Swine Flu Q&A: Can I infect my family if I don't have symptoms?

I'm teacher in a Bronx junior high that has had high absences because of swine flu. A fellow teacher in my school, who has asthma, was hospitalized for a week with the flu. I have no symptoms, but I'm afraid I could carry the germ to my young granddaughter or elderly parents. Is it possible to carry the flu without having symptoms? I'm avoiding seeing my family for fear of getting them sick. Am I overreacting? —D. S., Bronx, N.Y.

We can't tell you if you're overreacting—everyone's risk tolerance is their own. But we can try to put your risk of infecting your relatives in perspective.

Yes, it is possible to transmit the flu without experiencing symptoms. If you've contracted the virus, for the first few days of infection you may be contagious without showing symptoms of the flu. It is also possible to be infected without ever showing symptoms at all. The Centers for Disease Control and Prevention estimates that the incubation period (between contracting the virus and showing symptoms) is likely is about 1 to 4 days, but may be as long as 7 days.

The attack rate for the swine (H1N1) flu, or the percentage of people exposed who are likely to become infected, is similar to seasonal flu, according to the CDC. That means that once the virus is present in the community it may spread to approximately 7 to 10 percent of the population.

Within households where the virus is present, the attack rate is likely to be higher, around 20 percent of people.  Overall however, the likelihood of spreading the disease if you don't have symptoms is somewhat lower, because the symptoms themselves help to spread the virus.  Flu viruses are primarily transmitted through respiratory droplets propelled through the air by coughing and sneezing.

If you believe you've been exposed to the virus, but don't have symptoms, you can lower the risk of infecting others by taking some of the same preventative measures that you might use if you had symptoms, such as limiting physical contact—including kissing and hugging—and generally staying about three to six feet away from others; washing hands with soap and water frequently and for at least 20 seconds; and covering coughs and sneezes with a tissue or your elbow or shoulder.

Quarantining yourself from loved ones goes beyond current health recommendations for those without symptoms. But each of us has to decide what risks we are willing to take for ourselves and our families. Good hygiene and limiting physical contact can reduce the chance of spreading the virus—but they do not reduce the chance of infection to zero.

—Kevin McCarthy, associate editor

Image: Centers for Disease Control and Prevention