by Harriet Squier

Created on: February 04, 2009

Influenza occurs mainly during the winter months in both the northern and southern hemispheres. Occasionally cases are reported during other times of year, presumably related to travel from other parts of the world. Influenza in tropical areas can occur at any time of year.

Outbreaks of Influenza A in a given area can begin quite suddenly and last for up to three months. Usually, children are the first to be affected, with fevers and cough. Adults come down with the infection next. Rates of infection can be suggested by absences from school or work. Typically, 10 to 20 percent of the population comes down with influenza, although severe occurrences, such as in pandemics, can affect half of the population. People who live in institutions are at increased risk of being infected.

Influenza B outbreaks are usually not as severe as Influenza A, and generally infect fewer people. Influenza B is most commonly found in schools and military bases and sometimes in nursing homes and cruise ships. It is usually not possible to tell the difference between Influenza A and Influenza B based on symptoms alone, as both illness start similarly.

Most people affected are maximally contagious the first day after exposure and continue to be contagious up to 10 days. The symptoms of influenza may not start for one to two days after a person has been exposed. The patient typically experiences sudden onset of cough and sore throat along with fever, muscle aches, headache, and weakness. However, there can be a wide variation in the symptoms of influenza in different people. In some, influenza looks like the common cold, with no other symptoms besides head congestion and cough. In others, the systemic symptoms, such as muscle aches, fever, and fatigue predominate, with few respiratory symptoms. These variations in presentation of influenza can make diagnosis challenging.

Controlling outbreaks of influenza can be challenging as well. Sick persons should be isolated from others if possible; children should be kept home from school and adults from work. Ill persons should wear masks if they cannot avoid contact with others. Frequent hand washing is essential as well. Prevention with influenza vaccines is the most successful means of minimizing influenza outbreaks. Vaccination is especially important for health care workers, children, the elderly, those with chronic diseases, and for residents of institutions and nursing homes. Occasionally, entire institutions, like colleges, may close down during severe outbreaks in order to halt further spread of infection.

Source: Up to Date

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