Also known as influenza
Elizabeth Molina Ortiz, MD, MPH, is a board-certified specialist in family medicine and is the former medical director of a community health center.
The flu is a highly contagious illness caused by influenza viruses that infect the respiratory tract (nose, throat, and lungs). Symptoms of the flu, including fever, sore throat, body aches, and cough, tend to come on suddenly. Most people recover from the flu within two weeks. However, young children, the elderly, and those with serious medical conditions can develop complications such as pneumonia.
The incubation period is the time between exposure to an infection and the first appearance of symptoms. The incubation period for influenza is between one and four days after exposure.
Influenza A is the most common type of influenza virus that causes the seasonal flu. Influenza A viruses are classified by subtypes based on surface proteins hemagglutinin (H) and neuraminidase (N). The viruses are named for the combination of proteins, such as A(H1N1) or A(H3N2).
Influenza B is the second most common type of influenza virus that causes the seasonal flu. Influenza B viruses are classified by subtypes based on lineage as B/Yamagata or B/Victoria.
Polymerase chain reaction (PCR) testing is a laboratory technique that produces millions of copies of a short segment of DNA until there is enough for analysis and detection. PCR testing is a diagnostic tool used to detect infections including influenza, coronavirus, HIV, hepatitis, and salmonella. It is also used to diagnose cancer, central nervous system diseases, and autoimmune diseases.
Vaccines are used to boost immunity against serious infectious diseases. Also called inoculation, a vaccine introduces a small piece of virus that is changed or killed so it can’t cause disease. The immune system produces antibodies against the pathogen, helping to fight against infection if you are exposed to it later. You may still catch the illness, but it will likely be a milder infection.
A viral infection is an infection caused by a virus. Viruses are microscopic organisms that can be transmitted from person to person. Some viruses, like the common cold, influenza, and COVID-19, can cause upper respiratory infection, while enteroviruses commonly cause vomiting and diarrhea.
Symptoms of the flu tend to come on suddenly over the course of a few hours and commonly last for four to five days. However, some people may recover from the flu in as few as two days or as many as seven or more days.
Influenza is contagious from before you even start to feel symptoms and continues for several days. On average, people are contagious 24 hours before symptoms appear for up to about five days after becoming ill.
Symptoms of influenza include fever, chills, headache, body aches, runny nose, sore throat, cough, and fatigue. Symptoms tend to come on quickly over the course of a few hours.
You can catch the influenza at any time of year, but it is most prominent in the fall and winter in the United States. Flu season typically spans from October through April with peak cases between December and March, although flu activity can last as late as May.
Fever is a common symptom with influenza. Part of the body’s defenses against the virus, an increased body temperature helps to prevent the virus from replicating. However, not everyone will experience a fever when they have the flu.
Influenza is passed from person to person through infected respiratory droplets shared via sneezing, coughing, talking, or blowing one’s nose. It can also be transmitted via contact with contaminated surfaces. The best way to prevent contracting the flu is to avoid close contact with people who are sick, wash your hands frequently, and get an annual flu shot.
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