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Commentary
Spike In H1N1 In Texas
and Alabama Raises Concerns
Recombinomics
Commentary 13:01
March 14, 2010
There were two culture-confirmed cases of Type A influenza in December, three in January and seven in February — all found to be of the swine flu subtype, Demmler-Harrison said.
Five cases of Type A influenza surfaced in the first week of March, but tests are still pending to determine if those are swine flu, she said.
At Andalusia Regional Hospital, positive flu cases are averaging about one per day, said Candie Northey ARH’s director of infection.
“We can’t confirm whether these are H1N1 or typical seasonal flu because the tests we utilize are simple ‘quick tests’ and only reveal positive or negative flu,” Northey said. “We have noted five positive tests through our lab in the last five days, and while this is not a lot, I do feel the need to refresh everyone on how to prevent the spread of flu.”
The same can be said at Opp’s Mizell Memorial Hospital, where Marsha Seppala, MMH’s director of case management and infection prevention, said the first of the year started out relatively slow for positive flu cases.
The above comments describe increases in Type A influenza cases in early March in the Houston area, as well as two cities in southern Alabama. In the US, seasonal type A flu cases have virtually disappeared. In 2010 there has only been one confirmed seasonal H1N1 in the entire country, and there has also only been one H3N2 case in the past five weeks. Therefore, the increase in type A described above is an increase in pandemic H1N1.
This increase is not unexpected. Although reporters have been requesting a declaration that the 2009/2010 pandemic has ended, each of the past three pandemics had a fall and spring wave. Moreover, the seasonal flu was crowded out, as has happened with seasonal H1N1 and H3N2. Therefore, there is no evidence against a spring wave.
In the US the first confirmed swine flu cases were on samples collected March 30 and April1, 2009. However, the confirmed cases were from clusters involving earlier infections, which would have involved swine H1N1 infections that began almost exactly one year ago. That outbreak peaked in May, and a similar time frame is expected for 2010.
Pandemic waves begin when a high percentage of the target population has little or no immunity and end when the population does have immunity. A new wave is driven by a virus that has evolve away from the immunity, as indicated by “low reactor” status, such as those with G158E. This polymorphism began to expand in the US during the fall wave, and then began to appear in larger numbers in Japan in December.
However, the appearance of G158E in the most recent public sequences, two Feb 26 isolates from swine in Minnesota is cause for concerns. These two isolates represent the same sub-clade found in Ukraine, Russia and Norway that had D225G and were linked to fatal cases. However, the virus is circulating in swine and isolates in Illinois and Minnesota have picked up the same swine polymorphisms. The detection of the same H1N1 in Minnesota and Illinois indicates the virus is circulating in swine, and the two most recent isolates from Minnesota have added G158E. Since these isolates are the pandemic H1N1 sub-clade that is widespread in Ukraine, it can jump back into the human population and introduce the swine acquisitions. Both G158E and D225G are common in swine. Moreover, 1918 sequence have an equal mixture of human and swine H1N1polymorphisms acquired via recombination, which would also produce new acquisitions in the Minnesota swine, including G158E.
Thus, the above reports signal the start of a spring wave, and the increases in low reactor polymorphisms like G158E and D225G are likely candidates for increases due to positive selection pressure, which would lead to more severe and fatal cases.
Sequence data on the emerging cass in March would be useful.
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