Swine flu is a highly contagious respiratory disease in pigs. The disease is caused by a virus and causes sickness in the animals, but has a low death rate. The virus frequently circulates among the animals throughout the year, with outbreaks more common in the fall and winter.
How do people become infected?
The CDC says the spread of swine flu can occur in two ways: through contact with infected pigs or environments contaminated with the virus; or through contact with a person with swine flu. The CDC has determined that the virus is contagious and spreading among people, but at this time it is not known how easily that happens.
Is this a pandemic?
No, not yet, at least. But it is considered an outbreak, or a sudden increase in the numbers of a particular illness. What caused doctors in Mexico to sit up and take notice was a sudden jump in serious pneumonias at the end of the regular flu season. Tests are under way now to determine how many of these cases might be swine flu.
A pandemic is a worldwide outbreak of disease, typically affecting millions of people. An epidemic is a disease that spreads rapidly and widely in a localized region or country. And since officials aren't sure how many of the cases are actually swine flu, it's still too early to call it an epidemic.
The World Health Organization, one of the groups monitoring the situation and coordinating an international response to the swine flu outbreak, currently has the situation listed as "Phase 3," on a six-step scale, which means that though the disease has affected small clusters of people, the swine flu "has not resulted in human-to-human transmission sufficient to sustain community-level outbreaks."
WHO officials have called the outbreak a "public health emergency of international concern," but have so far held off raising the pandemic level any higher. Phases 4 and higher represent significant human-to-human spread of the virus both at a community level and worldwide.
If this isn't yet a pandemic, why the alarm?
Officials don't yet know how contagious the disease is or exactly how it's spreading, but the high number of cases as well as the geographic distribution has them on the lookout for more cases, which are expected to be found. Influenza viruses, like the swine flu, can be transmitted between people by coughing or sneezing, or by touching something with a flu virus on it.