Influenza surveillance in Siena (Italy): 1994-1997.

Background. An effective surveillance system is an essential component of a program for the control of influenza. Aims. The study intends to examine the surveillance of influenza-like activity in Siena during the period 1994-1997. Methods. To this purpose the following parameters have been adopted: school and industrial absenteeism, mortality data, isolation and identification of viral strains and a study of the immunity status of the population. Results. In Siena, influenza activity in 1994-95 and 1995-96 was moder-ate. In the 1996-97 season we describe a low influenza activity. Conclusions. Overall the influenza activity in 1994-95, 1995-96 and 1996-97 was described as moderate. During the first study year, a virus A was first isolated and was identified as type A(H3N2) strain; in 1995-96 virus A was first isolated and was identified as type A(H1N1) and in the last epidemic year virus A was first isolated and identified as type A(H3N2). Children and young adults were most affected by the type A(H1N1) strain, whereas adults and older subjects by the type A(H3N2) strain.