Influenza

A viral infection of the respiratory tract (air passages), typically causing fever, headache, muscle ache, and weakness. Popularly known as “flu”, it is spread by infected droplets from coughs or sneezes. Influenza usually occurs in small outbreaks or every few years in epidemics. There are 3 main types of influenza virus: A, B, and C. A person who has had an attack caused by the type C virus acquires antibodies that provide immunity against type C for life. Infection with a strain of type A or B virus produces immunity to that particular strain. However, type A and B viruses are capable of altering to produce new strains: type A has been the cause of pandemics in the last century. Types A and B produce classic flu symptoms; type C causes a mild illness that is indistinguishable from a common cold. The illness usually clears up completely within 7–10 days. Rarely, flu takes a severe form, causing acute pneumonia that may be fatal within a day or 2 even in healthy young adults. Type B infections in children sometimes mimic appendicitis, and they have been implicated in Reye’s syndrome. In the elderly and those with lung or heart disease, influenza may be followed by a bacterial infection such as bronchitis or pneumonia. Analgesic drugs (painkillers) help to relieve aches and pains and reduce fever. The antiviral drug amantadine may be given if the person is elderly or has another lung condition. Antibiotic drugs may be used to combat secondary bacterial infection. Flu vaccines, containing killed strains of the types A and B virus currently in circulation, are available, but have only a 60–70 per cent success rate. Immunity is short-lived, and vaccination (recommended for older people and anyone suffering from respiratory or circulatory disease) must be repeated annually.