Illness occurs from 24 to 72 hours following exposure to the virus with abrupt onset of fever, chills, headache, muscle aches and pains, dry cough, sore throat and overwhelming weakness. Return to full health following three to five days of illness is usually drawn out and may take a week or more. Virus is shed in droplets produced by sneezing, coughing and ordinary conversation and may be present in respiratory secretions up to 24 hours before onset of illness. Persons may be infectious to others up to 5 days or more following onset of illness, although virus shedding usually decreases to low levels after three days. Virus shedding may extend to 10 days or longer in children and persons with immune deficiencies.
Hands often serve as a means of viral exchange.
Influenza virus may cause pneumonia or so weaken a person that other viruses or bacteria may cause pneumonia or other complications. Amantadine or rimantadine may be prescribed within 48 hours of onset of illness in order to lessen the severity of the illness and prevent complications. They also may be employed to prevent illness in persons to whom vaccine cannot be given. As a preventative they should be taken throughout the period of viral transmission. Persons 65 years of age and older are at increased risk of severe illness and complications often associated with death.