Rapid immunoperoxidase assay for detection of respiratory syncytial virus in nasopharyngeal secretions

Stability of respiratory syncytial virus antigen due to buffer treatment for direct detection in nasopharyngeal specimens with enzyme immunoassay

We developed an enzyme immunoassay (direct EIA; Enzygnost RSV[Ag]) for the direct detection of respiratory syncytial virus (RSV) antigen in nasopharyngeal specimens (NPS). The test procedure is the same as our recently described direct EIA for detection of influenza A and B virus antigens in NPS. For practical purposes it is of advantage to differentiate respiratory viruses on the same microtitration plate in the same run. The test shows no limitations by sample consistency, and results are obtained within 4 hr. In contrast to other test systems, sonification is not necessary. This is due to the sample buffer STD. We studied the influence of sample buffer STD on the stability of RSV (strain Long) antigen at different temperatures over a period of 7 days. PBS-BSA-buffer served as control. The treatment and storage of RSV (strain Long) with sample buffer STD at room temperature or at 4 degrees C showed no decrease of antigen detectability. The antigen is very stable in contrast to the storage of RSV (strain Long) in PBS-BSA buffer during the observation period of 7 days. Consequently, when NPS are stored in sample buffer STD, results of direct EIA are independent from the time of transport and temperature within 7 days. Thirty-eight NPS from infants with confirmed RSV infection were investigated. Confirmation was performed by virus isolation (n = 29) or with commercially available enzyme immunoassays or immunofluorescence test (n = 9). The direct EIA showed a specificity of 99.3% (n = 140) and a sensitivity of 95% (n = 38).

Application of immunoassay of encephalomyocarditis virus in cell culture with enzyme-labeled virus-specific monoclonal antibodies for rapid detection of virus, neutralizing antibodies, and interferon

Encephalomyocarditis virus (EMCV)-specific monoclonal antibody UM 21.1 labeled with horseradish peroxidase was used to detect EMCV in L-cell monolayers. This direct enzyme immunoassay of EMCV, performed in wells of 96-well plates, could be applied for various purposes, such as early detection of virus multiplication, determination of 50% tissue culture infective doses, and rapid titration of interferon and EMCV-neutralizing antibodies. Multiplication of EMCV is indicated by a rapid increase of the absorbance values measured against EMCV-infected L cells starting as early as 4.5 h after virus inoculation. The early rise of absorbance (i.e., virus multiplication) is inhibited by interferon, allowing its rapid titration. Preincubation of the virus inoculum with neutralizing antibodies also yielded decreased absorbance values. With the latter enzyme immunoassay for neutralizing antibodies, performed after an infection period of 8 h, antibody titers measured were comparable to those obtained with a conventional plaque reduction test. We assume that similar assays could be developed for other picornaviruses (e.g., polioviruses).

Enzyme immunoassay of mumps virus in cell culture with peroxidase-labelled virus specific monoclonal antibodies and its application for determination of antibodies

Mumps neutralizing monoclonal antibodies (MAs) were purified and labelled with horseradish peroxidase and used to detect virus-infected Vero cells, which were seeded as monolayers in wells of 96-well plates. This direct enzyme immunoassay (EIA) in cell culture proved to be a sensitive method for detection and titration of mumps virus and it may be useful for diagnostic purposes. The EIA is also suitable for the rapid determination of neutralizing antibodies. Neutralization of mumps virus by preincubation with either monoclonal or polyclonal antibodies was indicated by inhibition of the absorbance at 450 nm as measured with a multichannelled photometer. The EIA (duration 2 days) for determination of mumps neutralizing antibodies is an attractive alternative for the plaque reduction test (duration 6 days).

Detection of respiratory syncytial virus in clinical specimens by viral culture, direct and indirect immunofluorescence, and enzyme immunoassay

We evaluated prospectively the detection of respiratory syncytial virus (RSV) by culture and by direct antigen detection using an indirect immunofluorescence assay (IFA), a direct monoclonal immunofluorescence assay (DFA), and a monoclonal enzyme immunoassay (EIA). Of 221 specimens, 95 (43%) were culture positive for RSV, 4 (1.8%) contained more than one virus, and 17 (7.6%) contained a virus other than RSV. Overall, HEp-2 and Flow 6000 cells grew significantly more RSV isolates (82 and 72%, respectively) than A549 cells, which grew only 29% of the isolates. The mean time for RSV detection with HEp-2 cells was 2.9 days. This was significantly less than the mean time for RSV detection with either Flow 6000 cells (6.1 days) or A549 cells (6.4 days). Of 221 specimens, 129 were tested simultaneously by culture, IFA, and DFA. Of these 129 specimens, 62 (48%) were positive by culture, 69 (53%) were positive by IFA, and 70 (54%) were positive by DFA. For 92 specimens screened simultaneously by culture, IFA, and EIA, positive results were obtained for 33 (36%) of the specimens by both culture and IFA and for 29 (32%) of the specimens by EIA. Of 126 culture-negative specimens, 21 (17%) were positive for RSV when determined by IFA. Conversely, 14 (15%) of 95 RSV culture-positive specimens were negative by IFA, whereas DFA missed 19% of the culture-positive specimens. Compared with culture, the Kallestad EIA kit had a sensitivity and specificity of 73 and 92% respectively, but missed 9 (27%) of 33 culture-positive specimens. These data demonstrate that isolation by culture continues to be important for viral diagnosis of REV infections and that for valid comparative studies between viral isolations and rapid detection methods, both sensitive host cells and appropriate test conditions are required.

Peroxidase-antiperoxidase assay for rapid detection of respiratory syncytial virus in nasal epithelial specimens from infants and children

A peroxidase-antiperoxidase (PAP) assay for the rapid detection of respiratory syncytial virus was compared with the indirect immunofluorescence method and with viral culture. Nasal epithelial specimens from 147 infants and children with acute respiratory infections were obtained and evaluated for the presence of respiratory syncytial virus antigens. Sensitivity, specificity, and accuracy by PAP were 91.7, 84.8, and 87.1%, respectively, and 87.0, 88.5, and 88.0%, respectively, by immunofluorescence compared with viral culture. The PAP assay was found to be as accurate as the indirect immunofluorescence method and more convenient to perform, since the color reaction and cell morphology were more easily observable by light microscopy. A new specimen collection method is reported; gentle scraping of the superficial nasal mucosa by the Rhino-probe method provided sufficient numbers of epithelial cells to perform multiple assays.

Capture-ELISA for serum IgM antibody to respiratory syncytial virus

A four-component solid-phase capture enzyme immunoassay was set up to test for serum IgM antibody to respiratory syncytial (RS) virus and was compared with immunofluorescence assay (IFA). A total of 128 young children with acute respiratory infections were studied. Thirty-six were shown to be RS virus-positive by the detection of RS virus in nasopharyngeal secretions and 92 were RS virus-negative. A serum specimen was collected after admission to the hospital (days 0-4) and a further specimen was obtained during days 10-14. Out of 36 RS virus-positive patients, 28 (77.7%) were found to be positive for IgM by both capture-ELISA and IFA. Out of 92 RS virus-negative patients 5 (5.4%) were IgM-positive. Four false-positive results were obtained by IFA due to the presence of rheumatoid factor. The capture-ELISA was shown to be a reliable technique in detecting specific IgM antibody to RS virus.

Rapid detection of respiratory syncytial virus in nasopharyngeal secretions by enzyme-linked immunosorbent assay

A new enzyme-linked immunosorbent assay (ELISA) respiratory syncytial virus antigen detection kit (Ortho Diagnostics, Inc., Raritan, N.J.) was compared with virus culture and with the indirect fluorescent antibody test (FAT) by using fresh nasal washings from children with suspected respiratory syncytial virus infection. Both uncentrifuged nasal washings and pellets from centrifuged split specimens were examined by ELISA. The ELISA was considered positive when the optical density was greater than the mean background optical density plus 0.15. Specimens positive by ELISA but negative by culture and FAT were reexamined in an ELISA blocking assay. Of 337 uncentrifuged specimens, 124 (37%) were positive by culture, 107 (32%) were positive by FAT, and 166 (49%) were positive by ELISA. Blocking assays showed that 21 of 30 (70%) of the seemingly false-positive ELISA tests were, in fact, true-positives and that the cultures and FATs were falsely negative. A patient specimen was considered positive when it was positive by virus culture, FAT, or blocking assay. The sensitivity, specificity, and positive predictive value of the ELISA test were 88, 94, and 95%, respectively. Centrifugation of nasal washings raised the sensitivity from 88 to 92% but reduced the specificity from 94 to 81%. We conclude that the Ortho ELISA test of uncentrifuged nasal washings is more sensitive than virus culture or indirect FAT and is highly specific.

Rapid diagnosis of viral infections with fluorescent antisera

Viral immunofluorescence tests were performed with commercial antisera on 1046 specimens of respiratory, conjunctival corneal and dermal origin to compare the diagnostic effectiveness of direct examination by immunofluorescence with culture. The fluorescence assays were found to be highly sensitive for respiratory syncytial and measles virus in nasopharyngeal aspirates from children, but less satisfactory for other respiratory viruses. The test detected 38% of the adenovirus positives from conjunctival specimens and 67% of the combined herpes simplex virus positives from the latter 3 groups. Despite the reduced sensitivity of fluorescence for some viruses, a case is presented for more widespread use of fluorescence in routine microbiology laboratories because of its simplicity, speed and cost-effectiveness compared with culture which is labour-intensive and time consuming.

Detection of Semliki Forest virus in cell culture by use of an enzyme immunoassay with peroxidase-labeled monoclonal antibodies specific for glycoproteins E1 and E2

Four noncompeting monoclonal antibodies (MA) directed against either the E1 (UM 8.64 and 8.139) or E2 (UM 8.55 and 8.73) glycoprotein of Semliki Forest virus were purified and labeled with horseradish peroxidase. Each enzyme-labeled MA was tested alone and in combination with others for its sensitivity to detect virus-infected cells. Semliki Forest virus-infected L cells seeded as monolayers in 96-well plates were screened for the virus after incubation with enzyme-labeled MA and a substrate. In this system single enzyme-labeled MA even at high dilution (10(3.0) to 10(4.5] were able to detect virus-infected cells. The sensitivity of the test could be enhanced by combining two noncompeting MA (10(4.5) to 10(5.0]. Combinations of three and four MA were less effective, due to high absorbance values for noninfected cells. The threshold of virus defection was between 10(5) and 10(6) PFU/ml. This test is sensitive and specific and therefore may be useful for diagnostic purposes.

An immunoperoxidase assay for the detection of specific IgA antibody in Epstein-Barr virus infections

A technique using indirect immunoperoxidase antibody was developed for the detection of specific serum IgA antibody to Epstein-Barr virus capsid antigen and early antigen. The IgA technique was compared with an immunofluorescence antibody method. Epstein-Barr virus IgA antibody against viral capsid antigen was detected in all nine patients with Epstein-Barr virus associated undifferentiated nasopharyngeal carcinoma, in 13 (72.2%) of 18 patients with infectious mononucleosis, in 21 (28.3%) of 74 patients with acute lymphoblastic leukaemia, and in six (20%) of 30 patients who had recently had kidney transplants. Epstein-Barr virus IgA antibody against viral capsid antigen was also detected in four (10%) of 40 healthy subjects, but it was not found in any of 20 cord blood samples. Epstein-Barr virus IgA antibody to early antigen was detected in six (66.6%) patients with nasopharyngeal carcinoma and in two (2.7%) patients with acute lymphoblastic leukaemia. The immunoperoxidase assay for Epstein-Barr virus specific IgA was simple, reliable, and rapid and correlated well (r = 0.94) with the immunofluorescence antibody technique.