(CNN)Here's a look at the H1N1 influenza virus, also known as swine flu. There was a pandemic outbreak across the globe which lasted from 2009 to 2010.
Human cases of H1N1 from April 2009-April 2010
Fatalities in the United States - Estimated total is 12,469.
Fatalities Worldwide - A 2012 study estimated a range between 151,700 and 575,400 deaths.
Swine flu is a respiratory disease caused by type A influenza virus in pigs. Swine flu outbreaks are common in pig herds, but generally the disease causes few deaths in pigs.
Swine flu is transmitted between pigs through close contact and contact with contaminated objects. Flu spreads when someone touches an object coughed or sneezed on by an infected person and then touches his/her mouth or nose. However, swine flu cannot be passed from properly handled pork products to humans.
Swine flu outbreaks in pigs can occur at any time, but mostly occur during the late fall and winter months.
It is a constantly mutating virus. Pigs are susceptible to viruses from birds, humans and other swine. When different influenza viruses strike pigs, the genes can mutate and new viruses can develop.
In pigs, there are currently three common influenza A virus subtypes in the United States: H1N1, H1N2 and H3N2.
Swine Flu in Humans
Swine flu occurs in people that are in contact with infected pigs. When this occurs, it is called a "variant influenza virus."
Symptoms are similar to that of regular human influenza and can include fever, lethargy, lack of appetite, coughing, runny nose, sore throat, nausea, vomiting and diarrhea.