Recombinomics: Human Swine Flu Spread to Texas and Likely Import from Mexico

Commentary

Recombinomics Commentary 00:55
April 24, 2009

Now, five more cases have been seen -- all found via normal surveillance for seasonal influenza. None of the patients, whose symptoms closely resembled seasonal flu, had any direct contact with pigs.

"We believe at this point that human-to-human spread is occurring," Schuchat said. "That's unusual. We don't know yet how widely it is spreading ... We are also working with international partners to understand what is occurring in other parts of the world."

Two of the new cases were among 16-year-olds at the same school in San Antonio "and there's a father-daughter pair in California," Schuchat said. One of the boys whose cases was reported on Tuesday had flown to Dallas but the CDC has found no links to the other Texas cases.

Only one of the seven cases was sick enough to be hospitalized and all have recovered, Schuchat said.

The above comments in Reuters describe several points made in today’s CDC conference call. The additional confirmed cases leave little doubt that the swine flu is transmitting human-to-human and has now been confirmed in three distinct locations in two states (see updated map), confirming sustained transmission.

The infection of classmates in San Antonio, as well as the father and daughter in California further highlight efficient transmission. The hospitalization of one patient, who had been on a ventilator, raises concerns that infections will produce a wide range of presentations.

The location of the confirmed cases in states that border Mexico, as well as media reports of pneumonia in Canadian travelers returning from Mexico, strongly suggests that the outbreak of influenza in Mexico is also swine flu.

The confirmed cases in the United States likely represent a pandemic of H1N1 swine flu. At this point, most confirmed cases in the United States have been mild and there have been no confirmed fatalities. However, in Mexico there has been a high case fatality rate among young adults, 25-44, with atypical pneumonia, which has similarities with the 1918 pandemic.

Moreover, the 1918 pandemic was composed of eight gene segments representing recombination between H1N1 seasonal flu and H1N1 swine flu.

An efficiently transmitted swine flu can lead to co-infection with H1N1 seasonal flu. Oseltamivir resistance (H274Y) has become fixed in H1N1 seasonal flu, raising concerns that recombination or reassortment will lead to Tamiflu resistance in the swine flu, which is already resistant to amantadine and rimantadine. Moreover, the existing trivalent seasonal flu vaccine will likely offer little protection.

The spread of swine flu in the United States, and likely import from Mexico, creates a major cause for concern.

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