Enzyme immunoassay for direct detection of influenza type A and adenovirus antigens in clinical specimens

Developments in immunologic assays for respiratory viruses

In most hospitals, clinics, and doctor's offices, immunologic assays are the only tests performed on site for the diagnosis of respiratory viruses. More than other methods, immunoassays have been shown to affect patient management and save costs, aiding early administration of antiviral therapy, reduction in unnecessary tests and antibiotics, and earlier discharges. This article discusses the major immunologic methods employed for respiratory virus diagnosis, recent developments in immunoassays and sample collection, and current test algorithms.

Isolation and characterization of the thrombin-like enzyme from Cryptelytrops purpureomaculatus venom

A thrombin-like enzyme, purpurase, was purified from the Cryptelytrops purpureomaculatus (mangrove pit viper) venom using high performance ion-exchange and gel filtration chromatography. The purified sample (termed purpurase) yielded a homogeneous band in SDS-polyacrylamide gel electrophoresis with a molecular weight of 35,000. The N-terminal sequence of purpurase was determined to be VVGGDECNINDHRSLVRIF and is homologous to many other venom thrombin-like enzymes. Purpurase exhibits both arginine ester hydrolase and amidase activities. Kinetic studies using tripeptide chromogenic anilide substrates showed that purpurase is not fastidious towards its substrate. The clotting times of fibrinogen by purpurase were concentration dependent, with optimum clotting activity at 3mg fibronogen/mL. The clotting activity by purpurase was in the following decreasing order: cat fibrinogen>human fibrinogen>dog fibrinogen>goat fibrinogen>>rabbit fibrinogen. Reversed-phase HPLC analysis of the products of action of purpurase on bovine fibrinogen showed that only fibrinopeptide A was released. Indirect ELISA studies showed that anti-purpurase cross-reacted strongly with venoms of most crotalid venoms, indicating the snake venom thrombin-like enzymes generally possess similar epitopes. In the more specific double-sandwich ELISA, however, anti-purpurase cross-reacted only with venoms of certain species of the Trimeresurus complex, and the results support the recent proposed taxonomy changes concerning the Trimeresurus complex.

Monoclonal antibodies for the rapid diagnosis of influenza-B virus infections by ELISA: production and characterization

BACKGROUND

Monoclonal antibodies directed against conserved epitopes of viral proteins have substantially improved the accuracy of several immunochemical methods in diagnostic virology.

OBJECTIVES

To characterize mouse monoclonal antibodies directed against structural protein antigens of influenza-B virus and evaluate their use as diagnostic reagents for the direct detection of such antigens in clinical specimens from patients with respiratory infections of unknown aetiology.

STUDY DESIGN

(a) Production and characterization of monoclonal antibodies against influenza-B viral antigens, and (b) their use in two different ELISA systems for detecting influenza-B antigen either directly in clinical specimens or after confirmation by rapid culture in MDCK cells.

RESULTS

Four monoclonal antibodies were selected for their specificity for the nucleoprotein antigen as demonstrated by Western blot analysis. The specificity of these antibodies for different epitopes of the nucleoprotein was demonstrated by competition experiments, using unlabelled and biotin-labelled purified antibodies in a sandwich assay. All four antibodies belong to the mouse IgG(2a) isotype, lack haemagglutination inhibition and neutralization properties and exhibit titres as high as 10(-6) in ELISA with as little as 30 ng purified influenza-B virus. ELISA methods using these antibodies detected only influenza-B viral antigens in direct testing of clinical specimens from patients with known influenza-B or influenza-A infections, or after reisolating virus from such specimens in tissue culture of MDCK cells.

CONCLUSION

The antibodies were suitable for the direct detection and typing of influenza-B virus in clinical specimens or for use in rapid confirmation cultures.

Influenza

Influenza remains an important cause of morbidity and mortality in the United States. Although signs and symptoms of individual influenza cases are nonspecific, the epidemiology is characteristic, and a clinical diagnosis can be made accurately during epidemics. Several tests can be used to confirm influenza infection. Antiviral medications may be used for both treatment and prophylaxis, but prevention of influenza is most reliably achieved through vaccination.

Performance of virus isolation and Directigen Flu A to detect influenza A virus in experimental human infection

BACKGROUND

Few data exist to assess the sensitivity of different specimen types for viral detection during the course of influenza virus infection.

OBJECTIVES

This study assessed the relationships between quantitative influenza A virus replication and antigen detectability by the enzyme immunosorbent assay (EIA) Directigen Flu A in different type of samples during experimental human infection.

STUDY DESIGN

Fourteen volunteers were inoculated with influenza A virus A/Texas/36/91 (H1N1). Four specimens types were collected in sequence for quantitative isolation in cell culture and antigen testing from days 1 to 8 after inoculation.

RESULTS

Seventy-one (63%) of nasopharyngeal wash specimens were culture positive, compared to 51 (46%) of throat gargles, 51 (46%) of nasal swabs, and 27 (24%) of throat swabs. All subjects shed virus in their nasopharyngeal wash at least one day and 86% of subjects had a positive nasopharyngeal wash culture on day 2 after inoculation. The mean viral titers were highest on day 2 post inoculation for all specimen types and averaged 3.6 log10 TCID50/ml for nasal washes, 1.2 log10 TCID50/ml for throat gargles, 1.8 log10 TCID50/ml for the nasopharyngeal swabs, and 0.6 log10 TCID50/ml for the throat swabs. Mean viral titers in the nasal washes were significantly different (P<0.05) compared to other specimen types. The peak of sensitivity of EIA (compared to culture) was the second day after inoculation. Nasopharyngeal and throat swab results were combined for this analysis and considered positive by culture if positive in either or both samples. Thus, on day 2 the number of EIA positive samples relative to the number culture positive was 9/12 (75%) for nasopharyngeal wash specimens, 2/9 (22%) for throat gargles, and 7/11 (64%) for the combined throat and nasal swabs specimens.

CONCLUSIONS

Nasopharyngeal washes are the most sensitive sample type detecting influenza A virus in adults. For rapid diagnosis the Directigen Flu A is an alternative with a sensitivity compared to culture ranging between 64 and 78% if performed on nasopharyngeal specimens on day two or three after experimental infection in adults. However, if performed on other specimens or later in the course of infection the sensitivity is lower.

Typing and subtyping clinical isolates of influenza virus using reverse transcription-polymerase chain reaction

BACKGROUND

Influenza virus infections are a major cause of morbidity and the identification of the type or subtype of a clinical isolate has important clinical and epidemiological implications.

OBJECTIVES

To evaluate the ability of a reverse transcription-polymerase chain reaction (RT-PCR) assay to type and subtype clinical human isolates of influenza virus.

STUDY DESIGN

Reference strains of influenza A H1N1, A/H3N2, and B viruses and human clinical isolates of influenza virus representing antigenic variants from the last 15 years were evaluated using an RT-PCR assay.

RESULTS

Amplicons of 325, 198 and 365 base pairs in length were obtained from RNA extracted from influenza A/H1N1, A/H3N2 and B viruses, respectively. All human-derived A/H1N1, A/H3N2, and B reference strains and antigenic variants tested were correctly identified.

CONCLUSIONS

RT-PCR is an effective alternative to traditional methods for typing and subtyping influenza viruses.

An investigation on the antigenic cross-reactivity of Calloselasma rhodostoma (Malayan pit viper) venom hemorrhagin, thrombin-like enzyme and L-amino acid oxidase using enzyme-linked immunosorbent assay

Indirect ELISA shows that the antibodies to Calloselasma rhodostoma venom hemorrhagin (CR-HMG), thrombin-like enzyme (CR-TLE) and L-amino acid oxidase (CR-LAAO) exhibited strong to moderate cross-reactions with most crotalid and viperid venoms, but only anti-CR-LAAO cross-reacted with the elapid venoms. However, the indirect ELISA failed to detect some antigenic similarities demonstrable by cross-neutralization study. The double-sandwich ELISA for the three anti-C. rhodostoma venom components exhibited a much lower level of cross-reactions than the indirect ELISA.

Mixed viral infections: detection and management

An analysis was done of the incidence and nature of mixed virus infections diagnosed in the same clinical specimen from immunocompetent patients; respiratory viruses were emphasized. Few studies have addressed mixed viral infections in any systematic fashion. The relevant studies reviewed focused on clinical relationships or diagnostic methods. Data relating to multiple infections were usually derived incidentally to the purpose of the investigations. Sixty-three percent of the reports with data on mixed infections identified them in < 5% of the total number of viral infections. Respiratory syncytial virus was the most common coinfecting virus, and respiratory syncytial virus and influenza virus were the most common virus pair identified. In considering rapid diagnostic techniques, in 87% of the reports with available data a virus was diagnosed in > 10% of specimens that were negative for the virus targeted by one method. There was no indication that mixed infections were associated with increased disease in immunocompetent patients or in certain immunocompromised patients. Immunocompromised patients, however, appeared to have a greater incidence of multiple infections. Mixed infections of single cells also occur and may have important clinical implications relative to reactivation of latent viruses and enhanced disease. The requirement for a comprehensive strategy for viral diagnosis involving multiple techniques was indicated by these findings.

Diagnosis of equine influenza by the polymerase chain reaction

Influenza A is a common respiratory infection of horses, and rapid diagnosis is important for its detection and control. Sensitive detection of influenza currently requires viral culture and is not always feasible. The polymerase chain reaction (PCR) was used to detect DNA produced by reverse transcription of equine influenza in stored nasal secretions, vaccines, and allantoic fluids. Primers directed at a target of 212 bp on conserved segment 7 (matrix gene) of human influenza A/Bangkok/1/79(H3N2) produced amplification products of appropriate size with influenza A/Equine/Prague/1/56 (H7N7), A/Equine/Miami/63 (H3N8), A/Equine/Kentucky/79 (H3N8), and A/Equine/Kentucky/2/91 (H3N8) in infected frozen allantoic fluids and in frozen extracts of nasal swabs of 2 horses with naturally acquired influenza. The products bound a 32P-labeled hybridization probe to an inner region of the target. Control samples, including nasal secretions from a horse infected with herpesvirus, were negative. In a prospective study, 2 ponies inhaled aerosols of influenza A/Equine/Kentucky/2/91 (H3N8), and thereafter supernatants of nasal swabs in transport medium were obtained daily for 10 days for culture and PCR. Amplification products were evaluated by size and binding of a 32P-labeled probe and also by dot-blotting and binding of a biotin-labeled probe. Culture detected influenza more consistently than did PCR in the first 2 days of infection, but PCR detected virus more often later in infection. Gels were the most sensitive, but radiometric and biotin-labeled probes gave specific results and were consistently positive from days 3-6. PCR is suitable for detection of equine influenza in clinical samples.

An investigation into the antigenic cross-reactivity of Ophiophagus hannah (king cobra) venom neurotoxin, phospholipase A2, hemorrhagin and L-amino acid oxidase using enzyme-linked immunosorbent assay

The antigenic cross-reactivity of four Ophiophagus hannah (king cobra) venom components, the neurotoxin (OH-NTX), phospholipase A2 (OH-PLA2), hemorrhagin (OH-HMG) and L-amino acid oxidase (OH-LAAO) were examined by indirect and double sandwich ELISAs. The indirect ELISAs for OH-NTX, OH-PLA2 and OH-HMG were very specific when assayed against the various heterologous snake venoms and O. hannah venom components, at 25 ng/ml antigen level. At higher antigen concentrations (100-400 ng/ml), there were moderate to strong indirect ELISA cross-reactions between anti-O. hannah neurotoxin and venoms from various species of cobra as well as two short neurotoxins. However, anti-O. hannah hemorrhagin did not cross-react with any of the venoms tested, even at these high antigen concentrations, indicating that O. hannah hemorrhagin is antigenically very different from other venom hemorrhagins. Examination of the indirect ELISA cross-reactions between anti-O. hannah PLA2 and several elapid PLA2 enzymes suggests that the elapid PLA2 antigenic class has more than two subgroups. The antibodies to O. hannah L-amino acid oxidase, however, yielded indirect ELISA cross-reactions with many venoms as well as with OH-NTX, OH-PLA2 and OH-HMG, indicating that OH-LAAO shares common epitopes even with unrelated proteins. The double sandwich ELISAs for the four anti-O. hannah venom components, on the other hand, generally exhibited a higher degree of selectivity than the indirect ELISA procedure.

The use of enzyme-linked immunosorbent assay for the quantitation of Calloselasma rhodostoma (Malayan pit viper) venom and venom antibodies

The specificity and sensitivity of an indirect and two (an 'ordinary' and a 'rapid') double sandwich enzyme-linked immunosorbent assay (ELISA) procedures for the quantitation of Calloselasma rhodostoma (Malayan pit viper) venom were examined. The three assays were equally sensitive and the accuracy of the assays was not substantially affected by individual variation in the venom composition. The specificity of the assays was examined against 26 venoms from snakes of the families Viperidae and Elapidae. While the double sandwich ELISA procedures were sufficiently specific to be used in the clinical immunodiagnosis of C. rhodostoma bite in Malaysia, the indirect ELISA procedure exhibited extensive cross-reactivity with other Malaysian pit viper venoms. Attempts were made to improve the specificity of the indirect ELISA procedure for the quantitation of C. rhodostoma venom. A 'low ELISA cross-reactivity' venom fraction (termed VF52) was isolated from C. rhodostoma venom by repeated Sephadex G-100 gel filtration chromatography. The indirect ELISA procedure using antibodies to VF52 as immunoreagent showed an improvement in specificity. The use of the indirect ELISA procedure for the detection of C. rhodostoma antibodies was also examined and the results show that the assay was sufficiently specific to be used for retrospective diagnosis of C. rhodostoma bite in Malaysia, in particular when VF52 was used as the coating antigen.

Application of Directigen FLU-A for the detection of influenza A virus in human and nonhuman specimens

Directigen FLU-A, a new enzyme immunoassay membrane test, rapidly detects influenza A virus antigen in specimens from patients. Nasopharyngeal washes and pharyngeal gargles were used to determine the effectiveness of the assay as applied to different types of routinely collected clinical samples. All specimens had been previously shown to contain influenza A virus by virus isolation in tissue culture. Directigen FLU-A was 90% sensitive (95% confidence interval, 56 to 99.7%) with nasopharyngeal washes but only 39% sensitive (95% confidence interval, 17 to 64%) with pharyngeal gargles (P = 0.018) when used with samples containing similar amounts of infectious virus (50% tissue culture infective dose, 1.0 to 4.5). The intensity of the positive reaction with Directigen FLU-A did not correlate with the amount of virus in the specimens. Directigen FLU-A was found to detect cell-associated antigen more readily than free virus; only 20 infected cells were required to identify cell-associated influenza A virus antigen, whereas the limit of detection for free virus was 1.63 x 10(3) infectious virus particles. These findings suggest that Directigen FLU-A detects the cell-associated antigen present in clinical specimens rather than free virus. In addition, Directigen FLU-A detected avian and swine influenza A viruses in both cloacal swabs (75% sensitivity) and swine lung homogenates (86% sensitivity), indicating its potential usefulness in the surveillance of nonhuman influenza A viruses.

Pitfalls in determining IgG and IgG subclass antibodies to food antigens

Several variables were found to influence enzyme-linked immunosorbent assay (ELISA) measurements of IgG and IgG subclass antibodies to food antigens. Two polyclonal rabbit antibody reagents to human IgG, and two sets of murine monoclonal antibodies to human IgG subclasses, were compared as secondary reagents. The choice of both polyclonal and monoclonal reagents affected significantly the results. High levels of IgA to an antigen depressed the measurements of comparable total IgG antibodies but did not influence the percentages of the four IgG subclass activities. Different ways of expressing the IgG subclass results were compared and the validity of the reference measurements used to obtain them was examined. Information from previous studies, together with the present data, suggests that absolute values cannot be reliably determined. We have therefore chosen to express the results for IgG subclass activities on a relative basis with reference to units of total IgG activity against the same antigen in each subject. This approach is practical and appears scientifically acceptable but limits the use of such determinations to comparisons between groups of subjects studied in the same laboratory.

Direct detection of influenza virus antigen in nasopharyngeal specimens by direct enzyme immunoassay in comparison with quantitating virus shedding

We developed a direct enzyme immunoassay [EIA; Enzygnost Influenza A(Ag) and Enzygnost Influenza B(Ag)] for the direct detection of influenza A and B virus antigens in nasopharyngeal secretion specimens (NPS). The test is performed without sonification of specimens, and results are obtained within 4 h. A direct comparison between direct EIA and quantitation of virus shedding for influenza A and B virus antigen detection was carried out. A total of 210 NPS and 98 nasopharyngeal wash specimens (NPW) were investigated. We isolated influenza A viruses from 79 (37.6%) of 210 NPS; of these 79 cell-culture-positive NPS, 70 (88.6%) were also positive by direct EIA. Of 29 (13.8%) NPS from which influenza B virus was isolated, 24 (82.8%) NPS were positive by direct EIA. Virus shedding was determined quantitatively in 48 NPS from patients with influenza A and in 24 NPS from patients with influenza B. Only a crude correlation between optical density values and virus concentrations was observed. Detection of influenza virus antigens in NPS by direct EIA showed sensitivities of 89.7% for influenza A virus and 87.9% for influenza B virus and specificities of 99.3% for influenza A virus and 100% for influenza B virus. With direct EIA, all NPW were negative for influenza A virus, although virus was isolated from 21 (21.4%) NPW. Of 15 NPW from which influenza B virus was isolated, 7 showed positive results in direct EIA. In addition, direct EIA is suitable for detecting influenza A and B viruses in cell cultures before the appearance of any cytopathic effects and can be used as a cell culture confirmation test.

Sensitive avidin-biotin amplified fluorogenic enzyme immunoassay using biotinylated monoclonal antibodies for the identification and quantitation of virus

A highly sensitive amplified fluorogenic enzyme-linked immunosorbent assay (FELISA), which utilizes the high affinity interaction of the vitamin biotin for the multiple binding sites on the glycoprotein avidin, was developed for the detection and identification of a model virus, Newcastle disease virus (NDV). Monoclonal antibodies (MCA) directed against the virus were purified and labelled with biotin. Biotinylated MCA was then used with avidin-labelled enzyme and a fluorogenic substrate to detect NDV adsorbed directly on nitrocellulose membranes. Reagents were standardized and, using purified virus, the theoretical lower limit of test sensitivity of the amplified FELISA was determined to be 1 fg/ml of test sample (50 ag/well). The specificity of the amplified FELISA was evaluated by challenging the assay system with homologous and heterologous strains of NDV, and with other serologically related and unrelated viruses. The test was simple to perform and multiple samples could be conveniently assayed with results obtainable in 3-4 h.

A comparison of direct immunofluorescence, shell vial culture, and conventional cell culture for the rapid detection of influenza A and B

Direct immunofluorescence (FA) and shell vial contrifugation cultures (SVCs) were compared with conventional tube cultures for the rapid detection of influenza A and B by using a commercial antibody. Of the 439 specimens tested, 82 were positive by conventional culture (CC). The direct smear prepared from pelleted cells or direct swab material exhibited positive fluorescence in only seven (8.5%) of these cases, whereas the SVC was positive in 30 (37%). The SVC method detected 12 additional positive isolates that were not recovered in CC. The mean time to isolation in CC was 3.6 days for influenza A and 4.3 days for influenza B. The use of SVC provided more rapid results (36-48 hr). The FA method, although more rapid, may be of limited sensitivity and difficult to interpret depending on the quality of the specimen. The results indicate that SVC complements conventional culture in the rapid detection of influenza and can detect infections that may be missed in conventional tubes, but should not be used to the exclusion of conventional culture.

Comparison of Directigen FLU-A with viral isolation and direct immunofluorescence for the rapid detection and identification of influenza A virus

Directigen FLU-A, an enzyme immunoassay membrane test, was compared prospectively to isolation in cell culture and direct immunofluorescence (IF) for the detection of influenza A virus. One hundred ninety specimens were evaluated by Directigen FLU-A and cell culture; 184 of these specimens were also tested by direct IF. The sensitivity of Directigen FLU-A compared to isolation in cell culture and direct IF was 100%. The specificities of Directigen FLU-A compared to isolation and direct IF were identical, 91.6%. Fourteen specimens that were positive by Directigen FLU-A did not yield virus in culture; two of the specimens, however, were positive by direct IF, and four other specimens were not specimens of choice for the test. A positive Directigen result had positive predictive values of 62.6 and 75.0% compared to isolation and direct IF, respectively; a positive Directigen result with an intensity reading of 2+ or greater, however, had positive predictive values of 85 and 100% compared to isolation and direct IF, respectively. In all comparisons, the negative predictive value was 100%. There was no evidence that cross-reactivity occurred with non-influenza A antigens. Directigen FLU-A should serve as a convenient screening test for influenza A and as a rapid test supported by isolation in cell culture during an influenza outbreak.

Comparison of enzyme-linked immunosorbent assay, indirect immunofluorescence assay, and virus isolation for detection of respiratory viruses in nasopharyngeal secretions

Nasopharyngeal secretions obtained from 94 children with acute respiratory illness were examined for the presence of respiratory syncytial virus (RSV), adenovirus, and influenza virus type A by virus culturing (virus isolation technique [VIT]), immunofluorescence assay (IFA), and enzyme-linked immunosorbent assay (ELISA). Similar results were obtained in at least two tests for RSV, influenza virus type A, and adenovirus in 92 (97.9%), 88 (93.6%), and 88 (93.6%) cases, respectively. Both rapid virus detection methods showed good specificity for the diagnosis of these virus infections (greater than or equal to 90.7%) and were more sensitive than was VIT for RSV detection. In a more accurate statistical analysis, the indexes of agreement between VIT and ELISA were substantial for RSV (kappa = 0.69; zeta = 5.5; P less than 0.0001), influenza virus type A (kappa = 0.67; zeta = 5.3; P less than 0.0001), and adenovirus (kappa = 0.71; zeta = 6.0; P less than 0.0001), while it was almost perfect for RSV when ELISA was compared with IFA (kappa = 0.88; zeta = 5.7; P less than 0.0001). Although the observed agreement was good in the comparison of these two tests for these three viruses (89%0, the indexes of agreement were moderate in the comparison of IFA and VIT for RSV (K = 0.55; Z = 2.0; P < 0.05), influenza virus type A (K = 0.42; Z = 9.7; P < 0.0001), and adenovirus (K = 0.41; Z = 6.5; P < 0.0001) and of ELISA and IFA for influenza virus type A (K = 0.55; Z = 7.0; P < 0.0001) and adenovirus (K = 0.59; Z = 6.8; P < 0.0001). All of the statistical evaluations demonstrated better agreement between ELISA and VIT for influenza virus type A and adenovirus.

Evaluation of combined commercial enzyme-linked immunosorbent assay for detection of rota and adenoviruses for automation

219 stools were examined by direct electron microscopy (EM), culture and 'combined' commercial enzyme-linked immunosorbent assay kits (CELISA). The specificity of the combined ELISA for rotavirus was 100% as compared with EM, and 100% for adenovirus when both culture in addition to EM were carried out. ELISA appeared to be more sensitive than EM for both viruses. There was no cross-reaction between the 2 'combined' antisera. This technique may be useful for automation of viral diagnosis with ELISA using a 'panel' of selected viruses for a variety of specimens.

Rapid detection of respiratory syncytial virus and influenza A virus in cell cultures by immunoperoxidase staining with monoclonal antibodies

Peroxidase-labeled monoclonal antibodies against respiratory syncytial virus (RSV) and influenza A virus were used for immunoperoxidase staining (IPS) of cell cultures inoculated with nasopharyngeal aspirates. Cells were grown in 24-well plates, and specimens were inoculated by low-speed centrifugation. Cultures were incubated for 2 days at 37 degrees C and then fixed, stained, and observed by light microscopy. IPS was compared with standard virus isolation by using cultures of human diploid fibroblasts and Vero, HEp-2, and HeLa cell lines for RSV and Madin-Darby canine kidney cells for influenza A virus; these cultures were inoculated with specimens that were previously stored at -70 degrees C. Of 40 known RSV-positive specimens, 30 were found to be positive on reinoculation by both methods, and an additional 5 specimens were found to be positive by IPS only. Of 190 specimens tested for influenza A virus, 14 were positive by IPS and in tubes, and a further 8 specimens were positive by IPS only. IPS was also compared with direct detection of viral antigens in nasopharyngeal aspirates by a time-resolved fluoroimmunoassay (TR-FIA). Fresh nasopharyngeal aspirates were inoculated into human diploid fibroblasts and Madin-Darby canine kidney cells and tested for RSV and influenza A virus, respectively, by IPS. Of 110 specimens tested for RSV, 37 were positive in total, 32 were positive by IPS, and 33 were positive by TR-FIA. Of 150 specimens tested for influenza A virus, 39 were positive in total, 35 were positive by IPS, and 34 were positive by TR-FIA. IPS of cultures inoculated by centrifugation and incubated for 2 days is a sensitive method for the diagnosis of respiratory virus infections, and 24-well plates allow for the easy processing of a large number of specimens.

Sensitive enzyme immunoassay for the rapid diagnosis of influenza A virus infections in clinical specimens

Samples of nasopharyngeal secretion (NPS) from 100 infants and small children admitted for acute respiratory disease during the period from January to March 1989 were examined for the presence of influenza A virus. All samples were tested by enzyme immunoassay (EIA), fluorescent antibody (FA) technique and by isolation in cell culture 3-6 h after they were obtained from the patients. Of 24 influenza strains found by isolation, 21 were detected by EIA and 19 were FA+. In comparison with virus isolation, EIA gave the following values: sensitivity 88%, specificity 100%, positive prognostic value (PPV) 100%, and negative prognostic value (NPV) 96%. A rabbit anti-influenza-A serum (A-13) was used as catching antibody and a monoclonal anti-influenza-A pool against NP protein was used as detector antibody in EIA. A-13 gave bands corresponding to influenza A core proteins (NP and M1) in Western blot (WB) studies when different H3N2 strains were employed as antigens. A-13 gave only a band corresponding to the NP protein when H1N1 strains were examined by WB. The detection level by EIA for both H3N2 and H1N1 strains precipitated by polyethylene glycol from tissue culture maintenance medium was 1-2 ng.

Detection of influenza virus by centrifugal inoculation of MDCK cells and staining with monoclonal antibodies

Two methods for detection of influenza virus in 451 clinical respiratory specimens were compared: (i) 24-well-plate centrifugation with Madin-Darby canine kidney (MDCK) cells and staining with monoclonal antibody pools to influenza viruses A and B (Centers for Disease Control, Atlanta, Ga.) in an indirect immunofluorescence assay after incubation for 40 h, and (ii) conventional tissue cell culture with primary monkey cells and hemadsorption. For 100 of these specimens, direct examination of smears by the direct fluorescence assay with monoclonal antibodies (Boots Cell Tech/API Analytab Products, Plainview, N.Y.) was also performed. Influenza A virus was recovered from 28 specimens by tissue cell culture after incubation for an average of 4.75 days (range, 2 to 14 days). Influenza B virus was recovered from 35 specimens by tissue culture after incubation for an average of 5.4 days (range, 3 to 14 days). By the centrifugation assay, 23 specimens were positive for influenza A virus and 30 were positive for influenza B virus. All specimens positive by the centrifugation assay were also positive by conventional tissue cell culture. The sensitivities of the centrifugation assay were 82% for detection of influenza A virus and 86% for influenza B virus (84% overall); the specificity of the assay was 100%. Of the 100 specimens studied by direct examination, 15 were positive for influenza virus by both conventional culture and centrifugation assay; however, the direct-smear results for these 15 specimens were negative in 13 cases and inconclusive in 2. The centrifugation assay is a rapid and specific method for detection of influenza A and B viruses in clinical specimens, and it can serve as a valuable and cost-efficient adjunct to conventional culture methods.

Rapid diagnosis of influenza infection of NP antigen using an immunocapture ELISA test

An immunocapture ELISA test for the diagnosis of human and animal influenza A and/or B is described. A monoclonal anti-nucleoprotein (NP) antibody was used to capture the NP antigen and the captured antigen was detected by an anti-NP polyclonal rabbit antiserum. Compared with the usual diagnostic method by cultivation in embryonated eggs, this test had a high specificity (97%) and sensitivity when used for diagnosis using clinical nasopharyngeal samples obtained from patients and animals. Immunocapture ELISA permitted an easier reading than the indirect immunofluorescence technique. It also permitted diagnosis in frozen samples (-20 degrees C) or in infected LLCMK2 cells mixed with uninfected nasopharyngeal cells and kept at 20 degrees C for one week. This test can be carried out in 3 h.

Comparison of three techniques for detection of respiratory viruses in nasopharyngeal aspirates from children with lower acute respiratory infections

A comparison of immunofluorescence (IF), enzyme-linked immunosorbent assay (ELISA), and isolation in tissue culture (TC) for detection of respiratory viruses was performed on 496 nasopharyngeal aspirates from children under 5 years of age with lower acute respiratory infections who were receiving attention at three hospitals in Buenos Aires, Argentina. All samples were tested by the three methods for respiratory syncytial virus (RSV), influenza A and B, adenovirus, and parainfluenza 1 and 3. Viral diagnosis was made in 167 samples (33.7%); of these, 124 (74.3%) were isolated in TC, whereas 120 (71.8%) were detected by ELISA and 127 (76%) by IF. RSV was detected in 121 samples, mainly by ELISA and IF. The sensitivity and specificity of each rapid technique as compared with isolation in TC were similar, reaching 98% and 92%, respectively. When ELISA was compared with IF, the sensitivity was 95%, and the specificity was 98%. Adenovirus was detected in 18 patients by TC. For this virus, rapid techniques sensitivity as compared with TC was low (almost 22%). Parainfluenza 3 was readily detected by IF and TC; influenza A, B and parainfluenza 1 were detected in few samples; and tissue culture proved more efficient than rapid techniques. The results indicate that both rapid techniques are good tools for the detection of most respiratory viruses except for adenovirus, for which TC cannot be omitted.

Detection of bluetongue virus antigens in Culicoides variipennis by enzyme immunoassay

A solid-phase enzyme immunoassay (EIA) was developed to detect bluetongue (BT) virus antigens in infected cell cultures and in suspensions of infected Culicoides variipennis midges. The technique was equally sensitive for detecting the five U.S. BT virus serotypes (2, 10, 11, 13, and 17) in cell cultures. EIA reliably detected about 3.8 log10 median tissue culture infective doses per ml of BT virus in infected cell culture lysates. The EIA readily detected virus antigens in pools of midges infected with BT serotypes 2, 10, 11, 13, and 17 and contained 2.3 to 4.8 log10 median tissue culture infective doses per ml of BT virus. The technique was sensitive enough to detect a single infected midge in a pool with 99 noninfected midges. The EIA may be a sensitive and rapid alternative to virus isolation for surveillance of BT viruses in vector populations.

Rapid 24-well plate centrifugation assay for detection of influenza A virus in clinical specimens

Two methods for detection of influenza virus in 234 clinical respiratory specimens were compared: (i) a 24-well plate-centrifugation assay using Madin Darby canine kidney (MDCK) cells and staining with monoclonal antibody pools to influenza A and B (Centers for Disease Control, Atlanta, GA) after incubation for 16 h and 40 h, and (ii) conventional tube cell culture using MDCK cells and primary rhesus monkey kidney cells. Influenza A was identified in 23 specimens (10%). No influenza B was recovered. The rapid centrifugation and tissue culture methods were positive for influenza A in 21 (91%) and 16 (70%) of the 23 specimens, respectively. Fourteen specimens were positive by both methods, 2 were positive by tissue culture alone, and 7 were positive by rapid centrifugation only. Of the 21 specimens positive by rapid centrifugation, 16 (76%) were detected after overnight incubation, and 5 (24%) were positive only after incubation for 40 h. Cytopathic effect was observed in 13 (81%) of the 16 isolates identified by tissue culture after an average of 6 days, and 3 (19%) were identified only by hemadsorption and staining with monoclonal antibodies at day 10. Compared with conventional tissue culture, the 24-well plate centrifugation assay is a more rapid and more sensitive method for detecting influenza virus in clinical specimens.

Rapid and accurate viral diagnosis

In recent years, there has been increased recognition of the importance of viral infections. In addition, new antiviral agents have become available. These factors have led to a marked increase in utilization of viral diagnostic services. In this review, both conventional and rapid methods for viral diagnosis are presented, with emphasis on recent advances. The antiviral agents currently available and the major drugs under investigation are also briefly discussed. It is hoped that this review will serve as a useful adjunct for the management of patients with virus infections.

Sensitive fluorogenic enzyme immunoassay on nitrocellulose membranes for quantitation of virus

A highly sensitive fluorogenic enzyme-linked immunosorbent assay (FELISA), which utilizes nitrocellulose membranes as solid phase support, has been developed for the detection and identification of virus in clinical samples. Reagents were standardized and, using purified Newcastle disease virus (NDV) as a model, the theoretical lower limits of test sensitivity of the FELISA were compared, in both "sandwich" and "indirect" formats, to those of a comparable chromogenic enzyme-linked immunosorbent assay (CELISA). Of the systems evaluated, the "sandwich" FELISA exhibited maximum sensitivity and detected 10 fg of purified virus protein per milliliter of test sample (500 ag per test volume). Specificity of the "sandwich" FELISA was evaluated by challenging the system with heterologous strains of NDV and with other serologically related and unrelated viruses. In a clinical trial in which fecal materials from chickens undergoing vaccination with NDV were assayed directly by FELISA, the virus was detected from the first to approximately the tenth day post-vaccination. The test is simple to perform and results can be obtained in approximately 4 h.

Enzyme-linked immunosorbent assay of core antigens for clinical diagnosis of influenza

A solid-phase enzyme-linked immunosorbent assay (ELISA) with monoclonal secondary antibodies was used to detect matrix protein and nucleoprotein of influenza A. The sensitivity of the ELISA for highly purified A/Brazil nucleoprotein and matrix protein was 0.05 and 1.0 ng, respectively. Nasal washes from 10 of 20 adult subjects with culture-proven, naturally acquired infection caused by A/Brazil/11/78-like influenza virus were positive in the test, and 2 of 13 subjects with rhinovirus infection were falsely positive. To determine if ELISA results could be improved, nasal washes were obtained from 21 adult volunteers who had been inoculated intranasally with wild-type A/Korea/1/82 (five subjects) or A/Korea recombinants with matrix protein or RNA-2 protein of A/Ann Arbor/6/60 (16 subjects), and the nasal washes were processed by a variety of methods. Prompt addition of sodium azide to the nasal washes to limit bacterial growth, avoidance of freezing, and the use of an antiproteolytic agent all failed to improve ELISA results noticeably. Under the best conditions, ELISA was positive in only 12 of the 21 experimentally infected subjects and in 1 of 15 uninfected controls. Positive ELISA results in experimentally infected subjects correlated significantly with the titer of live virus in the nasal washes (r = +0.506; P less than 0.001). Detection of gradient-purified whole influenza virus or isolated core antigen in ELISA was inhibited by prior incubation with nasal washes, and the inhibitory activity was only partly decreased by heat treatment of the secretions. At present, the use of ELISA for detection of influenza antigens in respiratory secretions is not sufficiently sensitive or specific for routine laboratory diagnosis of influenza.

Rapid diagnosis of influenza A and B by 24-h fluorescent focus assays

Murine monoclonal antibodies directed against type-specific antigens of influenza A and B viruses have been shown to be useful diagnostic reagents for the detection of influenza viruses by immunofluorescence testing of nasopharyngeal cells. We have developed fluorescent focus assays utilizing these antibodies in cell culture chamber slides and shell vials for the rapid diagnosis of influenza A and B. Chamber slide assays were compared with virus isolation in 160 specimens from 135 patients with symptoms of influenza. Virus isolation was compared with immunofluorescence testing in 38 of the 160 specimens. Compared with virus isolation, 24-h cell culture chamber slide assays had a sensitivity of 75% and a specificity of 96%. Immunofluorescence testing of nasopharyngeal cells was only 38% sensitive and 91% specific. Shell vial assays were compared with virus isolation for 89 specimens. At 16 to 18 h postinoculation, the shell vial assay was 84% sensitive and 100% specific. We conclude that both chamber slide and shell vial assays are rapid, sensitive, and specific techniques for the diagnosis of influenza.

Rapid etiological diagnosis of pneumonia in young men

The major findings and conclusions of the present study are: 1. Evidence of the etiology of the pneumonia was established in 86% of 106 young men with pneumonia. Pneumococcus was the most common etiologic agent; it was detected definitely in 30% of the pneumonia patients, and possibly in another 20%, by blood culture, sputum culture, antigen detection, and serological methods. 2. Pneumococcal antigen detection from purulent pretreatment sputum samples was the best rapid diagnostic method for pneumococcus; it was capable of identifying 90% of the pneumococcal pneumonias definite by our criteria, whereas sputum Gram stain was positive in 65% of these. 3. Detection of adenoviral antigens from nasopharyngeal specimens (NPS) by EIA or IF method or adenovirus DNA by HYB method showed good specificity but a somewhat lower sensitivity than did adenovirus isolation from NPS. 4. Adenovirus antigens and DNA can be demonstrated also from sputum specimens. 5. EIA is slightly superior to the CF method in detecting antibody responses to adenovirus, but the detection of different antibody classes offers no additional diagnostic possibilities. 6. Isolation of Mycoplasma pneumoniae from bronchoalveolar fluid in pneumonia patients is a specific and sensitive method in the diagnosis of mycoplasmal pneumonia. 7. It seems possible to differentiate by clinical signs and symptoms and by high CRP (over 85mg/1) and WBC (over 10 x 10(9)/1) values pneumococcal pneumonias from viral, mycoplasmal and mixed pneumonias and from upper respiratory infections. Moderately elevated CRP values were observed in adenoviral (Mean 50 mg/1) and in mycoplasma (mean 59 mg/l) pneumonias, as well as in MRI (mean 44 mg/l).

Time-resolved fluoroimmunoassay with monoclonal antibodies for rapid diagnosis of influenza infections

Monoclonal antibodies that are broadly reactive with either influenza A or influenza B viruses were used to develop a 2- to 3-h antigen capture time-resolved fluoroimmunoassay (TR FIA) for detecting influenza viral antigens in both original nasopharyngeal aspirate specimens and in tissue cultures inoculated with nose or throat swab specimens. The lower limit of sensitivity of the assay was about 10 pg of protein as determined with purified influenza A nucleoprotein expressed by recombinant DNA. When the TR FIA was performed with 96 nasopharyngeal aspirate specimens collected during outbreaks of influenza A (H3N2) virus and the results were compared with serodiagnosis results with paired sera, the specificity and sensitivity of TR FIA for the demonstration of influenza A infections were 95 and 85%, respectively. In culture confirmation assays, more than 80% of the swab specimens that grew influenza A or B virus within 7 days could be identified by the TR FIA within 48 h of the inoculation of cells. The results are consistent with those previously reported for respiratory syncytial virus and extend the applicability of monoclonal antibody-based TR FIA for the rapid diagnosis of acute respiratory viral infections.

Rapid diagnosis of respiratory adenovirus infections in young adult men

Rapid viral diagnosis was attempted in 106 military conscripts with pneumonia and in 101 military conscripts with other types of respiratory infections. Nasopharyngeal suction specimens (NPS) were assayed for viral antigens by immunofluorescence and enzyme immunoassay (EIA). Sputum specimens from 97 pneumonia patients were assayed for viral antigens by EIA. Also, 71 NPS and 13 sputum specimens were examined for the presence of adenovirus DNA by a sandwich hybridization (HYB) method. The reference test was adenovirus isolation in cell culture from the NPS. Adenoviruses were isolated from 6 pneumonia patients and from 20 patients with other respiratory infections. Of these 26 NPS, rapid diagnosis was successful in 13, 16, and 14 cases by EIA, immunofluorescence, and HYB, respectively. Four antigen-positive specimens were found among the 181 specimens which were negative by virus isolation. Sputum was found to contain adenovirus antigen by EIA in 5 of 97 tested specimens. Of these 97 specimens, 13 were selectively tested in HYB, and a positive signal was observed in 4 cases. Serological testing of paired sera revealed 23 adenovirus infections in the pneumonia group and 42 in the group with other respiratory infections. Other viral infections were found only sporadically. All rapid virus detection methods showed excellent specificity but had a lower sensitivity (60%) than virus isolation. Our results show that rapid methods for diagnosing respiratory adenovirus infections can be successfully used in selected groups of adults.

Detection of respiratory syncytial virus in nasopharyngeal secretions by enzyme-linked immunosorbent assay, indirect immunofluorescence, and virus isolation: a comparative study

An enzyme-linked immunosorbent assay (ELISA) was developed for the detection of respiratory syncytial virus (RSV) antigens in nasopharyngeal secretions (NPS) from children with acute respiratory disease. Antisera against RSV nucleocapsids were used as immunoreagents for this test system. The results obtained by RSV antigen ELISA were compared to those of indirect immunofluorescence (IF) and tissue culture virus isolation (TC). Of the 404 NPS obtained, 278 were tested in parallel by ELISA and IF and 205 by ELISA and TC, and 89 were screened in parallel by all three methods. The sensitivity of ELISA in relation to IF was 86.7%, the specificity 95.7%. Sensitivity and specificity obtained by ELISA were 89.9% and 94.4%, respectively, compared to TC. False-negative results were obtained with all three test systems used.

Laboratory procedures in adenoviruses. XII. Comparison of five ELISA methods for demonstration of hexon antigen

To demonstrate adenovirus hexon, four different arrangements of a four-layer ELISA, to be performed with commercially available reagents, were compared with a three-layer ELISA. After evaluation of specific and control reagents and their dilutions, the guinea pig/rabbit or the rabbit/chicken method were equally practicable and sensitive as the three-layer method with rabbit serum and superior to two other methods. By testing about 100 stool samples and 74 throat swabs containing adenoviruses, it turned out that the sensitivity (1 ng/ml hexon) appears satisfactory for stool specimens in adenovirus enteritis of infants, but is much less sensitive than isolation in cell culture for adenoviruses in throat swabs. As confirmatory test, specimen were incubated with an adenovirus rabbit antiserum or normal serum and then tested.

Immunoenzymatic staining of viral and chlamydial antigens in cell culture

Methods are described for the conjugation of antibodies with biotin and for the use of these reagents in an immunoperoxidase staining procedure for infected cell cultures. This technique provides a simple, rapid, and specific approach to the identification and characterization of a number of viral and chlamydial isolates in the diagnostic laboratory.

Placental alkaline phosphatase in benign and malignant endometrium

The presence of placental alkaline phosphatase has been demonstrated immunohistochemically using a monoclonal antibody, in frozen sections of human endometrium. The enzyme is present in glandular epithelium, but is found most commonly in the surface epithelial layer throughout the menstrual cycle. It has also been demonstrated in malignant endometrial epithelium in eight out of twelve patients.

Detection of respiratory virus antigens in nasopharyngeal secretions from patients with acute respiratory disease by radio-immunoassay and tissue culture isolation

An investigation was made of the sensitivity and specificity of four-layer radio-immunoassays (RIA) in the detection of adenovirus, respiratory syncytial virus, influenza virus types A and B, as well as para-influenza virus types 1, 2 and 3 from nasopharyngeal aspirates of 146 patients with acute respiratory disease. The sensitivity of RIA was comparable with that of tissue culture isolation if the total number of positives is considered. The difference may have been caused both by a higher efficiency of the RIA for detection of inactivated or non-cultivable agents and by a higher efficiency of tissue culture methods if the samples contained only small amounts of antigen. Differences between the two antigen detection systems were found in particular with respiratory syncytial virus and influenza B virus. At present, the use of tissue culture isolation together with RIA is the optimal routine laboratory procedure for the diagnosis of respiratory infections.

Etiological diagnosis of influenza A virus by enzymatic radioimmunoassay

An enzymatic radioimmunoassay for influenza A virus was developed by using polystyrene beads coated with rabbit immunoglobulin G to capture viral hemagglutinins (H1 and H3). Captured hemagglutinin was detected with goat immunoglobulin G followed by affinity-purified rabbit anti-goat immunoglobulin G labeled with alkaline phosphatase. [3H]AMP was added to quantify alkaline phosphatase activity, and free [3H]adenosine was measured with a scintillation counter. The assay detected as little as 0.1 ng of purified hemagglutinin. It was specific for hemagglutinin subtype and, depending on the source of the goat immunoglobulin G used, detected either H1 or H3. There was no reaction with neuraminidase or core antigens of influenza strain WSN-33. The clinical efficacy of the assay was evaluated with sequential nasal washes from 33 patients with naturally acquired H1N1 influenza. In the first 3 days of infection, the assay was consistently less sensitive than the viral culture, although detectable antigen persisted in secretions longer than did the infectious virus. Testing of multiple samples greatly increased the number of individuals in whom an etiological diagnosis could be made by immunoassay (81% of patients were positive for viral antigens at some point in their illness), and such testing was necessary to achieve the sensitivity of a single culture. Mean antigen levels were highest in nasal washes with the highest titers of infectious virus.

Nitrocellulose-enzyme-linked immunosorbent assay (NC-ELISA) - a sensitive technique for the rapid visual detection of both viral antigens and antibodies

A modification of the enzyme-linked immunosorbent assay (ELISA) is described for sensitive and rapid direct visual detection of antigens of four adenoviruses (Ad) and anti-Ad antibodies using nitrocellulose (NC) membrane discs as high-capacity solid phase. The NC-ELISA was performed in microtitre plates containing NC-discs. Small amounts of crude supernatants from Ad-infected cells as antigen were bound to the discs. Additional binding capacity was blocked with an excess of bovine serum albumin. The subsequent reaction of virus antigen with specific rabbit antibody was visualized using alkaline phosphatase-conjugated anti-rabbit IgG and histochemical substrates. The sensitivity of the NC-ELISA for the detection of Ad-antigens was found to be 8-10-fold higher than a conventional ELISA using polystyrene solid phase supports. The sensitivity levels were estimated to be similar comparing NC-ELISA and tissue culture assay results. The quantitative determination of anti-Ad antibodies by NC-ELISA showed 8-fold higher sensitivity compared to microneutralization test. The NC-ELISA could detect purified immunoglobulin at a level of 1 ng using a direct test procedure and 10 ng using the indirect method. The detection limits are good compared to other highly sensitive assays. The use of crude antigen combined with high sensitivity and easy technical performance makes the NC-ELISA useful as a tool for rapid viral diagnosis.

Rapid viral diagnosis

There has been much interest and activity in the development of techniques for rapid viral diagnosis which would allow successful intervention in the treatment of patients or their contacts or in the control of viral diseases in the community. The greatest emphasis has been on techniques that permit viral detection directly in the clinical specimen, since these avoid the need to cultivate the agent, are feasible for detection of viruses that cannot be cultivated, and can detect virus in specimens in which the agent is no longer infectious. Direct methods used for viral detection include electron microscopy and various immunoassays which are based on demonstrating reactivity of viral antigen in the specimen with known viral antisera. The use of immunoassays for more rapid identification of viruses isolated in laboratory host systems and for selective detection of viral antigen in inoculated cell cultures even before the agents produce an observable effect has been an important advance in viral diagnosis by the approach of isolation and identification. The reliability of all specific viral identification procedures depends on the use of high quality viral antisera. Some of the problems previously encountered in preparing satisfactory viral immune reagents are being overcome through the availability of highly specific monoclonal antibodies produced by cell hybridization techniques. Virus-specific IgM antibody assays for rapid diagnosis have been improved greatly through the use of a "capture" technique in which antibody to the human mu chain is used in the solid phase to separate IgM from other serum components which might compete with IgM antibody or give nonspecific reactivity, and also through the availability of highly specific monoclonal antibodies to the human mu chain. A variety of simple assays for determination of viral antibody status have been developed, and many are commercially available. The reliability of some of these antibody assays has been improved through the incorporation of more suitable controls and through better definition of interpretations which should be made from test results.

Comparison of a monoclonal antibody with a polyclonal serum in an enzyme-linked immunosorbent assay for detecting adenovirus

To develop and evaluate an enzyme-linked immunosorbent assay (ELISA) for detecting adenovirus antigens in which a group-specific monoclonal antibody to the adenovirus hexon is used, we studied two different ELISA test systems. The test system which was the most sensitive and specific was then compared in parallel tests with a similarly constructed ELISA in which a mouse polyclonal serum was used. Both the ELISA with the monoclonal antibody and that with the polyclonal serum detected purified hexon and 15 different adenovirus types with similar sensitivities. The two assays also showed no reaction with 23 heterologous viruses. Both tests detected adenovirus in stool and respiratory tract specimens tested for adenovirus by standard tissue culture techniques with similar sensitivities and specificities, but neither was sufficiently sensitive for routine testing of these types of clinical specimens. However, the ELISA with the monoclonal antibody proved to be a good test for the noncultivatable adenoviruses, detecting 12 of 12 stool samples that were positive by electron microscopy. The monoclonal antibody proved to be as sensitive and specific as the polyclonal serum and has the advantage that it can be produced in unlimited quantities and needs to be characterized only once.