Influenza surveillance in N. Greece during 1983-1993.

Following the WHO programme to monitor influenza, the National Influenza Centre for N. Greece presents the results of a laboratory surveillance during 1983-93. Influenza viruses were isolated every year except for 1986-87 and 1987-88 seasons. Type A viruses predominated in 1983-84, 1985-86, 1988-89 and 1989-90. Type B viruses were prevalent in 1990-91 and 1992-93. Both types of A and B viruses circulated concurrently in the community during the winters of 1984-85 and 1991-92. Seroconversions (CF tests) occurred each year against A, B or both types of influenza viruses. In 1986-87 and 1987-88 when no viruses were recovered, there were seroconversions to B viruses, suggesting influenza B activity in the area. Serological surveys by haemagglutination inhibition (HI) tests were also conducted in 1986-87 and 1988-89. The patterns of the isolated strains were similar to those recorded worldwide at the same time. There have been however differences in the virulence of the viruses and the duration of influenza seasons in this part of the world during 1983-93.