Influenza B

Alternative names

Flu; Influenza A; The flu; Influenza C

Definition

The flu is a contagious infection of the nose, throat, and lungs caused by the influenza virus.

Causes, incidence, and risk factors

The flu usually begins abruptly, with a fever between 102 to 106°F (with adults on the lower end of the spectrum). Other common symptoms include a flushed face, body aches, and lack of energy. Some people have dizziness or vomiting. The fever usually lasts for a day or two, but can last 5 days.

Somewhere between day 2 and day 4 of the illness, the "whole body" symptoms begin to subside, and respiratory symptoms begin to increase. The virus can settle anywhere in the respiratory tract, producing symptoms of a cold, croup, sore throat, bronchiolitis, ear infection, or pneumonia.

The most prominent of the respiratory symptoms is usually a dry, hacking cough. Most people also develop a sore (red) throat and a headache. Nasal discharge and sneezing are common. These symptoms (except the cough) usually disappear within 4-7 days. Sometimes there's a second wave of fever at this time. Cough and tiredness usually last for weeks after the rest of the illness is over.

The most common way to catch the flu is by inhaling droplets from coughs or sneezes. Less often, it is spread when you touch a surface such as a faucet handle or phone that has the virus on it, and then touch your own mouth, nose, or eyes.

Symptoms appear 1-7 days later (usually with 2-3 days). Because the flu is airborne and very contagious, with a short incubation period, it often slams into a community all at once. This creates a cluster of school and work absences. The flu usually arrives in the winter months. Within 2 or 3 weeks of its arrival in a school, much of the classroom has had it.

Tens of millions of people in the United States get the flu each year. Most recover within a week or two, but about 114,000 people each year get sick enough to be hospitalized, and about 36,000 people die each year from the flu.

Anyone at any age can have serious complications from the flu, but those at highest risk include:

• People over 50 years of age
  
• Children 6-23 months
  
• Women more than 3 months pregnant during the flu season
  
• Anyone living in a long-term care facility
  
• Anyone with chronic heart, lung, or kidney conditions, diabetes, or weakened immune system
  

Sometimes people confuse cold and flu, which share some of the same symptoms and occur at the same time of the year (cold and flu season). However, the two diseases are very different. Most people get a cold several times each year, and the flu only once every several years.