Mixed A and B epidemics also occur. In temperate zones, outbreaks tend to occur in winter. It can be confirmed by virus culture. In outbreak situations, special arrangements can be made with the WHO Collaborating Centre for Inuenza References and Research and the Commonwealth Serum Laboratories for the isolation of inuenza virus. It is predominately transmitted by airborne spread.
Transmission also occurs by direct contact through droplet spread.
Direct contact may be important as the virus will survive some hours in dried mucus. Incubation Period Usually one to five days. When a new subtype appears, all are susceptible except those who have lived through earlier epidemics caused by a related subtype. Infection produces immunity to the specific infecting virus, but the duration and breadth of immunity depends on the degree of antigenic drift and the number of previous infections. Control of Case Symptomatic treatment only.