Flu Season 2020: What is this contagious respiratory illness? Here are the symptoms and how it spreads

An infectious respiratory disease caused by influenza viruses, it is thought to spread mainly by droplets made when people with flu cough, sneeze or talk

                            Flu Season 2020: What is this contagious respiratory illness? Here are the symptoms and how it spreads
(Getty Images)

Flu is an infectious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs. It can cause mild to severe illness, and can also lead to death at times. Serious outcomes of flu infection can result in hospitalization or death.  

Types of influenza viruses

There are four types of influenza viruses: A, B, C, and D. Human influenza A and B viruses cause seasonal epidemics of disease (known as the flu season) almost every winter in the US. “The influenza A and B viruses that routinely spread in people (human influenza viruses) are responsible for seasonal flu epidemics each year,” says the US Centers for Disease Control and Prevention (CDC). 

Influenza A viruses are the only influenza viruses known to cause flu pandemics, that is the global epidemics of flu disease. A pandemic can occur when a new and very different influenza A virus emerges that both infect people and can spread efficiently between people. Influenza type C infections generally cause mild illness and are not thought to cause human flu epidemics. Influenza D viruses primarily affect cattle and are not known to infect or cause illness in people.

The influenza A and B viruses that routinely spread in people are responsible for seasonal flu epidemics each year. (Getty Images)


Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: hemagglutinin (H) and neuraminidase (N). While there are potentially 198 different influenza A subtype combinations, only 131 subtypes have been detected in nature. “Current subtypes of influenza A viruses that routinely circulate in people include: A(H1N1) and A(H3N2),” explain experts. The influenza A (H1N1) virus that emerged in 2009 caused the first global influenza pandemic in more than 40 years. 

Flu symptoms

People who have the flu often feel some or all of these symptoms, which include fever or feeling feverish/chills, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, and fatigue or tiredness. Some people may have vomiting and diarrhea, though this is more common in children than adults. People may be sick with the flu and have respiratory symptoms without a fever. The time from when a person is exposed and infected with flu to when symptoms begin is about two days, but it can range from about one to 4 days. 

Flu viruses usually cause the most illness during the colder months of the year. However, influenza can also occur outside of the typical flu season. Other viruses can also cause respiratory illness similar to the flu. “So, it is impossible to tell for sure if you have the flu based on symptoms alone. If your doctor needs to know for sure whether you are sick with the flu, there are laboratory tests that can be done,” emphasizes the CDC.

Emergency warning signs of flu. (CDC)

Flu is different from a cold. Flu usually comes on suddenly. “Flu and the common cold are both respiratory illnesses but they are caused by different viruses. Because these two types of illnesses have similar symptoms, it can be difficult to tell the difference between them based on symptoms alone. In general, flu is worse than the common cold, and symptoms are more intense. Colds are usually milder than flu. People with colds are more likely to have a runny or stuffy nose. Colds generally do not result in serious health problems, such as pneumonia, bacterial infections, or hospitalizations. Flu can have very serious associated complications,” explains the agency. 

Cold versus the flu. (CDC)

How does the flu spread?

Flu viruses are thought to spread mainly from person to person through droplets made when people with flu cough, sneeze or talk. People with flu can spread it to others up to about 6 feet away. Less often, a person might get the flu by touching a surface or object that has the flu virus on it and then touching their mouth, nose, or possibly their eyes.

People with flu are most contagious in the first 3-4 days after their illness begins. People infected with the flu may be able to infect others beginning one day before symptoms develop and up to 5-7 days after becoming sick. This implies that people may be able to spread the flu to someone else before they know they are sick as well as while they are sick.  Young children, those who are severely ill, and those who have severely weakened immune systems may be able to infect others for longer than 5-7 days. 

Influenza A viruses are found in many different animals, including ducks, chickens, pigs, whales, horses, seals, and cats. Influenza B viruses circulate widely only among humans. According to the CDC, while it is unusual for people to get influenza infections directly from animals, sporadic human infections and outbreaks caused by certain avian influenza A viruses have been reported. 

Are there any tests and treatments?

While multiple tests are available, “rapid influenza diagnostic tests (RIDTs)” are the most common. They work by detecting the parts of the virus (antigens) that stimulate an immune response. They can provide results within about 10-15 minutes, but are not considered to be as accurate as other flu tests. “Therefore, you could still have the flu, even though your rapid test result is negative. Other flu tests are called “rapid molecular assays” that detect the genetic material of the virus. Rapid molecular assays produce results in 15-20 minutes and are more accurate than RIDTs,” the CDC explains. 

Several more accurate and sensitive flu tests are available that are performed in specialized laboratories, such as those found in hospitals or state public health laboratories. They need a healthcare provider to swipe the inside of the nose or the back of the throat with a swab and then send the swab for testing. Results may take one to several hours. 

Most people with the flu have mild illness and do not need medical care or antiviral drugs. Health experts, however, advise that if a person belongs to a high-risk group or is very sick or worried about the illness, they should contact their healthcare provider. There are drugs the doctor may prescribe for treating the flu called ‘antivirals.’ These drugs can lessen symptoms and shorten the time a person is sick by one or two days, and they may also prevent serious flu complications, like pneumonia.

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