Persons most commonly affected: All age groups and both sexes.

Organ or part of body involved: Respiratory tract.

Symptoms and indications: Symptoms usually develop one to three days after exposure to the virus. High fever, chills, headache, muscle ache, stiffness and total exhaustion can occur suddenly. A sore throat, cough and runny nose may follow.

Causes and risk factors: The cause of the infection is usually one of three main strains of flu virus, designated A, B and C, which are each sometimes responsible for epidemics of the disease occurring in cycles. Characteristically, infection with one strain does not confer immunity against another. Also, the virus quickly produces new variants or characteristics so that an attack of one is unlikely to provide protection against a later bout of the disease. Sometimes, complications can arise as a result of flu in the form of secondary lung infections. These can be dangerous in elderly people.

Prevention: Stay home and in bed to allow your body to recover and to prevent spreading your flu germs to other people. Get lots of sleep. Drink plenty of water. Wash your hands properly before you eat or prepare food, after you use the bathroom or change diapers, after you blow you nose, sneeze or cough into your sleeve, and before and after taking care of someone who is sick. Eat lightly to allow your body to focus on healing, rather than on digestion. Eat citrus fruits that are rich in vitamin C. Eliminate diary abd refined sugar products from your diet. Also avoid coffee, black teas, and chocolates until the flu passes.