September 2009

Pandemic Influenza Alert

Hung Cheung, MD, MPH, FACOEM                         

Sherry Sood, MD, MPH                                                

Dr. Cheung/ OEM Advisor, LLC.

An environmental colleague from Midlothian, Virginia posed a great question concerning the period of H1N1 infectivity and given the new scientific findings on this, the staff felt that it should be addressed prior to next month's update. Please feel free to call or email us with any questions or forward the attachment to those who may have questions about H1N1. We will monitor the situation and will have periodic updates for you. They will also be posted on our web site under the “In the News” tab.  We hope this helps as we strive to be your environmental, occupational and public health resource. 

How long are those ill from H1N1 contagious?

The Centers for Disease Control and Prevention (CDC) has been telling people to stay home from work and school and avoid contact with others until a day after their fever breaks. New research data suggest they may need to be careful for longer. Swine flu also appears to be contagious longer than ordinary seasonal flu, several experts said. Presenting at an American Society for Microbiology conference Gaston De Serres, a scientist at the Institute of Public Health in Quebec noted "This study shows you're not contagious for a day or 2. You're probably contagious for about a week." He presented one of the studies Monday [14 Sep 2009] at an American Society for Microbiology conference. It is the 1st big meeting of infectious disease experts since last spring's emergence of swine flu [influenza pandemic (H1N1) 2009 virus], which now accounts for nearly all of the flu cases in the United States. More than one million Americans have been infected and nearly 600 have died from it, the CDC estimates.

Dr. David C. Lye reported on 70 patients treated at Tan Tock Seng Hospital in Singapore. Using a very sensitive test to detect virus in the nose or throat, he found that 80 percent had it 5 days after symptoms began, and 40 percent 7 days after. Some still harboured virus as long as 16 days later. How soon they started on antiviral medicines such as Tamiflu made a difference in how much virus was found, but not whether virus was present at all.

A 3rd report came from Dr. Guillermo Ruiz-Palacios of the National Institutes of Medical Science and Nutrition in Mexico, where the 1st cases of swine flu were detected. Infected people "shed the virus for a very, very long time," often for more than a week after the start of symptoms, he told the conference.

It is unclear whether the new research will lead the CDC to rethink its advice on how long people with swine flu should hole up. Long breaks from school and work do not seem worth it for a virus that now seems to cause mostly mild illness, said the CDC's flu chief, Nancy Cox. Swine flu is spreading so widely now that confining the sick does less good, she said. "We tried to have our guidance balance out all of these factors," she said. "It's just virtually impossible not to have virus introduced into settings such as schools and universities."