Under age 18 twice as likely to get H1N1 flu from family member

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A new analysis shows that household members under age 18 are more likely to get H1N1 flu from a family member, compared to adults. Adults over age 50 are less susceptible to contracting the flu. The new findings also show that, contrary to previous thoughts, younger people are not more likely to spread H1N1 flu.

For the study scientists at the MRC Centre for Outbreak Analysis & Modelling at Imperial College London and the US Centers for Disease Control and Prevention (CDC) looked at data from the CDC, analyzing the behavior of pandemic flu among 216 individuals thought to have H1N1, and 600 household members.

The scientists found that youth (under age 18) were twice as likely to contract flu from a family member, compared to age 19 to 50, and those over age 50 were least susceptible to H1N1 infection.

Dr Simon Cauchemez, lead author of the paper from the MRC Centre for Outbreak Analysis and Modelling at Imperial College London, said: "At the start of the current flu pandemic we didn't know how different factors affected the risk of transmitting the virus to other people. If we are advising people to stay at home if they develop flu-like symptoms, we need to understand the implications this might have for other household members. Our new research helps us to do this – for example it shows that children are more at risk of being infected than adults.”

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Dr. Cauchemez also supported CDC guidelines, saying, if it is “only likely to transmit the virus to other people for the first few days of their illness, keeping people off work for a week may be unnecessary and could be detrimental to the economy. In view of this, the new CDC guidelines are very sensible.” The CDC previously recommended staying home for 7 days after being infected with flu, but the new recommendations states “people with influenza-like illness remain at home until at least 24 hours after they are free of fever (100° F [37.8°C]), or signs of a fever without the use of fever-reducing medications.”

The study also showed that H1N1 flu is spread just before or at the very beginning of signs of infection. Interestingly, spread of flu was lower in households with more members. The researchers believe larger households have less contact with each other as opposed to homes with two people who were found to be more likely to spread H1N1 between each other. Twenty eight percent of people developed flu symptoms with two people in the home, compared to nine percent in households of six people.

One in eight individuals with H1N1 symptoms in households with family members who had H1N1 flu developed respiratory symptoms. Other symptoms of swine flu include fever, general body aches, sore throat, cough, chills, fatigue, and occasionally vomiting and diarrhea. There also were no symptoms in particular that seemed to make H1N1 flu more easily transmitted; 92 percent of patients had a cough.

Looking back at H1N1 flu trends shows some differences in what we originally thought about the pandemic flu – a subject that dominated the 2009 news. The findings show that young people, less than age 18, are most susceptible to flu. Adults over age 50 are least vulnerable to getting H1N1 flu from a household member.

NEJM

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