What is H1N1 (swine flu)?
According to the Centers for Disease Control and Prevention (CDC), the 2009 H1N1 (referred to as "swine flu") is a new influenza virus causing illness in people. This new virus was first detected in people in the United States in April 2009. This virus is spread by person-to-person contact worldwide, the same way that regular seasonal influenza viruses spread. On June 11, 2009, the World Health Organization (WHO)
signaled that a pandemic of 2009 H1N1 flu was underway. This virus was originally referred to as "swine flu" because laboratory testing showed that many of the genes in this new virus were very similar to influenza viruses that normally occur in pigs (swine) in North America.1
How does H1N1 compare to the seasonal flu in terms of its severity and infection rates?
With seasonal flu, we know that seasons vary in terms of timing, duration, and severity. Seasonal influenza can cause mild to severe illness, and at times can lead to death. Each year, in the United States, on average, 36,000 people die from flu-related complications, and more than 200,000 people are hospitalized from flu-related causes. Of those hospitalized, 20,000 are children younger than 5 years old. More than 90% of deaths and about 60% of hospitalizations occur in people older than 65.
When the 2009 H1N1 outbreak was first detected in mid-April 2009, the CDC began working with states to collect, compile, and analyze information regarding the 2009 H1N1 flu outbreak, including the numbers of confirmed and probable cases and the ages of these people. The information analyzed by the CDC supports the conclusion that 2009 H1N1 flu has caused greater disease burden in people younger than 25 years of age than in older people. At this time, there are few cases and few deaths reported in people older than 64 years old, which is unusual when compared with seasonal flu. However, pregnancy and other previously recognized high-risk medical conditions from seasonal influenza appear to be associated with increased risk of complications from this 2009 H1N1. These underlying conditions include asthma, diabetes, suppressed immune systems, heart disease, kidney disease, neurocognitive and neuromuscular disorders, and pregnancy.1