Swine flu has sickened an estimated one-sixth of Americans since the novel virus was first identified in April. The second wave of cases now seems to have peaked, and health specialists do not know if another surge lies ahead.
To avoid spreading illness, people with swine flu are advised to stay home for at least a day after their fever goes away by itself. 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 youngsters truly more likely to get swine flu, or just more likely to be taken to a doctor and tested for it? And 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.
Children were twice as susceptible to catching swine flu as adults were, and even more so if they were younger than 4, said one of the researchers, Lyn Finelli, of the CDC’s flu division.
“It fits with what I’m seeing clinically,’’ said Dr. James King, of the American Academy of Family Physicians’ board of directors and a doctor in Tennessee.
Nearly three-fourths of households in the study managed to avoid spreading the illness to any family members.
In homes where the germ was transmitted, researchers found something unexpected: “People at all ages were just as likely to spread the virus,’’ Finelli said. “That was surprising, since we always think of kids as super-spreaders.’’
The study was funded by public and private health-related groups in England and the United States.
