Studies: Swine flu spreads long after fever stops (Update)

Sep 14, 2009 By MARILYNN MARCHIONE , AP Medical Writer
Graphic shows a timeline of how doctors believe the swine flu progresses during its contagious phase

(AP) -- When the coughing stops is probably a better sign of when a swine flu patient is no longer contagious, experts said after seeing new research that suggests the virus can still spread many days after a fever goes away.

The federal Centers for Disease Control and Prevention has been telling people to stay home from work and school and avoid contact with others until a day after their fever breaks. The new research suggests they may need to be careful for longer - especially at home where the risk of spreading the germ is highest.

Swine flu also appears to be contagious longer than ordinary seasonal flu, several experts said.

"This study shows you're not contagious for a day or two. You're probably contagious for about a week," said Gaston De Serres, a scientist at the Institute of Public Health in Quebec.

He presented one of the studies Monday at an American Society for Microbiology conference. It is the first big meeting of infectious disease experts since last spring's emergence of swine flu, which now accounts for nearly all of the flu cases in the United States. More than 1 million Americans have been infected and nearly 600 have died from it, the CDC estimates.

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."

Doctors know that people can spread ordinary seasonal flu for a couple of days before and after symptoms start by studying virus that patients shed in mucus. The first such studies of swine flu are just coming out now, and they imply a longer contagious period for the novel bug.

"It's probably realistic that this virus sheds much longer than seasonal flu," said Dr. Jonathan McCullers, an infectious diseases specialist at St. Jude Children's Research Hospital in Memphis, Tenn.

Three reports suggest this is so. De Serres and other researchers in Canada took nose and throat swabs from 43 patients with lab-confirmed flu and dozens of other sick family members.

On the eighth day after symptoms first appeared, 19 to 75 percent showed signs of virus remaining in their noses, depending on the type of test used.

"This proportion appears to be very big, and it is," but it's not clear how much virus is needed to actually spread flu, so the lower number is more reliable, he said.

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 five days after symptoms began, and 40 percent seven days after. Some still harbored 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 third report came from Dr. Guillermo Ruiz-Palacios of the National Institutes of Medical Science and Nutrition in Mexico, where the first 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. This was especially true of obese people, and patients who started on medicines longer than two days after symptoms first appeared.

The new reports suggest a longer contagious period for swine flu, but how long is not clear, Cox said. Even with it in your nose, "you might not be shedding enough virus to infect other people," she said.

That is why signs like coughing may matter more, De Serres said.

"Contagiousness varies, not only with the presence of the virus, but the other symptoms that would make you transmit," he said.

Swine flu symptoms can include fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills and fatigue, and sometimes diarrhea and vomiting. Young children may be cranky, less playful or not eat as much as normal, the CDC advises.

The agency's advice to stay home for a day after fever breaks does not apply to health care settings. There, confinement for seven days from the start of symptoms - or until they go away, whichever is longer - is still advised.

People who have had swine flu should cover their mouths when they cough or sneeze and wash their hands a lot once they do return to work and school, the CDC says.

---

On the Net:

Swine flu info: http://www.flu.gov

CDC advice: http://www.cdc.gov/h1n1flu/guidance/exclusion.htm and http://www.cdc.gov/h1n1flu/qa.htm

Medical conference: http://www.icaac.org

©2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Explore further: Genomes of malaria-carrying mosquitoes sequenced

add to favorites email to friend print save as pdf

Related Stories

Swine flu cases up to 7, probe expanding

Apr 23, 2009

(AP) -- Health officials say a unique type of swine flu has now been diagnosed in seven people in California and Texas, up from the two reported earlier this week. The five new cases in the two states have all recovered, ...

US says Tamiflu for the sick, not a preventive

Sep 08, 2009

(AP) -- Federal health officials put out new guidelines Tuesday that say the flu medicines Tamiflu and Relenza should only be used to treat people who are sick with the flu and at high risk for complications.

Can a mop fight swine flu? Docs say probably not

May 20, 2009

(AP) -- In scores of schools across the United States, the mop has been the weapon of choice in the fight against swine flu. Schools from New York to California have spent days disinfecting desks and tables after cases of ...

Mexico City closes museums to stop flu outbreak

Apr 24, 2009

(AP) -- Mexico's federal government has closed museums, libraries, and state-run theaters as well as schools in its overcrowded capital to stop a swine flu outbreak authorities say may have killed as many ...

Britain's swine flu advice confuses public

Jul 20, 2009

(AP) -- As swine flu continues to spread in Britain, health officials are telling people to avoid travel and crowded places, and even advising women to delay getting pregnant until the virus subsides.

Recommended for you

Genomes of malaria-carrying mosquitoes sequenced

16 hours ago

Nora Besansky, O'Hara Professor of Biological Sciences at the University of Notre Dame and a member of the University's Eck Institute for Global Health, has led an international team of scientists in sequencing ...

How calcium regulates mitochondrial carrier proteins

Nov 26, 2014

Mitochondrial carriers are a family of proteins that play the key role of transporting a chemically diverse range of molecules across the inner mitochondrial membrane. Mitochondrial aspartate/glutamate carriers are part of ...

Team conducts unprecedented analysis of microbial ecosystem

Nov 26, 2014

An international team of scientists from the Translational Genomics Research Institute (TGen) and The Luxembourg Centre for Systems Biomedicine (LCSB) have completed a first-of-its-kind microbial analysis of a biological ...

Students create microbe to weaken superbug

Nov 25, 2014

A team of undergraduate students from the University of Waterloo have designed a synthetic organism that may one day help doctors treat MRSA, an antibiotic-resistant superbug.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.