What is H1N1 (swine) flu?

H1N1 (referred to as "swine flu" early on) is a new influenza virus causing illness in people. This new virus was first detected in people in the United States in April 2009. Other countries, including Mexico and Canada, have also reported people sick with this new virus. This virus is spreading from person-to-person, probably in much the same way that regular seasonal influenza viruses spread.
In late March and early April 2009, cases of human infection with swine influenza A (H1N1) viruses were first reported in Southern California and near San Antonio, Texas.
In the beginning it was difficult to predict the effect of this virus on general population. In seasonal flu, there are certain people who are at higher risk of serious flu-related complications. This includes people with 65 years of more age, children below five years, pregnant women, and people of any age with chronic medical conditions.
This virus is contagious but, at this time, it not known how easily the virus spreads between people. The symptoms of H1N1 swine flu in people are similar to the symptoms of regular human flu and include fever, cough, sore throat, body aches, headache, chills and fatigue. Some people have reported diarrhoea and vomiting associated with H1N1 swine flu. Severe illness (pneumonia and respiratory failure) and even deaths have been reported with H1N1 swine flu infection. Like seasonal flu, H1N1 swine flu may cause a worsening of underlying chronic diseases.

In children, emergency warning signs that need urgent medical attention include:

Fast breathing or difficulty in breathing
Bluish or gray skin colour
Not drinking enough fluids
Severe or persistent vomiting
Not waking up or not interacting
Being so irritable that the child does not want to be held
Flu-like symptoms improve but then return with fever and worse cough

In adults, emergency warning signs that need urgent medical attention include:

Difficulty in breathing or shortness of breath
Pain or pressure in the chest or abdomen
Sudden dizziness
Confusion
Severe or persistent vomiting
Flu-like symptoms improve but then return with fever and worse cough