Novel influenza A (H1N1) is contagious longer than originally thought

Marilynn Marchione of the Associated Press reported last night on a series of studies which find the pandemic influenza A (H1N1) virus has a longer infectious period (meaning people may be contagious longer) than originally thought, longer than seasonal influenza viruses.

One study conducted by the Institute of Public Health in Quebec, Canada found that among 43 patients with lab confirmed novel H1N1 infections and dozens of family members who submitted nose and throat swabs, 19-75% still harbored the virus in their noses 8 days after symptom onset (the time when their first symptoms began). Similarly, Dr. Guillermo Ruiz-Palacios of the National Institutes of Medical Science and Nutrition reported that infected people shed the virus for more than a week after they became symptomatic. A study out of Tan Tock Seng Hospital in Singapore illustrated that 80% of 70 study patients harbored the virus 5 days after symptom onset, 40% harbored the virus 7 days after symptom onset, and some harbored the virus as long as 16 days after symptom onset. Factors such as length of time from symptom onset to initiation of treatment with Tamiflu and underlying medical conditions, including obesity, may influence the length of time a person harbors the virus.

While this new information may have implications for public health recommendations, there is still some uncertainty about how long the infectious period may last because even though people harbor the virus in their noses, they still may not shed enough virus to infect others. An important take home message from the results of these studies - wash your hands and practice good hygiene (cover your coughs/sneezes).

The entire Associated Press article can be viewed at: http://www.thestar.com/news/world/article/695679