Le diagnostic rapide des infections à virus respiratoire syncytial (RS) par le titrage des IgM sériques (immunofluorescence indirecte)

An epidemic of respiratory syncytial virus in elderly people: clinical and serological findings

In 1984-1985, an outbreak of respiratory syncytial virus (RSV) infection occurred in two geriatric wards. Among 68 patients (mean age +/- SD = 82.5 +/- 12.5 with respiratory signs, 52 had signs caused by RSV infection. Among all patients, the clinical and serological attack rates were 61.2% and 75.0%, respectively. The most frequent clinical presentation was intensive coughing (96.1%) and fever (96.1%) associated with expectorate (63.5%). The duration of the respiratory symptoms was 5 to 7 days. The disease gradually resolved, although in eight (15.4%) patients complications occurred. For periods of up to 1 year after infection, 172 sera were obtained and tested by complement fixation test (CFT), fluorescent assays for titrating specific IgG, IgA, and IgM, and Western blotting. Specific IgM appeared in six (11.5%) of the infected patients and peaked 2 to 6 months after infection, and there was no significant correlation with severity of clinical symptoms. However, higher peak G and A antibody responses were observed in persons with rales (CFT: P = 0.008; IgG: P = 0.042; IgA: P = 0.020), cough (IgG: P = 0.034), sputum (IgG: P = 0.030), dyspnea (CFT: P = 0.024), conjunctivitis (CFT: P = 0.025), and bronchitis (CFT: P = 0.018). The temporal patterns of IgA and CFT results were found to be similar, whereas IgG peaked later, i.e., between 2 and 6 months. The patients with the most severe symptoms had the highest antibody titers obtained by conventional tests and by Western blots. Thus, RSV can be an epidemic pathogen among elderly persons, although this illness is usually mild.

Rapid diagnosis of respiratory syncytial virus infection by antigen immunofluorescence detection with monoclonal antibodies and immunoglobulin M immunofluorescence test

During a respiratory syncytial virus (RSV) infection outbreak in a pediatric hospital, diagnosis was made by immunofluorescence on smears by using an anti-RSV monoclonal antibody (IFm). Immunoglobulins M and G were titrated by indirect immunofluorescence on HEp-2 cells infected with an RSV strain. The IFm was sensitive (89%) and specific (75%) when compared with the cell culture method. We showed that the specimens which were found positive by IFm and negative by cell culture were truly positive. Under these conditions, the IFm test appears more sensitive and more specific than cell culture, particularly when no care is taken to maintain the specimens in the cold during transport. In this study the immunoglobulin M immunofluorescence test had a low sensitivity (34%), especially on serum samples taken on days 0 to 4 after the onset of illness.