H1N1 Influenza

H1N1 influenza, commonly known as swine flu, is a respiratory infection caused by a type A influenza virus that can spread quickly from person to person and cause symptoms ranging from mild flu-like illness to severe complications.

Table of contents

• What is H1N1 influenza?
• How H1N1 spreads
• Signs and symptoms
• The 2009 H1N1 pandemic
• How H1N1 is diagnosed
• Treatment options
• Preventing H1N1 infection
• People at higher risk

What is H1N1 influenza?

H1N1 influenza is an infectious viral illness that causes respiratory tract infections in humans. It is called swine flu because it resembles a respiratory infection that affects pigs, though the virus changed over time to infect humans^[2]. The name comes from the combination of two proteins found in the virus: hemagglutinin (the H protein) and neuraminidase (the N protein), which help the virus attach to and enter cells in your body^[4].

H1N1 is a subtype of influenza A virus that causes both upper and, in some cases, lower respiratory tract infections^[3]. The virus leads to a lung disease in pigs, but in humans it appears as a respiratory infection similar to seasonal flu^[2].

Today, H1N1 is considered one of the regular seasonal flu viruses. It is included in the annual flu vaccine along with other influenza strains^[1][2]. While most people recover on their own, the flu and its complications can be deadly, especially for people at high risk^[1].

How H1N1 spreads

H1N1 influenza spreads from person to person and is highly contagious^[2][8]. When someone with the flu coughs or sneezes, tiny droplets containing the virus go into the air. You can become infected when you breathe in these droplets^[2]. You can also catch the virus by touching a surface that has the virus on it, such as a doorknob or counter, and then touching your mouth, nose, or eyes^[2].

It is important to know that you cannot get H1N1 by eating pork or other pork products. The virus is killed when pork is cooked properly at temperatures of 70 degrees Celsius^[2][14].

The virus can spread quickly, especially indoors^[14]. An infected person can spread the virus to others from the first day of infection up to seven days after symptoms begin^[8]. Symptoms typically develop about one to four days after exposure to the virus^[1], though some sources indicate symptoms may start three to five days after exposure^[2][8].

Signs and symptoms

The symptoms of H1N1 flu are similar to those of regular seasonal flu^[1][2]. Symptoms usually start quickly and can include^[1]:

• Fever, often sudden and sometimes reaching above 39 degrees Celsius, though not everyone develops fever
• Cough, which may be frequent and severe
• Sore throat
• Runny or stuffy nose
• Body aches and muscle pain
• Headache
• Chills and sweats
• Tiredness and weakness
• Loss of appetite
• Eye symptoms such as watery, red eyes or eye pain
• Digestive symptoms like nausea, vomiting, or diarrhea, though these are more common in children than adults

Most people with H1N1 will gradually improve and recover within four to seven days^[8]. However, coughing may last for another one or two weeks after other symptoms have gone^[20].

Some symptoms require immediate medical attention. Parents should call a healthcare provider right away if their baby or child has trouble breathing, trouble waking up, is not drinking enough fluids, has a fever with rash, or shows confusion^[2].

Rarely, H1N1 can lead to serious complications such as acute respiratory distress syndrome (a severe lung condition where the lungs cannot provide enough oxygen to the body), secondary bacterial infections, severe pneumonia, shortness of breath, rapid breathing, respiratory failure, seizures, and death^[3][8].

The 2009 H1N1 pandemic

In April 2009, researchers discovered a new strain of H1N1 virus. It was first detected in the United States and then spread rapidly around the world^[2][6]. This new virus spread quickly because it was a type of flu virus that people had not been exposed to before. Young people were not immune to the new virus, though older people appeared to have some immunity, possibly from exposure to an older strain of H1N1^[2].

The 2009 H1N1 virus gained worldwide attention and was often called swine flu. During the 2009-10 flu season, this new H1N1 virus was a new combination of influenza viruses that normally infect pigs, birds, and humans^[1]. The World Health Organization declared H1N1 flu to be a pandemic in June 2009^[1][6]. The virus caused an estimated 284,400 deaths worldwide in that year^[1]. At least 150,000 people died globally, and eighty percent of those who died were younger than 65 years old^[2].

The World Health Organization declared the pandemic over in August 2010^[1][2][6]. However, the H1N1 flu strain from the pandemic became one of the strains that cause seasonal flu. People can still get and spread H1N1, and it can cause illness, hospitalization, and death^[2].

It is important to note that the 2009 H1N1 pandemic is different from the 1918 Spanish flu pandemic, though both were caused by H1N1 viruses. In 1918, an H1N1 flu pandemic infected 500 million people around the world and at least 50 million people died^[2].

How H1N1 is diagnosed

A healthcare provider can diagnose H1N1 influenza by performing a physical exam and asking about your symptoms^[2][9]. Your provider may also review your symptoms with you over the phone^[9].

Your healthcare provider may order a test to find influenza viruses such as H1N1. There are many tests used to diagnose influenza, including a rapid flu test that checks for several different flu viruses^[2][9]. However, not everyone who has the flu needs to be tested. In most cases, knowing that someone has the flu does not change the treatment plan^[9].

To diagnose H1N1, a sample from the respiratory tract should generally be collected within the first four to five days of illness, when an infected person is most likely to spread the virus^[14]. It may take a few days to get the H1N1 test results back^[2].

Healthcare providers are more likely to use a test to diagnose flu if you are already in the hospital, at high risk of complications from the flu, live with someone who is at greater risk of flu complications, or if they need to determine whether another condition is causing your symptoms^[9].

Treatment options

Most people with H1N1 who are otherwise healthy do not need special drugs or treatments^[2][9]. Treatment is largely supportive and focuses on relieving symptoms. If you have swine flu, you should^[2][9][12]:

• Get plenty of rest
• Drink lots of fluids, including water, warm soup, and drinks that contain minerals
• Eat a light diet
• Stay home from work, school, and other public places for at least 24 hours after your fever is gone without using fever-reducing medicine
• Take pain relievers like acetaminophen (Tylenol) or ibuprofen (Advil, Motrin IB) to reduce fever and relieve aches and pains

It is very important not to give products containing aspirin to children or teens recovering from flu-like symptoms. Aspirin has been linked to Reye’s syndrome, a rare but potentially life-threatening condition in children^[9][14].

If you are very ill or have underlying medical conditions, your healthcare provider may prescribe an antiviral medicine. Antiviral drugs such as oseltamivir (Tamiflu) or zanamivir (Relenza) can kill the virus^[2][9][11]. These drugs can shorten the time you are sick and help ease your symptoms. Antiviral drugs work best if you start taking them when your symptoms begin, ideally within the first day or two of illness^[2][9]. Early antiviral treatment within 72 hours of symptom onset may decrease severe disease and reduce the risk of death^[3].

Patients with severe illness or those who are at high risk of complications should be treated with antiviral medications as soon as possible, without waiting for the results of laboratory tests^[16].

Preventing H1N1 infection

The best way to reduce the risk of H1N1 flu is to get vaccinated each year. The seasonal flu vaccine now includes protection against the H1N1 flu strain along with other seasonal flu viruses^[1][12]. Vaccination and other preventive measures are critical in reducing H1N1 influenza transmission during outbreaks^[3].

There are several actions you can take to protect yourself and others from H1N1^[2][14][17]:

• Wash your hands often with soap and water. If soap and water are not available, use an alcohol-based hand cleaner that contains at least 60 percent alcohol
• Avoid touching your eyes, nose, or mouth, as germs spread this way
• Cover your nose and mouth with a tissue when you cough or sneeze, and throw the tissue in the trash after you use it
• Avoid close contact with people who are sick
• Keep your work areas and home clean, and ventilate closed areas
• If you are sick, stay home and keep your distance from others to protect them from getting sick
• Wearing a mask can help prevent the spread of the virus when you are within six feet of others

If you develop sudden high fever along with cough, headache, and muscle and joint pain, see your doctor^[14]. When you are sick, stay home for at least 24 hours after your fever is gone without using fever-reducing medication^[17].

People at higher risk

While H1N1 can be mild in many people, it can cause serious and sometimes life-threatening complications in certain groups. People at higher risk of developing serious flu complications include^[11][14]:

• Young children, especially those under five years of age and particularly those under two years
• Adults 65 years of age and older
• Pregnant women
• People with weakened immune systems
• People with chronic medical conditions such as heart disease, diabetes, and asthma
• People who are morbidly obese
• Residents of long-term care facilities, including nursing homes

If people in these high-risk groups develop flu-like symptoms, it is best for them to contact their doctor as soon as possible. Their doctor may prescribe antiviral drugs that can treat the flu, and these drugs work better when started early^[11].

Most influenza deaths occur in people at higher risk of complications. During the 2009 pandemic, eighty percent of those who died were younger than 65, which was unusual compared to typical seasonal flu patterns^[2].