Surveillance of respiratory viruses. A 10-year laboratory-based study.

Respiratory virus isolates made at the National Institute for Virology from 1982 to 1991 were studied. An active virus surveillance programme, 'viral watch', which recruits throat swab specimens from a network of monitoring centres--mainly in the Witwatersrand and Vereeniging area with one centre in Middelburg--that represent a cross-section of the population, provided 68% of the specimens and 74% of the isolates, with an isolation rate of 25.5%. This was significantly higher than that of routine specimens (17.7%). Of the 966 isolates, influenza viruses accounted for 527 (54.7%), para-influenza for 122 (12.6%), respiratory syncytial virus for 34 (3.4%) and adenovirus for 106 (11.0%). Influenza viruses showed a definite seasonal peak between June and August whereas the other viruses, although they showed a winter predominance, were isolated throughout the year. An active virus surveillance programme is particularly valuable in monitoring respiratory virus epidemiology in the population.