Ryan J. Welch

An evaluation of two commercially available ELISAs and one in-house reference laboratory ELISA for the determination of human anti-rabies virus antibodies.

The envelope glycoprotein G of rabies virus in vaccines induces the production of neutralizing antibodies important in the protection against the disease. The measurement of anti-envelope glycoprotein antibodies is a good predictor of the degree of humoral immunity in people during anti-rabies treatment or after vaccination. Several assays exist for the serological determination of antibody protection against rabies virus infection. Antibody neutralization by the rapid fluorescent focus inhibition test (RFFIT) or the fluorescent antibody virus neutralization (FAVN) test is currently the gold standard. Performance of the highly complex RFFIT and FAVN tests, however, requires specialized reference laboratories with expertise with this assay. Although not widely used, ELISA test kits are available and may be an additional option for testing that is more accessible. The aim of the present study was to evaluate available ELISA assays for the determination of anti-rabies antibodies. We compared the Bio-Rad Platelia Rabies II ELISA, DRG Rabies Virus IgG Ab ELISA and Focus Diagnostics Rabies Antibody Detection by ELISA to RFFIT. Bland-Altman plots comparing the Bio-Rad Platelia assay and the Focus Diagnostics assay to RFFIT showed a low degree of variability between the ELISA assays and RFFIT results except in samples with high RFFIT values. The agreement, sensitivity and specificity of Bio-Rad Platelia Rabies II ELISA when compared to RFFIT were 95.1 %, 94.1 % and 95.8 %, respectively. The DRG Rabies assay compared to RFFIT had an agreement of 77.7 %, a sensitivity of 86.7 % and a specificity of 69.4 %. The agreement, sensitivity and specificity of Focus Diagnostics Rabies Detection by ELISA when compared to RFFIT were 82.2 %, 91.7 % and 73.0 %, respectively. Overall, the Bio-Rad Platelia assay showed higher accuracy and specificity than either the DRG or Focus assays. All of these ELISAs, however, measure all antibody types and do not discriminate the neutralizing antibodies as measured by functional assays (RFFIT and FAVN) and cannot be relied upon to predict the neutralizing activity of the sera. The results of this study offer insight into the availability of alternative, less-complex methods to monitor rabies antibody titres in at-risk individuals following vaccination.

Assessment of Three Commercially Available Serologic Assays for Detection of Antibodies to Mycobacterium tuberculosis and Identification of Active Tuberculosis

ABSTRACT Tuberculosis (TB) caused by Mycobacterium tuberculosis remains a major world disease, with approximately 9 million new cases each year. Identification and treatment of active disease are essential for TB control. Serology may offer increased detection of active disease in patients with a positive tuberculin skin test (TST) or QuantiFERON-TB (QFT-G). The InBios Active TbDetect immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA), IBL M. tuberculosis IgG ELISA, and Anda Biologics TB ELISAs were evaluated for the ability to detect M. tuberculosis antibodies in patients with active disease. Agreement, sensitivity, and specificity for each ELISA were determined and compared to those for culture or amplified direct detection and M. tuberculosis low-risk control patients. The InBios Active TbDetect ELISA had an agreement of 96.2%, a sensitivity of 83.3%, and a specificity of 98.9%. The IBL M. tuberculosis ELISA had an agreement of 84.0%, a sensitivity of 5.6%, and a specificity of 100.0%. The agreement, sensitivity, and specificity of the Anda Biologics TB ELISA were 74.2%, 83.3%, and 72.0%, respectively. The sensitivity for detecting M. tuberculosis antibodies in human immunodeficiency virus-associated TB was 50% for both the InBios Active TbDetect ELISA and the Anda Biologics TB ELISA and 0% for the IBL M. tuberculosis ELISA. The positivity rates for InBios Active TbDetect ELISA, IBL M. tuberculosis ELISA, and Anda Biologics TB ELISA in latently infected individuals positive by TST and/or QFT-G were 5.1%, 0.0%, and 30.8%, respectively. It can be concluded that the InBios Active TbDetect IgG ELISA is superior to the other ELISAs in accurately detecting active TB.

Rapid immunochromatographic strip test for detection of anti-K39 immunoglobulin G antibodies for diagnosis of visceral leishmaniasis.

ABSTRACT InBios International has developed an immunochromatographic rapid strip for the detection of visceral leishmaniasis that requires minimal equipment and only a small amount of blood to run a test. We compared the InBios rapid strip test with the CDC immunofluorescent antibody assay, and the agreement, sensitivity, and specificity were 98%, 90%, and 100%, respectively.

Antituberculosis IgG Antibodies as a Marker of Active Mycobacterium tuberculosis Disease

ABSTRACT Anti-Mycobacterium tuberculosis IgG antibodies may aid in the diagnosis of active M. tuberculosis disease. We studied whether anti-M. tuberculosis IgG antibodies are elevated in active M. tuberculosis disease and assessed factors contributing to false-positive and -negative results. A retrospective study of 2,150 individuals tested by the QuantiFERON-TB Gold In-Tube (QFT-GIT) assay was conducted at the University of Utah, ARUP Laboratories, November 2008 to December 2010. All samples were tested with the InBios Active TbDetect antituberculosis (anti-TB) IgG antibody assay. Of 1,044 patients with a positive QFT-GIT, 59 (5.7%) were positive for M. tuberculosis antibodies. Fourteen of 1,106 (1.3%) with a negative or indeterminate QFT-GIT were positive for M. tuberculosis antibodies. M. tuberculosis antibody tests were positive in 61.5% with confirmed active M. tuberculosis disease and other mycobacterial infections. Over half of the false-negative M. tuberculosis antibody tests occurred in patients ≥90 years of age. False positives were seen in 12.9% of autoimmune patients. The odds ratio of being positive by the QFT-GIT and the InBios TB IgG assay increased with confirmed M. tuberculosis disease or highly suspected M. tuberculosis disease and was 86.7 (95% confidence interval [CI], 34.4 to 218.5) in these two groups compared to patients negative by both tests. Although anti-M. tuberculosis antibodies can be detected in patients with active M. tuberculosis disease, caution should be used with patients where immunoglobulin levels may be decreased or patients with autoantibodies.

Comparison of a Multiplexed Herpes Simplex Virus Type-Specific Immunoglobulin G Serology Assay to Immunoblot, Western Blot, and Enzyme-Linked Immunosorbent Assays

ABSTRACT The human herpes simplex virus (HSV) is highly pathogenic, with infections caused by two distinct antigenic types, HSV-1 and HSV-2. Differentiation of antibodies to these specific antigens can provide useful information for the diagnosis of subclinical or undiagnosed HSV-2 infections, as well as for reducing the risk of maternal transfer of HSV to the neonate. In this study, a multiplex assay capable of concurrent detection of HSV-1 and -2 immunoglobulin G (IgG) antibodies was compared to immunoblot, Western blot, and enzyme-linked immunosorbent assays. Agreement of the multiplex assay was 95% or greater (n = 332) for both HSV-1 and -2 compared to the three assays. Sensitivities for HSV-1 ranged from 94.9 to 97.9%, with specificities of 93 to 97%. For HSV-2, the sensitivity and specificity ranges were 92.6 to 98.9% and 98.3 to 98.7%, respectively. Our studies show that the multiplexed microsphere-based assay offers a sensitive and specific alternative method for the detection HSV-1 and -2 type-specific antibodies. Advantages of the multiplex assay include multiple results per assay, the inclusion of internal controls for each specimen, and higher throughput of results.

A comparison of Brucella IgG and IgM ELISA assays with agglutination methodology

Despite brucellosis having a low incidence rate in developed nations, it still remains the leading zoonotic disease in the world. Culturing of Brucella spp. provides good specificity but in cases where the fever is intermittent, sensitivity is problematic. This has led to the development of serological methods of detection. Brucella agglutination methods have been considered the serological gold‐standard since their inception, although commercial Brucella IgG and IgM enzyme‐linked immunosorbentassays are available to potentially aid in the diagnosis of the disease. In our study, anti‐Brucella IgG and IgM assays were compared with agglutination. Individually the IgG assay tested had an accuracy of 56% and the IgM assay had an accuracy of 77%. These poor accuracies reinforce Centers for Disease Controls conclusion that nonagglutination tests should not be used to confirm brucellosis. J. Clin. Lab. Anal. 24:160–162, 2010.

Evaluation of Two Immunoblot Assays and a Western Blot Assay for the Detection of Antisyphilis Immunoglobulin G Antibodies

ABSTRACT In the present study, two immunoglobulin G (IgG) immunoblot assays and one IgG Western blot assay were compared to the rapid plasma reagin test (RPR), the fluorescent treponemal antibody absorption test (FTA-ABS), and the Treponema pallidum particle agglutination assay (TP-PA). The agreement levels of the Viramed, Virotech, and MarDx assays were 97.0%, 96.4%, and 99.4%, and the agreements of samples inconclusive by FTA-ABS and resolved by TP-PA were 91.7%, 83.3%, and 69.4%, respectively.

Evaluation of a new commercial enzyme immunoassay for the detection of IgM antibodies to West Nile virus using a ratio method to eliminate nonspecific reactivity

As West Nile virus (WNV) has become endemic in the United States, following the first reported cases in New York during the summer of 1999, the demand for specific serology has increased. Several IgM capture ELISA assays for the detection of WNV‐specific IgM have been approved by the Food and Drug Administration for in vitro diagnostic testing, including kits from Focus Diagnostics and InBios International, Inc. The Focus Diagnostics IgM capture ELISA has a background subtraction protocol and the InBios IgM capture ELISA implements a ratio method to detect nonspecific reactivity due to rheumatoid factor, heterophile antibodies, and other interfering substances. We compared the InBios IgM capture ELISA with the Focus Diagnostics capture ELISA. Agreement, sensitivity, and specificity of the InBios IgM capture ELISA were 99, 98, and 100%, respectively. Samples that originally tested positive on the Focus Diagnostics IgM capture ELISA without the subtraction protocol and were then determined negative following the subtraction protocol agreed 100% with the InBios IgM capture ELISA. We conclude that a method to eliminate background reactivity is a necessary portion of any anti‐WNV IgM assay in order to eliminate false‐positive results. J. Clin. Lab. Anal. 22:362–366, 2008.

Correlation of Chlamydia and Chlamydophila spp. IgG and IgM antibodies by microimmunofluorescence with antigen detection methods

Correlation of serologic titers for Chlamydia trachomatis with other tests has been based on direct fluorescence antibody (DFA) testing and culture, but not on nucleic acid‐based tests that are used for screening. We retrospectively reviewed the specificity of antibodies against C. trachomatis, Chlamydia psittaci, and Chlamydophila pneumoniae by microimmunofluorescence (MIF) when compared with DFA, culture, nucleic acid probe, and transcription‐mediated amplification. Over a 6‐year period, 226 cases had both MIF and one of these other methods performed for comparison. Agreement between C. trachomatis antigen or nucleic acid detection and MIF results was 87% (197/226). C. trachomatis serology had a negative predictive value of 98%, and 10.6% of cases were positive by serology and negative by antigen testing. Of the 13 patients who had a positive C. trachomatis antigen or nucleic acid test result, 9 had IgG and/or IgM titers highest against C. trachomatis, 3 had IgG titers highest against C. pneumoniae, and 1 had undetectable titers for the three chlamydial species. Twenty‐five patients had positive IgG and/or IgM titers to C. trachomatis but negative antigen test results. Serologic testing can increase the sensitivity of detecting C. trachomatis infections. J. Clin. Lab. Anal. 25:305–308, 2011.

Seropositivity rates for measles, mumps, and rubella IgG and costs associated with testing and revaccination.

ABSTRACT Retrospective analysis of IgG test results and patterns for measles, mumps, and rubella revealed generally high seropositivity rates, with that of mumps being the lowest. A simplified cost analysis shows that when there is a suspicion of nonimmunity, serological testing may be cheaper than vaccination.