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INFLUENZA PANDEMIC (H1N1) 2009 (48): CONTAGIOUS PERIOD
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A ProMED-mail post
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International Society for Infectious Diseases
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Date: Mon 14 Sep 2009
Soure: healthzone.ca, Associated Press report [edited]
<http://www.healthzone.ca/health/newsfeatures/article/695679>
Swine flu contagious longer than thought
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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 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. 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 2. 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 [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.
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 1st 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, Tennessee.
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 8th day after
symptoms 1st 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 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. This was especially true of obese
people, and patients who started on medicines longer than 2 days after
symptoms 1st 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 7 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.
[Byline: Marilynn Marchione]
--
Communicated by:
ProMED-mail Rapporteur Mary Marshall
[Despite these findings it seems unlikely that the CDC will amend its
advice on how long people with influenza pandemic (H1N1) 2009 virus
infection should remain in isolation. It is probable that Nancy Cox's
view will prevail that long periods of isolation no longer seem
appropriate, especially as the virus seems to cause mostly mild
illness. Influenza pandemic (H1N1) 2009 virus is spreading so widely
now that: "It's just virtually impossible not to have virus introduced
into settings such as schools and universities." The data reported
above suggest a longer period of retention of influenza pandemic
(H1N1) 2009 virus in the nose, but even so there may not be sufficient
infectivity retained to transmit infection. - Mod.CP]
[see also:
Influenza pandemic (H1N1) 2009 (47): Spain, ICU patients 20090914.3234
Influenza pandemic (H1N1) 2009 (46): WHO update 65 20090911.3209
Influenza pandemic (H1N1) 2009 (45): antiviral resistance 20090911.3207
Influenza pandemic (H1N1) 2009 (44): receptor binding 20090910.3192
Influenza pandemic (H1N1) 2009 (43): pediatric questions 20090909.3185
Influenza pandemic (H1N1) 2009 (42): China, pork consumption 20090907.3146
Influenza pandemic (H1N1) 2009 (41): Iran 20090906.3140
Influenza pandemic (H1N1) 2009 (40): global update 20090906.3138
Influenza pandemic (H1N1) 2009 (39): pediatric deaths 20090904.3118
Influenza pandemic (H1N1) 2009 (38): 10 S.Amer. presidents exposed
20090831.3063
Influenza pandemic (H1N1) 2009 (37): 2nd wave plan, WHO 20090830.3042
Influenza pandemic (H1N1) 2009 (36): USA (IL), NZ 20090828.3032
Influenza pandemic (H1N1) 2009 (35): NZ surveillance 20090827.3022
Lnfluenza pandemic (H1N1) 2009 (34): Tamiflu shelf-life 20090826.3006
Influenza pandemic (H1N1) 2009 (33): cases, fatalities 20090820.2955
Influenza pandemic (H1N1) 2009 (32): Tamiflu use policy 20090817.2914
Influenza pandemic (H1N1) 2009 (31): drug resistance 20090815.2900
Influenza pandemic (H1N1) 2009 (30): assumptions 20090813.2879
Influenza pandemic (H1N1) 2009 (20): Peru, 33 percent asymptomatic
20090730.2668
Influenza pandemic (H1N1) 2009 (10): vaccine 20090720.2577
Influenza pandemic (H1N1) 2009 - Viet Nam: patient data 20090708.2450]
....................cp/ejp/jw
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