Mexican flu outbreak may be mild -U.S. CDC
* Tests show the virus has not mutated
* Pattern of disease resembles seasonal influenza
* Easy spread suggests many mild cases never detected (Updates throughout with quotes from news conference, details)
By Maggie Fox, Health and Science Editor
WASHINGTON, May 1 (Reuters) - The outbreak of a new and worrying kind of influenza in Mexico may not be as severe as it first looked, with many mild cases that were not immediately noticed, U.S. health experts reported on Friday.
What has been seen of the virus as it spreads globally suggests it is acting more like a regular seasonal flu than anything more frightening, officials at the U.S. Centers for Disease Control and Prevention said.
Health workers are rushing to get a fuller picture of the outbreak of H1N1 swine flu, which the World Health Organization fears could tip into a pandemic.
Mexico, the worst-hit country, has reported up to 176 deaths from the new strain. Cases have been reported around the world, mostly among travelers from Mexico, but they have been mild and most people recovered so far with little or no treatment.
The only death outside Mexico was a Mexican toddler visiting Texas. None of the five children in Mexico with confirmed H1N1 infection died.
Experts have been struggling to explain why there have been so many deaths in Mexico and not elsewhere, but the CDC report suggests a simple explanation -- there are many cases in Mexico, most are mild, and just the bad ones have been seen so far.
"The clinical spectrum of swine-origin influenza A (H1N1) virus illness is not yet well characterized in Mexico. However, evidence suggests that swine-origin influenza A (H1N1) virus transmission is widespread and that less severe (uncomplicated) illness is common," the CDC, Mexico's Health Ministry and other health agencies said in a special report.
The same is true in the United States, the country with the most confirmed cases -- 141 -- after Mexico.
Most have been mild, with just five people sick enough to go to the hospital.
EASILY SPREADS
The CDC's Dr. Anne Schuchat said the new strain is about as infectious as seasonal flu, with an "attack rate" -- the rate of infection in a population -- of 25 percent to 30 percent.
"It is easily spread from person to person," Schuchat told a news conference."
Genetic analysis from several countries shows the virus has not mutated, so the people in Mexico are not being sickened by a virus that is somehow more virulent, the CDC added.
"In Mexico, their first attention was to more severe illness and we learned about those cases earlier. As they looked more, they found more," Schuchat said.
The report says: "Therefore, a large number of undetected cases of illness might exist in persons seeking care in primary-care settings or not seeking care at all."
Critics have begun asking whether the CDC and WHO may have overreacted to the outbreak but Schuchat stressed that scientists are just beginning to build a picture of the situation.
"Public health is trying to strike a balance," she said. "We are trying to have interventions that will not be more harmful than the virus itself."
The CDC has sent test kits to Mexico that will help get a better picture of who is sick. It is difficult to know without special tests because respiratory diseases are so common and many infection look like flu.
Even garden-variety flu can be deadly. Seasonal influenza kills an estimated 250,000 to 500,000 people globally every year. (Editing by Mohammad Zargham)
* Pattern of disease resembles seasonal influenza
* Easy spread suggests many mild cases never detected (Updates throughout with quotes from news conference, details)
By Maggie Fox, Health and Science Editor
WASHINGTON, May 1 (Reuters) - The outbreak of a new and worrying kind of influenza in Mexico may not be as severe as it first looked, with many mild cases that were not immediately noticed, U.S. health experts reported on Friday.
What has been seen of the virus as it spreads globally suggests it is acting more like a regular seasonal flu than anything more frightening, officials at the U.S. Centers for Disease Control and Prevention said.
Health workers are rushing to get a fuller picture of the outbreak of H1N1 swine flu, which the World Health Organization fears could tip into a pandemic.
Mexico, the worst-hit country, has reported up to 176 deaths from the new strain. Cases have been reported around the world, mostly among travelers from Mexico, but they have been mild and most people recovered so far with little or no treatment.
The only death outside Mexico was a Mexican toddler visiting Texas. None of the five children in Mexico with confirmed H1N1 infection died.
Experts have been struggling to explain why there have been so many deaths in Mexico and not elsewhere, but the CDC report suggests a simple explanation -- there are many cases in Mexico, most are mild, and just the bad ones have been seen so far.
"The clinical spectrum of swine-origin influenza A (H1N1) virus illness is not yet well characterized in Mexico. However, evidence suggests that swine-origin influenza A (H1N1) virus transmission is widespread and that less severe (uncomplicated) illness is common," the CDC, Mexico's Health Ministry and other health agencies said in a special report.
The same is true in the United States, the country with the most confirmed cases -- 141 -- after Mexico.
Most have been mild, with just five people sick enough to go to the hospital.
EASILY SPREADS
The CDC's Dr. Anne Schuchat said the new strain is about as infectious as seasonal flu, with an "attack rate" -- the rate of infection in a population -- of 25 percent to 30 percent.
"It is easily spread from person to person," Schuchat told a news conference."
Genetic analysis from several countries shows the virus has not mutated, so the people in Mexico are not being sickened by a virus that is somehow more virulent, the CDC added.
"In Mexico, their first attention was to more severe illness and we learned about those cases earlier. As they looked more, they found more," Schuchat said.
The report says: "Therefore, a large number of undetected cases of illness might exist in persons seeking care in primary-care settings or not seeking care at all."
Critics have begun asking whether the CDC and WHO may have overreacted to the outbreak but Schuchat stressed that scientists are just beginning to build a picture of the situation.
"Public health is trying to strike a balance," she said. "We are trying to have interventions that will not be more harmful than the virus itself."
The CDC has sent test kits to Mexico that will help get a better picture of who is sick. It is difficult to know without special tests because respiratory diseases are so common and many infection look like flu.
Even garden-variety flu can be deadly. Seasonal influenza kills an estimated 250,000 to 500,000 people globally every year. (Editing by Mohammad Zargham)
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