Abstract

In the season 1992/93 the clinical influenza surveillance among general practioners participating in the NIVEL (Netherlands institute of primary health care) system was supplemented by RIVM with virological laboratory examinations. Respiratory samples were taken from 388 patients with respiratory symptoms suggestive of influenza. From 127 specimens (33%) a virus was isolated, which was influenza virus (mainly type B) in 87 cases. Compared with virological surveillance based on virus isolations from hospital admitted patients this new influenza surveillance system proved a better early warning system. The first influenza B virus strain of the season 1992/93 isolated in the Netherlands was isolated in this system about six weeks before the start of the epidemic. It was also more efficient: it yielded 43% of all influenza virus strains of the season 1992/93 isolated in the Netherlands. The period showing many clinical cases of influenza-like illness coincided with that in which many influenza viruses were isolated.