Monitoring of influenza in Israel 1976/77.

The main objectives of the monitoring were: (1) to define the prevalent virus involved in influenza activity: (2) to determine the time of its occurrence; and (3) to evaluate its extent and impact. A sudden rise in the frequency of visits associated with acute respiratory conditions in the age group 0-14 to the emergency rooms of 14 hospitals throughout the country, correlated well with the start of influenza B/Hong Kong activity; this was simultaneously attested by two different laboratories. The later and sporadic occurrence of influenza A/Victoria activity did not affect the usual trend observed in the frequency of visits to emergency rooms. An age group stratified serologic follow-up pointed to a progressively increasing rate of influenza B infection up to the age group 15-24. A crude morbidity rate of 13-18% was recorded during influenza B outbreaks in several agricultural settlements. The percentage distribution of cases was about 15,21, 26 and 37 in the age groups 0-4, 5-9, 10-14 and 15+, respectively. The mortality associated with influenza B and influenza A activity did not exceed the expected rate.