Comparison of the fluorescent treponemal antibody absorption (FTA-ABS) test with the FTA-ABS double staining test for detection of antitreponemal immunoglobulin M in the 19S fraction of human serum.

A widely used immunoglobulin M (IgM) detection assay for the diagnosis of neonatal congenital syphilis is the fluorescent treponemal antibody absorption test used with fractionated serum (FTA-ABS 19S IgM test). Reading the results of the FTA-ABS test is more cumbersome than reading those of the FTA-ABS double staining (FTA-ABS-DS) test, a confirmatory test for specific IgG. To verify that the FTA-ABS-DS test used with an anti-human IgM conjugate could detect specific IgM in fractionated serum samples (FTA-ABS-DS 19S IgM test), 164 fractionated (QUIK-SEP IgM Isolation System; ISOLAB, Inc., Akron, Ohio) serum specimens from infected neonates or adults or from IgG-seronegative subjects were tested by both techniques. The sensitivity limits of the two tests were assessed with reactive serum samples diluted to an endpoint titer. Samples nonreactive by the FTA-ABS 19S IgM test (n = 74) were either nonreactive (n = 65), minimally reactive (n = 5), or reactive (n = 4) by the FTA-ABS-DS 19S IgM test. Samples minimally reactive by the FTA-ABS 19S IgM test (n = 32) were minimally reactive (n = 1) or reactive (n = 31) by the double staining test. All samples reactive by the FTA-ABS 19S IgM test (n = 58) were also reactive by the FTA-ABS-DS 19S IgM test. There was a directly proportional linear relationship (r = 0.9794) between titers obtained by both tests. FTA-ABS-DS 19S IgM titers were constantly equal to or higher than FTA-ABS 19S IgM titers. Fluorescence intensity reading repeatability was 91.4% for the FTA-ABS-DS 19S IgM test and 81.7% for the FTA-ABS 19S IgM test (P = 0.015). Because the more easily read FTA-ABS-DS 19S IgM test is at least as sensitive as, if not more sensitive than, the FTA-ABS 19S IgM test, it is a good alternative to the latter test for the detection of specific IgM in human fractionated sera for those using fluorescence microscopes with incident light.     

Application of the soluble antigen fluorescent antibody (SAFA) test to the serodiagnosis of rabies.

The adaptation and evaluation of the Soluble Antigen Fluorescent Antibody (SAFA) test for the serologic diagnosis of rabies is described. Evaluation of the SAFA test was based on a comparison between serum titers obtained in the SAFA test, the mouse Serum Neutralization (SN) test and in the Indirect Fluorescent Antibody (IFAT) test. Dog, fox, raccoon and skunk sera were used for the comparison with mouse SN titers. Human serum was used for the comparison with the IFAT titer. The purity and concentration of the test antigen is a crucial factor in determining the efficiency of the SAFA test for rabies serodiagnosis. Viral antigen obtained by the AIPO4 gel method for rabies virus purification and concentration was found to be sufficiently purified and concentrated for use in the SAFA test. Conjugate dilution decreased the level of non-specific staining. Although specific activity was also decreased, there was a statistically significant difference (P less than or equal to 0.05; Student's t test) between the rabies positive and the rabies negative serum samples at all conjugate dilutions for all species studied. In three cases (fox, raccoon, skunk) SAFA titers were greater than mouse SN titers. In one case (dog) the SAFA titer was less than the mouse SN titer. The IFAT titer of the human serum sample was greater than the SAFA titer. Comparison of Fluorometer Dial Readings (FDR) of sera obtained in separate protocols demonstrated satisfactory reproducibility of the SAFA test for rabies serodiagnosis.     

Evaluation of automated large-scale screening tests for syphilis.

Two methods of performing serological screening tests for syphilis are compared. One consisted of the Venereal Diseases Reference Laboratory (VDRL) slide test, the cardiolipin Wassermann reaction (CWR), and the Reiter protein complement fixation test (RPCFT) performed manually; the other was a fully automated system using two Technicon AutoAnalyzers (AAII), one for the automated reagin test (ART) and the other for automated complement fixation tests. The absorbed fluorescent treponemal antibody test (FTA-ABS) was used as a final arbiter in all cases found to be seropositive by either method. A pooled antigen consisting of a mixture of cardiolipin and Reiter protein was used for the automated complement fixation test, thus increasing the scope and capacity of the system. The AutoAnalyzer was shown to be capable of performing 400 cardiolipin and Reiter complement fixation tests and 700 automated reagin tests in an 8-hour day. Modification of the complement fixation test method to take advantage of the highly sensitive colorimeter resulted in a significant increase in sensitivity and a corresponding saving in reagents. Of the 7843 sera tested, 258 gave a positive result in one or more of the screening tests. The automated test detected many more Reiter positive sera (127) than the manual test (83). Conversely, fewer CWR positive sera were detected by the automated test (60) than by the manual test (82). There was little difference between the number of positive sera detected by the ART (73) and the VDRL slide test (71). In 19 instances the automated tests detected positive sera which registered as completely negative in the manual tests, and four seropositive cases which the automated tests had failed to detect were detected by the manual tests, and four seropositive cases which the automated tests had failed to detect were detected by the manual tests. It was concluded that a combination of the ART and automated Reiter protein complement fixation test (ARPCFT) would be ideal for use in a large-scale screening programme for the detection of syphilis.     

Evaluation of the Vitek-2 extended-spectrum β-lactamase test against non-duplicate strains of Enterobacteriaceae producing a broad diversity of well-characterised β-lactamases

The Vitek-2 extended-spectrum β-lactamase (ESBL) test was assessed using a collection of 94 ESBL-positive and 71 ESBL-negative non-duplicate isolates of Enterobacteriaceae. These isolates produced a wide diversity of well-characterised β-lactamases, including 61 different ESBLs, two class A carbapenemases and various species-specific β-lactamases. ESBL detection was performed using (i) the conventional synergy test as recommended by the Comité de l'Antibiogramme de la Société Française de Microbiologie, (ii) the CLSI phenotypic confirmatory test for ESBLs, and (iii) the Vitek-2 ESBL test. For Escherichia coli and klebsiellae, the sensitivity/specificity values were 97.3%/96.9% for the synergy test, 91.8%/100% for the CLSI phenotypic confirmatory test, and 91.8%/100% for the Vitek-2 ESBL test. For other organisms, the sensitivity/specificity values were 100%/97.4% for the synergy test, 90.5%/100% for the CLSI phenotypic confirmatory test, and 90.5%/100% for the Vitek-2 ESBL test. The Vitek-2 ESBL test seemed to be an efficient method for routine detection of ESBL-producing isolates of Enterobacteriaceae, including isolates producing AmpC-type enzymes.     

Detection of toxoplasmosis by agglutination of parasites. Value of a very sensitive antigen in the search for specific immunoglobulins G

A method that increases the sensitivity and specificity of the direct agglutination (AG) test for diagnosis of infection with Toxoplasma gondii is described. Qualitative results in the Sabin-Feldman dye test (DT) and AG test were in excellent agreement (98%). Differences in titers between these two tests often related to the length of time the individual was infected. The AG titer is most often lower than the DT titer during acute (recent) infection; the AG test titer is most often higher than the DT titer in older or chronic infection. If the AG test antigen described here can be made available, the AG test would be ideal for use as a screening test and would provide a simple and inexpensive means for the surveillance of seronegative women during pregnancy and for detection of seroconversions.     

Detection of neutrophilocytes and NO2-producing bacteria in urine by dipstick BM-test-9

A prospective study compared the detection of leucocytes and bacteria in urine with the dipstick test (presence of esterases in granulocytes and nitrite) to chamber counting of urine, microscopic examination of the urinary sediment, and urine culture. Examined were 174 urine specimens. The dipstick esterase test and the sediment count were almost equally sensitive in detecting leucocyturia. Using chamber count and a cut-off point of 10 or more leucocytes per cubic millimeter as denoting significant leucocyturia, the esterase test gave a predictive value for negative test (PV neg) of 75% and a predictive value for positive test (PV pos) of 96%. PV neg of the dipstick nitrite test was 78% and PV pos 100% in detecting bacteriuria (10(5) bacteria per milliliter). Combining the esterase test with the nitrite test did not increase PV neg. Our result was that the dipstick test seems to be a simple screening procedure for leucocyturia and bacteriuria. The test is suggested to replace the time-consuming microscopic examinations of urine for leucocytes. When the nitrite test is positive, routine urine culture may be omitted.     

Retrospective analysis of the results of acellular pertussis vaccine toxicity tests performed in Korea

Specific toxicity test is a major quality control test for acellular pertussis (aP) vaccines performed by manufacturers and regulatory authorities. The 'mouse body weight gain test (MWGT)', the 'leukocytosis-promoting test (LPT)' and the 'histamine sensitization test (HIST)' have been conducted to check the specific toxicity of all batches of aP vaccines used in Korea through the national quality control program, which requires a lot of animals, labor and time. In this study, test results obtained in the past 9 y from a total of 258 lots of aP vaccines were examined retrospectively to evaluate the three test methods. A pairwise comparison of the test results indicated a good correlation between LPT and HIST, whereas MWGT showed no correlation with either LPT or HIST. Moreover, the reversion to toxicity was higher than the residual toxicity in the majority of lots tested by HIST, which indicated that the histamine-sensitizing toxicity, although rated within a safe range, increased during the vaccine storage. Thus, the vaccine safety test results accumulated in the past might be useful for the improvement of test protocols.     

Rapid diagnosis of rotavirus gastroenteritis by a commercial latex agglutination test.

The Rotalex test, a commercial latex agglutination test for rotavirus, was compared with direct electron microscopy (EM) and the Rotazyme test I, a commercial enzyme immunoassay, for detection of rotavirus in stools of children and neonates. For initial stool specimens from 265 children (less than 3 years old) with diarrhea, the Rotalex test had a sensitivity of 81.7% and specificity of 99.5% compared with EM results. Positive and negative predictive values were 98 and 94.9%, respectively. The Rotalex test was slightly more sensitive and specific than the Rotazyme test. When daily stool specimens from patients with rotavirus gastroenteritis were examined, the sensitivity of the Rotalex test varied depending on the time of stool collection relative to the onset of symptoms. Sensitivity was 100 (20/20), 96 (23/24), and 54% (7/13) during 1 to 4, 5 to 7, and 8 to 18 days, respectively, after the onset of symptoms. The sensitivity of the Rotazyme test varied similarly with days from onset. We also examined 214 EM-negative stool specimens from asymptomatic newborns. False positivity by the Rotalex test was only 3.3% (7/214) compared with 4.2% (9/215) for the Rotazyme test. The Rotalex test was as sensitive and specific as EM for detection of rotavirus during the acute stage of illness and much faster and cheaper than EM or the Rotazyme test. The test appears to be suitable for routine use in small hospitals, emergency wards, or even the physician's office for rapid diagnosis of rotavirus gastroenteritis.     

Visuwell Reagin, a non-treponemal enzyme-linked immunosorbent assay for the serodiagnosis of syphilis.

A urease-based enzyme-linked immunosorbent assay (ELISA) has been developed for the detection of reagin antibodies in serum. Visuwell Reagin (ADI Diagnostics Inc., Rexdale, Ontario, Canada) is a non-treponemal screening test for the serodiagnosis of syphilis which has the benefits of large batch testing, automatability, and objective interpretation of results. Unheated, undiluted sera are incubated in 96-well microtiter plates coated with a modified cardiolipin-lecithin-cholesterol antigen. Antibody bound to the plate is detected by an anti-human immunoglobulin G-urease conjugate. The procedure consists of three steps, with a total test time of 60 min. Visuwell Reagin ELISA was compared with the Venereal Disease Research Laboratory (VDRL) test and the reagin screening test (RST) with the following results. For ELISA versus the VDRL test, the sensitivities for untreated syphilis (n = 37) were 97.3% for both ELISA and the VDRL test, the confirmatory positive values (n = 79) were 84.8% for ELISA and 72.2% for the VDRL test, and the specificities for normal samples (n = 1,327) were 98.8% for ELISA and 99.5% for the VDRL test. For ELISA versus RST, the sensitivities for untreated syphilis (n = 57) were 94.7% for ELISA and 87.7% for RST, the confirmatory positive values (n = 26) were 96.2% for ELISA and 92.3% for RST, and the specificities for normal samples (n = 1,891) were 99.6% for ELISA and 99.3% for RST. The overall concordance values of ELISA with VDRL test and RST were 96.7 and 97.9%, respectively. The specificity of ELISA compared with that of RST may be underestimated, since confirmatory data were not available for all apparent false-positive samples. Visuwell Reagin had increased sensitivity and similar specificity compared with flocculation tests.     

Comparison of Affirm VPIII and Papanicolaou tests in the detection of infectious vaginitis

To compare the Affirm VPIII molecular test (Becton Dickinson, Burlington, NC) with morphologic identification used in routine Papanicolaou (Pap) test screening in the detection and identification of Candida species, Trichomonas vaginalis, and Gardnerella vaginalis, we identified 431 cases with a concomitant Pap test and Affirm VPIII assay performed from the archives of a large academic institution. The study population consisted of women ranging in age from 17 to 79 years (mean and median ages, 33 and 31 years, respectively). With a routine Pap test, 60 patients (13.9%) were found to have bacterial vaginosis, 60 (13.9%) candidiasis, and 3 (0.7%) Trichomonas infection. With the Affirm VPIII assay, 183 (42.5%) patients tested positive for G vaginalis, 70 (16.2%) positive for Candida species, and 10 (2.3%) positive for T vaginalis. The differences were statistically significant. The results demonstrate that our patient population had a high incidence of bacterial vaginosis/Candida vaginitis; however, the Affirm VPIII was a more sensitive diagnostic test for the detection and identification of all 3 organisms compared with the Pap test.     

Comparison of screening methods for detection of extended-spectrum beta-lactamases and their prevalence among Escherichia coli and Klebsiella species in Hong Kong

Three tests, the disk diffusion test, the double-disc synergy test and the inhibitor-potentiated disc diffusion test, were compared for their abilities to detect production of extended-spectrum beta-lactamases (ESBL) in 702 Escherichia coli and 472 Klebsiella spp. strains from four hospitals. Eleven percent E. coli and 13% Klebsiella spp. were found to produce ESBL. As an indicator of ESBL activity, the sensitivities of the five extended-spectrum beta-lactams were as follows: cefotaxime (100%), cefpodoxime (99.3%), ceftriaxone (98.6%), aztreonam (93%) and ceftazidime (57.7%) when interpreted using the National Committee for Clinical Laboratory Standards criteria. Their positive predictive values ranged from 67.8-83.8%. Both the inhibitor-potentiated disc diffusion test and the double-disc synergy test (at three inter-disc widths of 20, 25 and 30 mm) were capable of identifying all the ESBL-producers. However, at a single inter-disc width of 30 mm, the double-disc synergy test has limited sensitivity (83.8%). As a second test for confirming ESBL activity in strains with reduced susceptibility to beta-lactams, the inhibitor-potentiated disc diffusion test is therefore a simple and reliable option.     

Comparison of the maintenance of wakefulness test (MWT) to a modified behavioral test (OSLER) in the evaluation of daytime sleepiness

The objectives were to evaluate the correlation between sleep onset as defined by the Oxford sleep resistance (OSLER) test and by simultaneous electroencephalography (EEG) and to determine the correlation between sleep latencies measured by the OSLER test and maintenance of wakefulness test (MWT) performed on the same day. This was a prospective, cross-sectional study carried out in a tertiary-care university-based sleep laboratory. Participants were 11 consecutive subjects presenting to the sleep center with clinical indications for nocturnal polysomnography and MWT. The interventions included MWT and OSLER test. Mean sleep latencies for the OSLER and MWT in each subject were closely correlated (ICC = 0.94, [Intra-class correlation]P < 0.05). Sleep latency by OSLER and simultaneous measurement of EEG also had excellent agreement (ICC = 0.91) with a bias of -0.97 min. The OSLER test is a practical and reliable tool for evaluating daytime sleepiness when compared with the MWT. No obvious systematic adaptation was seen during sequential OSLER test performance. Given its portability and minimal technical requirements, the OSLER test may be useful for large-scale applications in the evaluation of daytime wakefulness and vigilance.     

Clinical significance of a borderline titer in a negative ELISA test for heparin-induced thrombocytopenia

We studied the usefulness of repeated enzyme-linked immunosorbent assay testing for heparin-induced thrombocytopenia (HIT) when the initial test result was negative and sought to determine whether the titer of the initial negative result correlated with the likelihood of obtaining a positive test result in repeated testing. We divided 150 patients who underwent HIT testing into 3 groups (50 patients each): (1) very low titer negative (0.0%-33.3% of the threshold for a positive test); (2) low titer negative (33.4%-66.6% of the threshold); and (3) high titer negative (66.7%-99.9% of the threshold). Among the patients who underwent a repeat test, 5% (1/20) of group 1 patients, 13% (4/32) of group 2 patients, and 43% (13/30) of group 3 patients tested positive in the repeat test (P = .0026). Thus, nearly half of patients with initially negative HIT test results had positive results in the repeat test if the negative titer was 66.7% or more of the threshold. If laboratories report the HIT titer, rather than just negative or positive, the titer might help clinicians predict which patients have HIT despite a negative initial test, and the overall sensitivity for diagnosing HIT might be improved.     

Direct agglutination test for diagnosis of Toxoplasma infection: method for increasing sensitivity and specificity.

A method that increases the sensitivity and specificity of the direct agglutination (AG) test for diagnosis of Toxoplasma gondii infection is described. Qualitative results in the Sabin-Feldman dye test (DT) and AG test were in excellent agreement (98%). Differences in titers between these two tests often related to the length of time the individual was infected. The AG test titer was most often lower than the DT titer during acute (recent) infection; the AG test titer was most often higher than the DT titer in older or chronic infection. If the AG test antigen described here can be made available, the AG test would be ideal for use as a screening test and would provide a simple and inexpensive means for the surveillance of seronegative women during pregnancy and for detection of seroconversions.     

Comparison of the Serodia Treponema pallidum particle agglutination, Captia Syphilis-G, and SpiroTek Reagin II tests with standard test techniques for diagnosis of syphilis

We compared the microhemagglutination assay for Treponema pallidum (MHA-TP), a treponemal test, with two other treponemal tests, the Serodia Treponema pallidum particle agglutination (TP-PA) assay and the Captia Syphilis-G enzyme immunoassay, using 390 clinical serum samples. We also compared two nontreponemal tests, the rapid plasma Reagin (RPR) card test and the SpiroTek Reagin II test. Agreements of the MHA-TP with the TP-PA test and the Syphilis-G test were 97.4 and 97.7%, respectively. There was 89.2% agreement between the RPR and Reagin II tests. The Reagin II test was more apt to be reactive if the treponemal test was also reactive. We conclude that either the Serodia TP-PA test or the Captia Syphilis-G test is an appropriate substitute for the MHA-TP and that the Spirotek Reagin II test could substitute for the RPR test as a screening test.     

An alternative linear trend analysis for assessing the results of the mouse lymphoma assay

As recommended by the mouse lymphoma assay (MLA) Workgroup of the International Workshop on Genotoxicity Testing (Aberdeen, 2003), a trend test is critical if an induced mutant frequency (MF) of at least 126 × 10(-6) (global evaluation factor, GEF) is achieved at one or more test concentrations. Only those responses that both achieve the GEF and a significant trend are biologically relevant. While no specific trend test was recommended by the Workshop, a trend test was recommended by the UK Environmental Mutagen Society (1989). The test uses MF (untransformed) averaged over replicate cultures following a consistency test (against a historical heterogeneity factor) in a weighted linear regression with chi-square (χ(2)) test for slope and returns significant results in virtually all cases that are positive for the GEF, including those with no apparent dose-response. We have explored an alternative method where the natural logarithm of MF and its variance are estimated for each replicate culture separately and used in a weighted ordinary linear regression with t-test for slope. Using test cases positive for the GEF, the P-value from this model is shown to be sensitive to changes in the number of replicates, the shape and magnitude of mutant induction, in contrast to the χ(2) model. Cases with no apparent dose-response and thereby questionable biological significance are tested negative by our method but positive by the χ(2) model. Our method is thus straight-forward and provides a meaningful complement to the GEF in assessing the biological significance of the MLA results.     

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.     

Development and application of immunochromatographic tests for the detection of staphylococcal enterotoxin E

Two rapid immunochromatographic assay formats for the detection of Staphylococcus aureus enterotoxin serotype E (SEE) were developed. For both tests, polyclonal antibodies against SEE were immobilized on a membrane strip representing the test zone, while second anti‐SEE antibodies conjugated to dyed latex particles were employed as markers in sandwich immunoassay. In a two‐step test format, sample and labelled antibodies were preincubated prior to immunochromatography, whereas in a one‐step test the labelled antibodies were integrated in the test pad and activated by addition of the sample solution. In the presence of SEE in a sample solution, colour development at the antibody‐coated zone occured within 20 min. The visual detection limits for SEE in buffer solution were at 5 ng ml^?1 (two‐step test) and at 10 ng ml^?1 (one‐step test), respectively. Both assays were specific for SEE and showed no cross‐reaction with serotype A, B, C, and D enterotoxins. When the two‐step test format was used for the identification of SEE in S. aureus culture broth, the detection limit was found to be 10 ng ml^?1. Culture supernatants of 10 enterotoxigenic strains of S. aureus were analysed with the immunochromatographic two‐step test and with a microtitre plate enzyme immunoassay (EIA) test kit for enterotoxins A‐E. Results obtained by the immunochromatographic test (presence or absence of SEE) were in excellent agreement with those of the microtitre EIA.     

Performance characteristics and utilization of rapid antigen test,DNA probe,and culture for detection of group a streptococci in an acute care clinic

Group A streptococcus (GAS) antigen testing has become a routine point-of-care (POC) test in acute care settings. Concern about performance parameters (PP) of these tests as well as inappropriate antibiotic use has resulted in various recommendations regarding diagnosis of GAS. There were two objectives in this study. The first was to evaluate the rapid GAS antigen test presently in use (Thermo BioStar, Boulder, Colo.) and the GAS Direct probe test (Gen-Probe, San Diego, Calif.) compared to culture. The second was to define the optimal use of these technologies in a large acute care pediatric clinic. A total of 520 consecutive pediatric patients presenting with symptoms of pharyngitis at any of three Lahey Clinic acute care facilities were evaluated. Pharyngeal specimens were collected using a double-swab collection device (Copan, Corona, Calif.). One swab was used for the antigen test, the second was used for the probe test, and the pledget was placed in the collection device for culture on 5% sheep blood agar, incubated for 48 h anaerobically, and subsequently placed in Todd-Hewitt broth. After discrepant analysis, sensitivity, specificity, and positive and negative predictive values were as follows: 94.8, 100, 100, and 96.9% for the probe test and 86.1, 97.1, 93.7, and 93.4% for the antigen test, respectively. Sensitivity using an enhanced culture technique was 99.4% (163 of 164). False-positive (FP) antigen results were often seen from patients previously diagnosed and/or treated for GAS. No FP results were seen with the probe test. Colony counts for the false-negative (FN) antigen tests were higher than those for the FN probe tests. Compared to culture and DNA probe, the rapid antigen test (RAT) offered a result at the time of the patient's visit, with acceptable PP when prevalence of disease is high. Follow-up testing with the RAT of GAS patients who previously tested as positive should be avoided due to increased FP results. The probe test was comparable to culture in performance. Results indicate the probe test can be used as the primary test or as a backup to negative antigen tests. The probe test offers the advantage over culture of same-day reporting of a final result but, in contrast to a POC test, necessitates follow-up communication to the patient. Preliminary data show the specificity of the probe test to be greater than that of the RAT for patients previously diagnosed with GAS.     

Evaluation of a Rapid Immunochromatographic Test for Diagnosis of Dengue Virus Infection

A rapid (<7-min) immunochromatographic test for immunoglobulin M (IgM) and IgG antibodies to dengue viruses was evaluated by using hospital admission and discharge sera from 124 patients. The reference laboratory diagnosis was based on the results of virus isolation, hemagglutination-inhibition assay (HAI), and enzyme immunoassay (EIA). By the standard assays, patients experienced primary dengue virus infection (n = 30), secondary dengue virus infection (n = 48), Japanese encephalitis (JE) virus infection (n = 20), or no flavivirus infection (n = 26). The rapid test demonstrated 100% sensitivity in the diagnosis of dengue virus infection and was able to distinguish between primary and secondary dengue virus infections through the separate determinations of IgM and IgG. For all patients with primary dengue virus infection a positive test for IgM to dengue virus and a negative test for IgG to dengue virus were obtained, whereas for 46 of 48 patients (96%) with secondary dengue virus infection, a positive test for IgG to dengue virus with or without a positive test for IgM to dengue virus was obtained. The remaining two patients with secondary dengue virus infection had positive IgM test results and negative IgG test results. Furthermore, the rapid test was positive for patients confirmed to be infected with different dengue virus serotypes (12 infected with dengue virus serotype 1, 4 infected with dengue virus serotype 2, 3 infected with dengue virus serotype 3, and 2 infected with dengue virus serotype 4). The specificity of the test for nonflavivirus infections was 88% (3 of 26 positive), while for JE virus infections the specificity of the test was only 50% (10 of 20). However, most patients with secondary dengue virus infection were positive for both IgM and IgG antibodies to dengue virus, while no patients with JE virus infection had this profile, so cross-reactivity was only a concern for a small proportion of patients with secondary dengue infections. The rapid test demonstrated a good correlation with the reference EIA and HAI and should be useful for the rapid diagnosis of dengue virus infections.