Labs confirm same swine flu in deadly Mexican outbreaks

Apr 24, 2009 (CIDRAP News) – Samples from a deadly respiratory illness outbreak in Mexico match swine influenza isolates from patients in the United States who had milder illnesses, an official from the US Centers for Disease Control and Prevention (CDC) said today, fueling speculation that the World Health Organization (WHO) could be on the verge of raising the global pandemic alert level.

Richard Besser, MD, the CDC's acting director, told reporters today during a press teleconference that the development is worrisome. "Our concern has grown since yesterday, based on what we've learned," he said. "We do not know if this will lead to the next pandemic, but our scientists are monitoring it and take the threat very seriously."

The swine flu A/H1N1 strain has been confirmed in one more US citizen, a child from San Diego who has recovered, raising the total number of US cases to eight, Besser said. The virus contains gene segments from four different influenza types: North American swine, North American avian, human, and Eurasian swine.

The WHO said today that Mexican officials have reported three separate events. In the Federal District, the number of cases rose steadily through April, and as of yesterday, more than 854 cases of pneumonia, 59 of them fatal, had been reported in Mexico City.

The illness outbreak in Mexico City prompted the country's health minister, Jose Cordova, to cancel classes in Mexico City today and advise students and adults to avoid crowded public places and large events, Bloomberg News reported.

Mexican officials also reported 24 cases with 3 deaths from an influenza-like illness in San Luis Potosi, in the central part of the country, and 4 cases with no deaths in Mexicali, near the US border, the WHO reported.

The virus in Mexico has primarily struck otherwise healthy young adults, the WHO said, which is a departure from seasonal influenza, which typically affects the very young and very old.

The CDC's laboratory analyzed 14 samples from severely ill Mexican patients and found that 7 of them had the same swine flu mix as the virus that infected the US patients. However, Besser called the analysis preliminary and said the CDC doesn't yet have enough information to draw conclusions. "We still don't have enough information about the extent of the spread or the illness spectrum."

The WHO said today Canada's national laboratory has confirmed swine flu A/H1N1 in 18 isolates from Mexican patients, of which 12 were genetically identical to the swine flu viruses from California.

The WHO and CDC both said they were sending representatives to Mexico to assist local authorities, and the WHO said it has alerted its Global Alert and Response Network.

Besser said the WHO will likely convene an expert panel to discuss raising the pandemic alert level from 3 (human infection with new influenza subtype with only rare human-to-human spread) to 4 (small clusters with localized human-to-human transmission). He said the experts will consider three factors: the novelty of the virus, disease severity, and how easily transmission of the virus is sustained.

Global health officials might consider a containment strategy such as dispatching antiviral medications to affected parts of Mexico in an attempt to stop the spread of the virus, but Besser said that such a measure might not work, because there are signs that the virus has already spread from human to human over long distances. "A focused, well defined area is not something we've seen here," he said.

CDC officials have said the swine flu A/H1N1 virus is susceptible to the newer antivirals oseltamivir (Tamiflu) and zanamivir (Relenza), but not the older ones, amantadine and rimantadine.

Jeff McLaughlin, a spokesman for GlaxoSmithKline, the maker of Relenza, told CIDRAP News that the company is watching the swine flu developments closely. Terry Hurley, a spokesman for Roche, which produces Tamiflu, said its "rapid response stockpile" is on 24-hour standby, as usual, for deployment to the WHO, which has not yet requested it.

The threat from the swine flu virus serves as a reminder for individuals and businesses to think about their own level of preparedness, Besser said. "This is a time for people to be thinking about that teachable moment."

So far, federal officials have not changed their travel recommendations to California, Texas, or Mexico, though they have issued an advisory about the increased health risk in certain parts of Mexico, urging travelers to take standard precautions such hand washing, staying home when sick, and using good coughing and sneezing hygiene. 

See also:

Apr 24 WHO report

Apr 23 CIDRAP News story "More US swine flu cases, Mexico illnesses raise pandemic questions"

Apr 22 CIDRAP News story "Swine flu cases recall 1976 episode"

Apr 21 CIDRAP News story "Human swine flu cases with unique strain raise concern"

CDC swine flu investigation page

CDC swine flu information

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