Comparison of direct immunofluorescence of exfoliated cells (DIF), tissue culture immunofluorescence (TCIF) and conventional virus isolation (CVI) for the diagnosis of respiratory virus infections

Rapid direct diagnosis of mumps meningitis by ELISA capture technique

ELISA capture technique (ELISAc) was carried out using a rabbit hyperimmune serum attached to a solid phase for capturing mumps antigens in cerebrospinal fluid (CSF) in patients with meningitis and/or in supernatants of infected Vero cells. A biotin-labelled rabbit serum prepared from the previous serum was added and the reaction was read by an enzymatic (avidine-peroxidase) reaction by automated reading. The cut-off was calculated in 100 CSFs negative for viruses by conventional diagnosis. The specificity was evaluated in Vero cells infected with 22 CSFs collected from vaccinated children (URABE AM9 attenuated vaccine) who developed meningitis. A guinea pig hyperimmune serum confirmed the specificity. Results in culture correlated with the ELISA capture technique (ELISAc). No cross-reactivity was observed with parainfluenza 1, 2, 3 human reference strains. At least 2.5 ngs of purified mumps proteins were detected corresponding to 10(1.5) infectious particles per ml. ELISAc applied directly to 14 CSFs collected from unvaccinated children with meningitis diagnosed five positive cases, whereas in four cases conventional diagnosis had to be undertaken twice. ELISAc permitted the diagnosis of one additional patient. The test can be carried out in 3 h.

Rapid detection and typing of circulating mumps virus by reverse transcription/polymerase chain reaction

The reverse transcription/polymerase chain reaction (RT-PCR) was used to amplify a 129-bp fragment of the mumps virus F gene from strains circulating in the Siena area from 1993-1995. The nucleic acid was amplified directly from the samples; no growth in cell culture was required. Nucleotide sequence analysis and the comparison with other virus strains enabled the typing of the detected viruses. There appears to be more than one lineage of mumps virus circulating at any given time in the same location. A PCR assay coupled with the sequencing of the 5' end of the F gene seems to be a convenient method for characterizing mumps virus strains. This method, useful in diagnosis, also appears to be suitable for epidemiological studies.

Detection of respiratory syncytial virus infection in nasal aspirate samples by flow cytometry

Hypotheses: (i) Flow cytometry has the potential for rapid detection of respiratory viral antigens. (ii) This technique can be applied to viral diagnosis in clinical samples.

Objectives and study design: (i) To study the identification of six common respiratory viral pathogens by flow cytometry, in virus infected and uninfected cultured cells, as models of positive and negative clinical samples. (ii) To compare flow cytometry with the established techniques of viral isolation and immunofluorescent microscopy in the diagnosis of respiratory syncytial virus infection in 68 naso-pharyngeal aspirates taken from children and sent to the virology laboratory for routine virological diagnosis.

Results: (i) For each virus analysed, populations of infected and non-infected cells were clearly discernable, confirming potential for this method in rapid viral diagnosis in clinical samples. (ii) Two definitions were employed for a sample to be positive by flow cytometry, these were compared with the combined established techniques. The sensitivity, specificity, positive and negative predictive values of flow cytometry were 41%, 98%, 92% and 71% for the first definition and 74%, 88%, 80% and 84% for the second definition respectively.

Conclusions: As tested in this study, flow cytometry is less sensitive than established techniques as well as recently developed rapid diagnostic techniques for the diagnosis of respiratory syncytial virus infection. Further evaluation of the potential of flow cytometry in rapid viral diagnosis is warranted.

Rapid detection of mumps virus by the polymerase chain reaction

A procedure for detecting mumps virus in under 48 h was developed using the PCR. The sensitivity of the PCR amplification reaction and of the detection of the PCR product was significantly improved by: (i) enriching for viral template RNAs by overnight culture of the virus in Vero cells and (ii) substitution of polyacrylamide gel analysis for agarose gel electrophoresis. The technique was capable of detecting 1-20 infectious units of virus or an equivalent of 1-10 pg of mumps virus-specific plasmid DNA.

Evaluation of three rapid enzyme immunoassays and cell culture for detection of respiratory syncytial virus

Three rapid enzyme immunoassay techniques for the detection of respiratory syncytial virus antigen (Becton Dickinson Directigen RSV, Abbott RSV Testpack and Abbott RSV EIA) and cell culture were evaluated in a total of 250 nasal washings. The sensitivity and specificity were 62% and 76% respectively for Directigen, 64% and 86% for RSV Testpack, and 76% and 81% for RSV EIA, taking cell culture as the reference method. Agreement between cell culture and EIA techniques was 79% (70 positive and 128 negative results). All three EIA techniques gave positive results in 69 samples (52 positive and 17 negative in the cell culture). In 121 samples all three EIA techniques gave negative results (103 negative and 18 positive in the cell culture). Using the cell culture technique 46 strains other than respiratory syncytial virus were isolated.