The introduction of the SENTINEL influenza surveillance system in Poland--experiences and lessons learned from the first three epidemic seasons.

Influenza surveillance provides information on virus activity and is necessary for the selection of vaccine strains and early warning. To improve this surveillance in Poland, a sentinel surveillance system was introduced in 2004-5 influenza season (SENTINEL). This paper presents results from SENTINEL during three seasons of its existence. Voivodship Sanitary-Epidemiological Stations (VSESs), physicians and the National Influenza Center (NIC) participate in SENTINEL. Laboratory course was performed by the NIC for VSESs. Stations were provided with procedures, report forms, etc. Physicians register number of influenza-like illnesses (ILI) and collect swabs. VSESs perform diagnostic tests. On the basis of information from VSESs, the NIC prepares weekly reports for the entire country. In 2004-5 epidemiological reports were received from 50% of VSESs, while in 2005-6 and 2006-7 from all VSESs. Virological reports were obtained from 37.5% of VSESs (2004-5), 75% (2005-6) and 94% (2006-7). Weekly number of reporting physicians ranged in three consecutive seasons from 165 to 219, 98 to 949 and 696 to 1,054. A total of 399 specimens were tested during the 2004-5 winter; 63 (16%) were positive for influenza and 21 (5%) for other respiratory viruses. In 2005-6, 949 specimens were tested. Influenza infections were confirmed in 47 cases (5%) and infections with other respiratory viruses in 36 cases (4%). A total of 1,195 specimens were tested during the 2006-7 winter; 37 (3%) were positive for influenza and 26 (2%) for other respiratory viruses. SENTINEL provided improvement of influenza surveillance when compared with seasons before 2004. Nevertheless, due to decreasing rate of positive specimens, virological surveillance is the most important part to improve in the next years.