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Respiratory syncytial virus (RSV) is probably the single major cause of lower respiratory infection (LRI) among infants worldwide. Its relative importance may be underestimated, as the diagnosis is based on antigen detection and antigen may only be detectable in the early phase of infection. We have therefore assessed the duration of secretory IgM and IgA antibody responses and whether assays for these antibodies can be used to improve the diagnosing of RSV-associated infections. During two RSV epidemics in Guinea-Bissau, 32 RSV antigen-positive children with LRI were followed with sequential nasopharyngeal suction on days 7, 14, 30, 60 and 120 in the first epidemic and every fortnight for 6 mo after the second epidemic to measure the duration of secretory IgM and IgA responses. Nearly all of the children had an IgM response during the first month after infection. The response ratio was highest on days 7 and 14, being 84% and 71%, respectively. After 30 d the IgM response decreased rapidly. Among 27 age- and sex-matched controls, only 1 child was positive for IgM. During the second epidemic, when the children were followed more intensively, half of the children were IgM-positive after the acute phase of infection. A secondary response may be more likely in children with low IgM responses in the acute phase (RR = 2.08 (95% confidence interval (CI) 0.92-4.70)). The IgA response was highest on days 28 and 42 after antigen detection, 72% having a detectable IgA response within the first 1.5 mo. Among 27 controls, only 2 were IgA-positive (7%). In the second epidemic with more intensive follow-up, 62% (8/13) of the IgA-positive children had a response that lasted 10 wk. Of the children with no persistent IgA response, half (5/10) had a subsequent IgA-positive response after the first 42 d. All of these children had a simultaneous IgM-positive response. When 29 of the children were tested after an epidemic when they were 1-3-y-old, >80% again had high IgM (24/29, 82%) and IgA (28/29, 94%) levels. Among samples collected over a 1-y period from infants with LRI in a community morbidity surveillance conducted at the local health centre and via paediatric outpatient consultation, 17% (110/659) were antigen-positive, 26% (171/659) IgM-positive and 38% (248/659) either antigen- or IgM-positive. IgM responses are short-lived among infants and may therefore be used as an indication of recent RSV infection among children with LRI. Using both antigen and IgM detection may significantly improve our detection of RSV infections. [ABSTRACT FROM AUTHOR]

Objective: To compare detection of respiratory syncytial virus (RSV) for diagnostic purposes using nasopharyngeal aspirate (NPA) and nasal swabs (NS) in different clinical settings in a community study in Guinea-Bissau., Method: During 1996-98 paired specimens were obtained from 635 children under 5 years of age (median: 274 days; interquartile range: 144-453 days) with symptoms of lower respiratory infections (LRI). The specimens were analysed by an enzyme-linked immunosorbent assay for RSV antigen in Guinea-Bissau and re-analysed in Denmark using the same assay. The gold standard for RSV antigen detection was defined as any test being positive., Results: RSV antigen was detected in 84 (13%) children, the prevalence being 19% (41/219) among infants aged < 6 months, 12% (22/184) in infants aged 6-11 months, and 9% (21/230) in older children. Sensitivity of antigen detection was higher in NPA (92% in analyses in Guinea-Bissau and 98% in Denmark) than in NS (63% in analyses in Guinea-Bissau, 71% in Denmark). Specificity of RSV antigen detection was equally high in NPA and NS (99-100%). Time since onset of symptoms was significantly shorter in RSV antigen positive than negative samples. Sensitivity did not depend on clinical setting or age of the child., Conclusion: Using NS samples was associated with a 27-31% reduction in sensitivity compared with NPA specimens. As NPAs are costly and considered a nuisance by the population, it might be cost-effective in larger epidemiological studies to lose 25-30% in sensitivity but be able to collect samples from a much larger population.