[Clinical and virological surveillance of influenza in Israel--implementation during pandemic influenza].

Background: Pandemic influenza surveillance has a central role in providing an updated situation for the health care system.

Aim: To describe the Israel Center for Disease Control (ICDC) pandemic influenza surveillance system.

Methods: The ICDC conducts a seasonal influenza surveillance system based on patients' visits to community clinics (mainly Maccabi Healthcare Services) and emergency rooms for influenza-like illness (ILI) or pneumonia, and on laboratory confirmed nasopharyngeal swabs from ILI patients at designated sentinel clinics (tested at the Central Virology Laboratory). The laboratory based surveillance provides data on the active influenza strains, resistance to anti-viral drugs and match with the seasonal vaccine. The influenza surveillance network was strengthened since the level of the influenza pandemic alert was raised to phase 4 at the end of April 2009.

Results: The first A/H1N1 2009 cases were identified by the surveillance system in the last week of May 2009. Local transmission was recorded in the second half of June 2009. At this time there was an increase in the rates of patient visits to outpatient clinics for ILI, especially in the age group 0-18 years old and in residents of Tel Aviv, Central and Jerusalem districts. By the end of July 2009 there was an increase in pneumonia cases (mainly 2-18 years old) in community clinics.

Conclusions: Once the pandemic influenza began spreading, the ICDC surveillance system provided a valid picture which facilitated the decision to stop laboratory confirmation of each community case and rely on the ICDC surveillance system as the main source for information.