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

Application of subtype-specific monoclonal antibodies for rapid detection and identification of influenza A and B viruses

We established a rapid method for the identification of influenza A and B virus strains: the peroxidase-antiperoxidase (PAP) staining method with two subtype-specific murine monoclonal antibodies, C179 (H1 and H2 specific) and F49 (H3 specific), and an anti-influenza B virus rabbit polyclonal serum. The types and subtypes of 160 strains were examined, and 158 strains were identified to be the same by the hemagglutination-inhibition (HI) test and the PAP method. In contrast to the results by the HI test, two strains were revealed to be a mixture of two subtypes (H1 and H3) by the PAP method, which was confirmed by plaque cloning. We further analyzed clinical specimens by the PAP method by directly inoculating specimens into Madin-Darby canine kidney cells in microplates. After 40 h of incubation, the types and subtypes of viruses in 52 of 152 specimens were clearly identified. Since the reactivities of the two monoclonal antibodies are not influenced by the antigenic drift of influenza virus, the newly developed method should be applicable not only for rapid diagnosis but also for the epidemiological study of influenza.

Microwave-accelerated direct immunofluorescent staining for respiratory syncytial virus and influenza A virus

A microwave-accelerated direct immunofluorescence staining method which requires only 20 min from specimen receipt to interpretation is as effective as conventional methods for detecting respiratory syncytial virus and influenza A virus antigens in clinical specimens. The time required compares favorably with that for the less sensitive Abbott Test Pack RSV.

Evaluation of a direct immunofluorescence assay, dot-blot enzyme immunoassay, and shell vial culture in the diagnosis of lower respiratory tract infections caused by influenza A virus

We prospectively evaluated the efficacy of two commercial rapid methods for antigenic detection, a dot-blot enzyme immunoassay (EIA-DB) (Directigen FluA, Becton-Dickinson, USA) and a direct immunofluorescence assay (DIF) (Monofluokit Influenza A, Diagnostics Pasteur, France), compared with the shell-vial culture in the MDCK line, incubated 2 to 3 days and stained with the monoclonal antibody clone IA-52, the diagnosis of lower respiratory tract caused by Influenza A virus (IA). In the study period the presence of IA virus was detected in 59 of the 377 samples analyzed (15.7%). Only the SVC method detected all positive samples (100% sensitivity), being used as a reference method for comparison with the other techniques). The EIA-DB technique detected 50 cases (84.7%) and the DIF only 35 (59.3%). In nine (15.2%) cases the diagnosis was obtained only with the SVC method. The results of the comparison of the EIA-DB technique with SVC were: sensitivity 84.7%, specificity 100%, positive predictive value 100%, and negative predictive value 97.2%. The DIF technique gave values of 59.3%, 100%, 100%, and 92.9%, respectively. A statistically significant difference was observed between the sensitivity of the EIA-DB and the DIF method (p = 0.0001). In view of the results we recommended the use of the EIA-DB as a screening method when infection by the IA is suspected. But to obtain the maximum diagnostic yield all samples would be inoculated in a shell vial culture with the MDCK cell line.

Differential diagnoses of influenza A virus, influenza B virus, and respiratory syncytial virus infections by direct immunofluorescence using mixtures of monoclonal antibodies of different isotypes

Differences between isotypes of monoclonal antibodies were employed to detect influenza A and B viruses and respiratory syncytial virus by direct immunofluorescence using fluorescein isothiocyanate or Texas Red conjugates. Examination of 56 specimens for influenza A and B viruses and 112 specimens for influenza A virus and respiratory syncytial virus showed the mixed-isotype test to be comparable to the conventional procedure.

Comparison of rapid immunofluorescence procedure with TestPack RSV and Directigen FLU-A for diagnosis of respiratory syncytial virus and influenza A virus

A rapid immunofluorescence format requiring 20 min for completion was as effective as conventional indirect and direct immunofluorescence procedures for detecting respiratory syncytial virus and influenza A virus antigens in clinical specimens. Rapid immunofluorescence was more sensitive than TestPack RSV and comparable to Directigen FLU-A immunosorbent assays, which require 20 min for completion.

Typing and subtyping of influenza viruses in clinical samples by PCR

Type A and B influenza viruses can cause a wide spectrum of illness, and these viruses are responsible for considerable mortality and morbidity. Rapid typing of isolates is desirable when amantadine treatment or prophylaxis of contacts of type A influenza virus carriers is considered, but the available rapid techniques lack sensitivity and standard diagnostic methods require expansion of virus in tissue culture or embryonated hens' eggs. We developed a series of oligonucleotide primers able to detect, type, and subtype type A influenza viruses in a single reverse transcription-PCR. RNA was isolated from clinical specimens, and cDNA was generated with random primers. PCR was carried out with a mixture of primers specific for influenza viruses of types B, A/H1 and A/H3, and subtyping of the neuraminidase was carried out on the same cDNA template under identical conditions. Amplified products were detected by ethidium bromide staining of amplified products after agarose gel electrophoresis. When it was used to test 98 clinical specimens, this method was comparable to standard culture techniques in the detection, typing, and subtyping of influenza viruses.

Monoclonal antibodies for the direct detection of influenza-A virus by ELISA in clinical specimens from patients with respiratory infections

BACKGROUND

Monoclonal antibody technology provides antibody reagents of known specificity, high titres and unlimited availability, that form ideal reference antibodies for use in specific viral antigen-detection methods.

OBJECTIVES

To produce mouse monoclonal antibodies against antigenic sites of influenza-A virus, and evaluate their use as diagnostic reagents in a sandwich ELISA.

STUDY DESIGN

(1) Production and characterization of monoclonal antibodies against influenza-A virus; (2) application of these antibodies in an ELISA method for direct antigen detection; and (3) evaluation of the ELISA as routine procedure.

RESULTS

Four monoclonal antibodies (A1-A4) from mice immunized intranasally with influenza-A virus were selected according to their specific reactivity with either nucleoprotein or matrix protein antigens as demonstrated by Western blot analysis. These antibodies lacked haemagglutination inhibition and neutralization properties and recognized both H1N1 and H3N2 strains of influenza-A virus equally. A sandwich ELISA using unlabelled antibodies for antigen capture and biotin-labelled antibodies for antigen detection was used to analyse nasopharyngeal secretions or nasal swabs from culture-confirmed influenza-A-infected patients and comparable specimens from patients with other viral respiratory infections. Only influenza-A virus (strains H1N1 and H3N2) could be detected in samples from patients with known influenza-A and influenza-B infections, and also after re-isolation of such viruses in conventional cultures of MDCK cells or embryonated hens' eggs. The antigen-detection assay showed a diagnostic sensitivity of 100% and a specificity of 98.3% compared with conventional culture methods.

CONCLUSION

The reported ELISA appears to be a rapid and inexpensive method for diagnosis and epidemiological studies of influenza-A infections.

Evaluation of Directigen Flu A assay for detection of influenza antigen in nasal secretions of horses

The Directigen Flu A assay (Becton Dickinson, Microbiology Systems, Mississauga, Ontario, Canada) is a commercially available immunoassay designed for rapid in vitro recognition of influenza A nucleoprotein. The purpose of this study was to evaluate this assay for detection of influenza virus in nasal secretions of naturally infected horses. The assay was shown to react with representative strains of influenza virus which cause disease in horses and did not react with nasal secretions from uninfected horses kept in isolation. Between 33% and 45% of nasal secretions specimens obtained from clinically diseased horses during influenza epidemics reacted positively in the assay and 95% to 98% of horses not showing signs of disease during influenza epidemics tested negative. In contrast, influenza virus was isolated from only 7% of diseased horses using conventional techniques. Diseased horses which were positive in the Directigen assay had lower pre-exposure influenza antibody concentrations and showed more clinical signs than diseased Directigen-negative horses. This evaluation demonstrates that the Directigen Flu A assay detects influenza virus in nasal secretions of infected horses and is more sensitive than virus isolation.

Routine diagnosis of seven respiratory viruses and Mycoplasma pneumoniae by enzyme immunoassay

A composite EIA, using 8-well microstrips, was used for the rapid detection of seven respiratory viruses and M. pneumoniae. The viruses included influenza A and B, parainfluenza 1, 2 and 3, adenovirus and respiratory syncytial virus. During the 61 month period--June 1988 to June 1993--17326 respiratory specimens, submitted from three states, were tested by this EIA. The specimens were mainly from a paediatric population (hospitals and private physicians). RSV was the predominant virus detected, followed by adenovirus, parainfluenza 3, M. pneumoniae, influenza A, parainfluenza 2, influenza B and parainfluenza 1. The use of blocking antibodies confirmed the identification of the agents, in particular with samples showing absorbance values greater than the cutoff with more than one infectious agent. Different methods for processing specimens in order to obtain a uniform suspension, and interpretation of non-specific reactions, are discussed. The assays showed an average sensitivity of 85% and specificity of 99%, compared to virus culture. This EIA system provided an efficient method for the rapid diagnosis of viral and mycoplasmal infections in a busy diagnostic laboratory.

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.

Comparison of rapid detection methods for influenza A virus and their value in health-care management of institutionalized geriatric patients

Respiratory specimens from 160 geriatric patients with suspected influenza illness were used to evaluate the abilities of two enzyme immunoassays (EIAs; Directigen FLU-A [Becton Dickinson Microbiology Systems, Cockeysville, Md.] and Prima EIA [Baxter/Bartels Diagnostics, Inc., Issaquah, Wash.]) and direct immunofluorescence testing (immunofluorescence assay [IFA]) to identify influenza A virus. In comparison with culture isolation, the sensitivities and specificities of the IFA, Directigen FLU-A, and Prima EIA were 92.5 and 97.2%, 86.8 and 99.1%, and 92.5 and 98.1%, respectively. In contrast to EIA, IFA was labor intensive and required a high degree of technical expertise, and the results of IFA were difficult to interpret. These factors may preclude the use of IFA for testing large numbers of specimens. A retrospective epidemiologic survey of influenza infection was done in six geriatric institutions which had used either rapid and culture testing or culture alone. Preventable cases of influenza A virus infection ranged from 9 to 38% of all cases in facilities which used culture testing only and which had not instituted amantadine prophylaxis. The use of direct specimen testing is recommended as an adjunct to culture isolation for the identification of influenza A virus. Use of a combination of these methods permits the timely administration of appropriate antiviral therapy and infection control measures, while it also permits the antigenic surveillance of circulating influenza strains, which is necessary for present vaccine efficacy evaluations and the creation of future effective vaccine formulations.

Comparison of rapid diagnostic techniques for respiratory syncytial and influenza A virus respiratory infections in young children

We performed virus isolation tests for respiratory viruses on combined nasal wash-throat swab specimens collected from infants and children with acute respiratory illnesses presenting to a hospital clinic during a 3-month period of concurrent epidemics of respiratory syncytial virus (RSV) and influenza A virus (Flu A) infections. Virus isolation results were used to assess the utility of commercially available rapid diagnostic kits for these two viruses. The kits employed direct immunofluorescence (IF) of cells (Imagen for RSV and Flu A), indirect IF of cells (Baxter Bartels Microscan), and enzyme immunoassay (EIA) (Becton Dickinson Directigen for RSV and Flu A and Abbott TestPack for RSV). All testing was completed on 81 specimens from 80 subjects. Of the 81 specimens, 53 (65%) yielded a virus: RSV, 28%; Flu A, 25%; rhinovirus, 6%; and enterovirus, cytomegalovirus, herpes simplex virus, and adenovirus, 2 to 4% each. Among the tests, Bartels Microscan and Directigen Flu-A exhibited the highest sensitivities (87 and 75%) and efficiencies (94 and 94%) for RSV and Flu A, respectively. All the tests exhibited high specificity. Thus, optimal detection of RSV and Flu A among infants and children who presented to a hospital clinic required two different detection methods (IF and enzyme immunoassay) and kits from two different companies (Baxter [Bartels Microscan] and Becton Dickinson [Directigen]).

Prospective application of reverse transcriptase polymerase chain reaction for diagnosing influenza infections in respiratory samples from a children's hospital

A prospective clinical evaluation of the reverse transcriptase polymerase chain reaction (RNA PCR) for detection of influenza viruses was carried out with specimens from 342 patients of a children's hospital in The Netherlands. The RNA PCR, carried out directly on the specimens without an organic extraction, showed a sensitivity and specificity which are superior to those of direct immunofluorescence and comparable to those of cell culture combined with immunofluorescence (culture/IF). Negative results can be obtained within 2 days by the RNA PCR but may take up to 14 days by culture/IF. Because culturing is the standard technique for the detection of respiratory viruses, at this moment there are no strong arguments to replace culture/IF with RNA PCR for the detection of influenza A virus.

Viral pneumonias. The increasing importance of a high index of suspicion

Viral pneumonias account for at least 17% of cases of community-acquired pneumonia in children and in adults. Although patients with viral pneumonia appear less ill clinically than those with bacterial pneumonia, viral pneumonias can be fatal. Antiviral therapy is available for pneumonias caused by respiratory syncytial virus, influenza A virus, and cytomegalovirus. Several vaccines are important tools for the prevention of influenza A and B pneumonia.

Isolation of seven respiratory viruses in shell vials: a practical and highly sensitive method

The isolation of respiratory viruses in shell vials was compared with isolation in tube cultures in order to determine the sensitivity of the former, rapid method. Twenty of 21 influenza virus and 15 of 15 parainfluenza virus isolates were recovered in shell vials. One hundred twenty-seven of 138 respiratory syncytial virus isolates were detected in shell vials, but only 10 of 21 adenovirus isolates were positive by the rapid method. Shell vials are very effective for the diagnosis of respiratory viral infections, except for those caused by adenovirus.

Evaluation of a rapid enzyme immunoassay for detection of influenza A virus

The Directigen FLU-A enzyme immunoassay for the detection of influenza A virus was compared with direct smear and culture in 211 clinical specimens. The FLU-A enzyme immunoassay proved to be a reliable, rapid screen for influenza A from symptomatic patients and was less dependent on technical expertise for interpretation than were direct smears.

Rapid detection of respiratory viruses using mixtures of monoclonal antibodies on shell vial cultures

Eleven hundred and thirty-three clinical specimens submitted to the laboratory for diagnosis of respiratory virus infections were tested by direct immunofluorescence (DIF) for respiratory syncytial virus (RSV), by shell vial culture, and by conventional cell culture. The shell vial cultures were stained with 8 different monoclonal antibodies both 1 day and 3-7 days after inoculation. In order to limit the cost and the workload, mixtures of monoclonal antibodies were used. Coverslips with HEp-2 cells were incubated with a mixture of FITC-labeled monoclonal antibody to RSV and nonlabeled monoclonal antibody to adenovirus. When no RSV positive IF staining was observed after the first incubation step, the same coverslip was incubated once more with FITC-labeled anti-mouse antibody. A positive reaction at this stage indicated the presence of adenovirus. Similarly, cultures of tertiary monkey kidney cells were investigated with a mixture of two FITC-labeled monoclonals to the influenza viruses A and B and three nonlabeled monoclonals to the parainfluenza viruses 1, 2 and 3. If influenza virus or parainfluenza virus was detected, the exact type was determined by staining different parts of a duplicate coverslip. Shell vial cultures for cytomegalovirus (CMV) were always performed separately on human embryonic lung fibroblasts. Using this approach, we detected RSV (n = 248), CMV (n = 42), parainfluenza virus (n = 31), influenza virus (n = 28), and adenovirus (n = 6), in most cases after only one day of culture. For RSV, the sensitivity of the shell vial method was too low (74%) to allow omission of DIF (sensitivity 95%).(ABSTRACT TRUNCATED AT 250 WORDS)

A nylon membrane enzyme immunoassay for rapid diagnosis of influenza A infection

A new membrane-enzyme immunofiltration assay (MIFA) was developed for rapid diagnosis of influenza A infection. The pretreated specimens were dispensed into a 1.2 micron Biodyne B nylon membrane-bottomed microplate and vacuum filtration was applied. Blocking solution, peroxidase-conjugated anti-influenza A nucleoprotein monoclonal antibody, washing buffer and substrate were added in that order. The assay was completed within 30 min. Out of 103 nasopharyngeal swabs collected in transport medium, 31 isolates of influenza A virus were obtained and 22 specimens were detected directly by the MIFA technique. The 9 isolation-positive MIFA-negative specimens required 6 days or more for viral detection in cell culture, and probably contained a very low quantity of virus. The 72 cell culture negative specimens were also negative by MIFA. Comparison with a classical immunocapture assay (ICA) gave a better sensitivity for MIFA, as only 15/103 specimens were positive by ICA. MIFA is a rapid test with 71% sensitivity and 100% specificity. It was also very useful to test the cell culture supernatants, as a sensitivity of 100% was obtained with MIFA when the immunofluorescence technique was positive. The same technique could be readily carried out on the same plate for other respiratory viruses since capture antibody is not used.

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.

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.

New aspects of influenza viruses

Influenza virus infections continue to cause substantial morbidity and mortality with a worldwide social and economic impact. The past five years have seen dramatic advances in our understanding of viral replication, evolution, and antigenic variation. Genetic analyses have clarified relationships between human and animal influenza virus strains, demonstrating the potential for the appearance of new pandemic reassortants as hemagglutinin and neuraminidase genes are exchanged in an intermediate host. Clinical trials of candidate live attenuated influenza virus vaccines have shown the cold-adapted reassortants to be a promising alternative to the currently available inactivated virus preparations. Modern molecular techniques have allowed serious consideration of new approaches to the development of antiviral agents and vaccines as the functions of the viral genes and proteins are further elucidated. The development of techniques whereby the genes of influenza viruses can be specifically altered to investigate those functions will undoubtedly accelerate the pace at which our knowledge expands.

Diagnostic virology--then and now

In the past five years, technologic advances in the shell vial assay and expanding availability of rapid membrane EIA tests have allowed over 90% of the viruses detected in our laboratory to be reported within 24 h postinoculation. PCR technology promises to add a new practical dimension to diagnostic virology especially for the detection of viruses in CSF, tissues, and blood. Extension of these diagnostic capabilities from investigative protocols to general laboratories for routine use will be our biggest challenge and be based on considerations of cost, licensing, and availability of this technology in "kit" formats.