How contagious is swine flu? Less than the novel viruses that have caused big world outbreaks in the past, new research suggests.
If someone in your home has swine flu, your odds of catching it are about one in eight, although children are twice as susceptible as adults, the study found. It is one of the first big scientific attempts to find out how much the illness spreads in homes versus at work or school, and who is most at risk.
The study was done by outbreak specialists from Imperial College London and from the U.S. Centers for Disease Control and Prevention. Results are in the current New England Journal of Medicine.
Swine flu has sickened an estimated one-sixth of Americans since the novel virus was identified in April. The second wave of cases now seems to have peaked, and health experts don't know if another surge lies ahead.
People with swine flu are advised to stay home for at least a day after their fever goes away by itself to avoid spreading illness. That puts family members at risk, but who is vulnerable and to what extent has not been known.
About 60 percent of swine flu cases have been in children, but researchers wondered: are they truly more likely to get swine flu, or just more likely to be taken to a doctor and tested for it? Are they more likely to spread the virus than adults are?
To find out, researchers studied infection patterns in 216 people with swine flu from around the United States (half of them children) and 600 people living with them.
Respiratory illnesses that researchers assumed were swine flu developed in 78 of the 600 household members, or 13 percent. However, 10 percent had symptoms more specific to flu.
That's less than the "spread" rate during earlier flu pandemics in 1957 and 1968, when 14 percent to 20 percent of household members were infected. Less is known about spread in the 1918 pandemic, but households and lifestyles were very different then. In an ordinary flu season, the virus spreads to 5 percent to 40 percent of household members, various studies have shown.