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Jai Ganesh

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Influenza

Influenza

Gist

Understanding Influenza: 

Flu is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs. It can cause mild to severe illness, and at times can lead to death. The best way to prevent flu is by getting a flu vaccine each year.

The flu is caused by an influenza virus. Most people get the flu when they breathe in tiny airborne droplets from the coughs or sneezes of someone who has the flu. You can also catch the flu if you touch something with the virus on it, and then touch your mouth, nose, or eyes. People often confuse colds and flu.

Summary

* Flu is a contagious respiratory illness caused by influenza viruses
* Flu can cause mild to severe illness
* Most experts believe that flu viruses spread mainly by tiny droplets made when people with flu cough, sneeze, or talk
* The first and most important step inpreventing flu is to get a flu vaccine each year.

Understanding Influenza

Flu is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs. It can cause mild to severe illness, and at times can lead to death. The best way to prevent flu is by getting a flu vaccine each year.

Symptoms

Flu can cause mild to severe illness, and at times can lead to death. Flu symptoms usually come on suddenly. People who have flu often feel some or all of these signs and symptoms:

* fever* or feeling feverish/chills
* cough
* sore throat
* runny or stuffy nose
* muscle or body aches
* headaches
* fatigue (tiredness)
* some people may have vomiting and diarrhea, though this is more common in children than adults.

(*It's important to note that not everyone with flu will have a fever.)

Not everyone with flu has symptoms

Some people with influenza virus infections do not develop any symptoms at all. A household study conducted during the 2017-2023 flu seasons found that 8 percent of people who tested positive for flu did not have symptoms.

Period of Contagiousness

You may be able to spread flu to someone else before you know you are sick, as well as when you are sick with symptoms.

* People with flu are most contagious during the first three days of their illness.
* Some otherwise healthy adults may be able to infect others beginning one day before symptoms develop and up to five to seven days after becoming sick.
* Some people, including young children and people with weakened immune systems, may be contagious for longer periods of time.

Onset of Symptoms

The time from when a person is exposed and infected with influenza virus to when symptoms begin is about two days but can range from about one to four days.

People at risk

Anyone can get flu (including healthy people), and serious problems related to flu can happen at any age, but some people are at higher risk of developing serious flu-related complications if they get sick. This includes people 65 years and older, people of any age with certain chronic medical conditions (such as asthma, diabetes, or heart disease),people with a body mass index (BMI) of 40 kg/m^2or higher, those who are pregnant, and children younger than five years.

How it spreads

Most experts believe that flu viruses spread mainly by tiny droplets made when people with flu cough, sneeze, or talk. These droplets can land in the mouths or noses of people who are nearby. Less often, a person might get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose or possibly their eyes.

Prevention

The first and most important step inpreventing flu is to get a flu vaccine each year. Flu vaccine has been shown to reduce flu-related illnesses and the risk of serious flu complications that can result in hospitalization or even death. CDC also recommends everyday preventive actions (like staying away from people who are sick (distancing), covering coughs and sneezes, frequent handwashing, and taking steps for cleaner air) to help slow the spread of germs that cause respiratory (nose, throat, and lungs) illnesses like flu. More information is available about core and additional prevention strategies.

Details

The flu is a common respiratory illness you get from the influenza virus. Symptoms often include fever, head and body aches, coughing and a stuffy or runny nose. You’re at risk for serious complications if you have an underlying health condition or are pregnant. Getting vaccinated every year is the best way to avoid getting sick with the flu.

Overview

What is the flu (influenza)?

The flu is an illness you get from the influenza virus. It causes symptoms like head and body aches, sore throat, fever and respiratory symptoms, which can be severe. Flu is most common in winter months, when many people can get sick at once (an epidemic).

When is flu season?

Flu season — when cases of the flu go up dramatically — in the Northern Hemisphere (which includes the U.S.) is October through May. The highest number of cases (peak) usually happen between December and February.

How common is the flu?

The flu is one of the most common infectious diseases. Every flu season, about 20 to 40 million people in the U.S. catch the flu.

What is the difference between the flu and the common cold?

The flu and the common cold can have similar symptoms, like runny nose and cough. But cold symptoms are usually mild and flu symptoms can be severe and lead to serious complications. Different viruses cause colds and the flu.

How do I know if I have the flu or COVID-19?

Since they have similar symptoms, the only way to know for sure if you have the flu or COVID-19 is to get tested. They both have a risk of serious illness. But different viruses cause these infections, and providers treat them with different medications.

Who is at higher risk for complications from the flu?

Certain health conditions can put you at higher risk for severe illness from the flu. This includes life-threatening complications that require hospitalization. You’re at higher risk for serious illness if you:

* Have asthma, COPD or another chronic lung disease.
* Have a history of kidney, liver, neurological, heart or blood vessels disease, including stroke.
* Have a condition that causes issues with muscle function or makes it difficult to cough, swallow or clear fluids from your airways.
* Have diabetes.
* Have a weakened immune system (from HIV/AIDS, cancer or immunosuppressive medications).
* Have a blood disorder, like sickle cell disease.
* Have a BMI greater than 30 (have obesity).
* Are under 5 years old or over 65 years old.
* Are pregnant.
* Are under 19 years old and take aspirin regularly.
* Live in a long-term care facility.

Non-Hispanic Black people, non-Hispanic American Indians, Alaska Native people and Hispanic or Latino people have the highest rates of severe illness from the flu compared to non-Hispanic White people and non-Hispanic Asian people.

Symptoms and Causes

With so many symptoms in common, it can be hard to tell the difference between a cold and the flu. Here’s how to tell which is which.

What are the symptoms of the flu?

Symptoms of the flu usually come on quickly, and can include:

* Fever.
* Chills.
* Body aches.
* Cough.
* Headache.
* Sore throat.
* Runny or stuffy nose (congestion).
* Tiredness or feeling run down.
* Diarrhea or vomiting (usually only in kids).

You may not have all of these symptoms.

What causes the flu?

The influenza virus causes flu. Influenza A, B and C are the most common types that infect people. Influenza A and B are seasonal (most people get them in the winter) and have more severe symptoms. Influenza C doesn’t cause severe symptoms and it’s not seasonal — the number of cases stays about the same throughout the year.

H1N1 (“swine flu”) and bird flu are both subtypes of influenza A.

Is the flu contagious?

Yes, the flu is contagious (it spreads from person to person). For every person infected, they spread the flu to one to two more people.

How does the flu spread?

The influenza virus spreads from direct or indirect contact with someone else who’s infected. Common ways to get the flu include:

* From someone nearby coughing, sneezing or talking. Droplets can either get onto your hands or move through the air to get into your nose or mouth. The flu then moves into your lungs.
* By touching a surface that’s contaminated by the flu virus, then touching your face, nose, mouth or eyes. This includes things like door knobs, desks, computers and phones.
* By touching the hands or face of someone who has the flu, then touching your face, nose, mouth or eyes.

How long after exposure will I get the flu?

If infected, you’ll usually get symptoms of the flu one to four days after exposure (incubation period).

Diagnosis and Tests:

How is the flu diagnosed?

Your provider diagnoses the flu by listening to your symptoms and testing a sample of mucus from your nose. They’ll put a long stick with a soft tip (swab) in your nose to test for influenza. Results may take a few minutes or your provider may send the sample to a lab, where you’ll get results in a day or two.

Management and Treatment:

How is the flu treated?

Providers can treat the flu with antiviral medications under certain circumstances. Antivirals can reduce your risk of severe illness and shorten the amount of time you’re sick. Many people can treat the flu without prescription medications. Providers prescribe antivirals if you:

* Have had symptoms for under 48 hours. Antivirals are less likely to work if you start them after two days of symptoms. The virus has already made more copies of itself and your body has started to fight it off with its own antibodies.
* Have an underlying condition or are at risk for severe illness. Providers may prescribe antivirals even if you’ve had symptoms for longer than 48 hours.
* Have severe symptoms, even if you’ve been sick for longer than 48 hours.
* Live with or care for people who are at risk for severe complications of the flu.

Additional Information

Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptoms begin one to four (typically two) days after exposure to the virus and last for about two to eight days. Diarrhea and vomiting can occur, particularly in children. Influenza may progress to pneumonia from the virus or a subsequent bacterial infection. Other complications include acute respiratory distress syndrome, meningitis, encephalitis, and worsening of pre-existing health problems such as asthma and cardiovascular disease.

There are four types of influenza virus: types A, B, C, and D. Aquatic birds are the primary source of influenza A virus (IAV), which is also widespread in various mammals, including humans and pigs. Influenza B virus (IBV) and influenza C virus (ICV) primarily infect humans, and influenza D virus (IDV) is found in cattle and pigs. Influenza A virus and influenza B virus circulate in humans and cause seasonal epidemics, and influenza C virus causes a mild infection, primarily in children. Influenza D virus can infect humans but is not known to cause illness. In humans, influenza viruses are primarily transmitted through respiratory droplets from coughing and sneezing. Transmission through aerosols and surfaces contaminated by the virus also occur.

Frequent hand washing and covering one's mouth and nose when coughing and sneezing reduce transmission, as does wearing a mask. Annual vaccination can help to provide protection against influenza. Influenza viruses, particularly influenza A virus, evolve quickly, so flu vaccines are updated regularly to match which influenza strains are in circulation. Vaccines provide protection against influenza A virus subtypes H1N1 and H3N2 and one or two influenza B virus subtypes. Influenza infection is diagnosed with laboratory methods such as antibody or antigen tests and a polymerase chain reaction (PCR) to identify viral nucleic acid. The disease can be treated with supportive measures and, in severe cases, with antiviral drugs such as oseltamivir. In healthy individuals, influenza is typically self-limiting and rarely fatal, but it can be deadly in high-risk groups.

In a typical year, five to 15 percent of the population contracts influenza. There are 3 to 5 million severe cases annually, with up to 650,000 respiratory-related deaths globally each year. Deaths most commonly occur in high-risk groups, including young children, the elderly, and people with chronic health conditions. In temperate regions, the number of influenza cases peaks during winter, whereas in the tropics, influenza can occur year-round. Since the late 1800s, pandemic outbreaks of novel influenza strains have occurred every 10 to 50 years. Five flu pandemics have occurred since 1900: the Spanish flu from 1918 to 1920, which was the most severe; the Asian flu in 1957; the Hong Kong flu in 1968; the Russian flu in 1977; and the swine flu pandemic in 2009.

Signs and symptoms

The symptoms of influenza are similar to those of a cold, although usually more severe and less likely to include a runny nose. The time between exposure to the virus and development of symptoms (the incubation period) is one to four days, most commonly one to two days. Many infections are asymptomatic. The onset of symptoms is sudden, and initial symptoms are predominately non-specific, including fever, chills, headaches, muscle pain, malaise, loss of appetite, lack of energy, and confusion. These are usually accompanied by respiratory symptoms such as a dry cough, sore or dry throat, hoarse voice, and a stuffy or runny nose. Coughing is the most common symptom. Gastrointestinal symptoms may also occur, including nausea, vomiting, diarrhea, and gastroenteritis, especially in children. The standard influenza symptoms typically last for two to eight days. Some studies suggest influenza can cause long-lasting symptoms in a similar way to long COVID.

Symptomatic infections are usually mild and limited to the upper respiratory tract, but progression to pneumonia is relatively common. Pneumonia may be caused by the primary viral infection or a secondary bacterial infection. Primary pneumonia is characterized by rapid progression of fever, cough, labored breathing, and low oxygen levels that cause bluish skin. It is especially common among those who have an underlying cardiovascular disease such as rheumatic heart disease. Secondary pneumonia typically has a period of improvement in symptoms for one to three weeks followed by recurrent fever, sputum production, and fluid buildup in the lungs, but can also occur just a few days after influenza symptoms appear. About a third of primary pneumonia cases are followed by secondary pneumonia, which is most frequently caused by the bacteria Streptococcus pneumoniae and Staphylococcus aureus.

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