Influenza surveillance in the Islamic Republic of Iran from 1991 to 2001.

To better understand the annual distribution of influenza virus in our country, we isolated and typed 45 viruses from 1043 patients with acute respiratory illnesses in a 10-year study conducted by the National Influenza Centre of the Islamic Republic of Iran. The seasonal distribution of influenza typically ran from November to April. Type A influenza was most common during the winters of 1991-92, 1997-98 and 2000-01 and type B influenza was most common during 1992-5 and 1996-97. Both type A and type B viruses circulated in 1995-96 and 1998-2000. A serological survey based on haemagglutination inhibition test confirmed our findings. The annual pattern of strains isolated was similar to the worldwide pattern during the same interval.