Swine influenza (H1N1 flu)

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at May 31, 2016
StartDiseasesSwine influenza (H1N1 flu)

Swine influenza (H1N1 flu) or swine flu is a highly contagious infection of the human respiratory system caused by influenza A virus subtype H1N1 virus. In 2009, this strain of flu swept across the globe causing a pandemic that lasted until the following year but mutated to become a commonly circulated seasonal flu. Due to frequent mutations that the virus has undergone, it is sometimes referred to as the 2009 H1N1 virus.


Definition & Facts

The H1N1 virus was deemed ‘swine flu’ due to the fact that it was originally found in pigs. This strain of the virus could be passed from animal to human but only rarely; those that contracted it were people who had regular, direct contact with the animals.

Eventually the virus strain mutated into a form that was transmitted from human to human and which caused the pandemic of 2009. Currently, as in 2009, the swine flu H1N1 virus can only be transmitted between people and cannot be transferred by ingesting pork products.

The swine flu pandemic of 2009 was declared to be over in 2010 by the World Health Organization after killing over 200,000 people worldwide, though an outbreak of swine flu caused by a mutated strain of H1N1 occurred in India in 2015 that killed over 1,000 people and sickened over 30,000.

Symptoms & Complaints

The symptoms of swine flu are identical to those of flus caused by other virus strains. Those afflicted will suffer from a fever of 100 °F (37.8°C) or higher. This fever is most often accompanied by a dry cough, sore throat, chills, and a stuffy nose or runny nose.

Other symptoms may include body aches, headaches, and an overall sense of exhaustion. Those suffering from swine flu are more likely to feel nauseous and experience vomiting than those afflicted with seasonal flu.

Though not as common, some patients have complained of diarrhea and the appearance of a rash. Patients that develop severe respiratory issues like shortness of breath are at a heightened risk of developing pneumonia or other major respiratory problems. Those with chronic illnesses such as asthma or diabetes are at an increased risk for developing complications. 


Swine flu of 2009 was caused by the H1N1 influenza strain. This particular strain was responsible for the outbreak in 2009. Most humans did not have a natural immunity for this strain when the pandemic occurred in 2009.

The 2009 H1N1 virus was transmitted in the same way that seasonal flu is spread between individuals: via droplets of infected secretions that travel through the air or are left on surfaces when a person coughs or sneezes. A simple sneeze can spread the virus. Contact with contaminated surfaces can result in infection.

Once inside the body, the virus takes hold in the lining of the nose, throat, and lungs. The incubation period for swine flu runs between one and four days. The contagious period begins around one day before symptoms begin to appear and can last five to seven days, though this contagiousness may last longer for children and those with weakened immune systems.

Diagnosis & Tests

In determining the presence of swine flu, a primary care physician will begin by discussing with the patient their medical history paying close attention to whether or not they have been in proximity to an individual that has been diagnosed with the H1N1 virus. Because the symptoms of swine flu are identical to those from other flu virus strains, the only way to conclusively determine the presence of swine flu is through lab testing.

A respiratory sample is taken by running a swab either around the inside of the nose or around the back of the throat. It is then sent to a specialized laboratory where antigens present in the sample are compared with known antigens in the swine flu virus. A rapid influenza diagnostic test that can be conducted at the doctor’s office is not able to diagnose whether the strain is swine flu.

Treatment & Therapy

Patients should get a good amount of rest to allow the immune system to concentrate on fighting the virus. It is also important to drink plenty of water to hold off dehydration. Over-the-counter medicines can help to relieve head and body aches and to help control fever. Patients with shortness of breath will need to have some sort of support such as a nebulizer to control the symptoms. Symptoms usually begin to let up within three to seven days.

Some doctors may prescribe patients antiviral drugs like Tamiflu® or Relenza® to combat the illness. These drugs work best when the patient receives them within 48 hours of the onset of symptoms, but can still provide relief if taken after that period. Due to the fact that viruses can mutate and develop a resistance to drugs, doctors usually reserve use of these drugs for those at a high risk for complications. Antibiotics may be prescribed if the patient develops pneumonia, but not to directly combat the flu. This is because swine flu is caused by a virus, not bacteria.

Severe cases most of the time require additional support from specialists. It is not typically necessary to seek medical treatment if the patient is in good health and has mild symptoms; however, those who are pregnant or suffer from chronic illness should not hesitate to be seen by a doctor. 

Prevention & Prophylaxis

Prevention of the swine flu follows the same protocol as preventing other strains of flu. People should wash their hands regularly with soap and water or use an alcohol-based hand sanitizer. They should avoid touching the eyes, nose and mouth areas so as not to transfer germs.

The swine flu virus can linger on household surfaces, so it is important to disinfect them often. Those who are showing symptoms of the flu should stay home to avoid spreading the virus, and people should stay away from anybody showing flu symptoms. During the flu season, it may be helpful to avoid large gatherings.

One of the best ways to reduce the chance of becoming infected is to get the seasonal influenza vaccines which comes in both an injectable shot and a nasal spray and includes protection from the swine flu virus.