A common, contagious respiratory infection caused by a virus. Incubation after exposure is 24 to 48 hours. Outbreaks of different forms occur almost every winter with varying degrees of severity.
Influenza affects both sexes and all ages.
Muscle aches, including backache. Cough, usually with little or no sputum. Recent illness that has lowered resistance. Chronic illness, especially lung or heart disease. People in semi-closed environments.