescent antibody method or a latex antibody test. From 1,616 throat swabs, 296 (18.3%) of the cultures contained GABS. The sensitivity and specificity of the TPSA were 73.3% and 94.8%, respectively, whereas the predictive values of positive and negative results were 75.9% and 94.1%, respectively. Results varied significantly, however, with different production lots of TPSA. The TPSA does not appear to provide a sensitive alternative to an anaerobic culture for detection of GABS.