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Commentary
H3N2
Swine Pandemic Surveillance Concerns
Recombinomics
Commentary 18:20
December 18, 2010
The patient became ill with a swine origin influenza A (H3N2) virus infection in November.
The patient required hospitalization, but has since recovered.
The above comments describe the most recent reported trH3N2 case in the United States and highlight the reporting delays, which were also seen in the Wisconsin case. The pager alert describe a 7 month old child with a disease onset date of September 6, but the characterization sheet for the sequence has the sample date as November 2 and the pager alert was November 10, which was then followed by a notification in FluView, followed by a notice in MMWR.
Even longer delays were seen in the Iowa case, who was infected in September, 2009, investigated in November, 2009, and reported in January, 2010.
These long delays are almost certainly due to detection by routine surveillance. Unlike the triple reassortant that caused the 2009 pandemic, trH3N2 viruses have a human HA and NA. Therefore, these samples generate H3N2 results when sero-typed with reagents directed against human sequences, and the triple reassortant nature of the virus is only determined by later testing such as antigenic characterization and/or sequencing.
These long delays severely impact epidemiological analysis because there would not be appropriate samples collected from contacts, who would have been infected weeks or months earlier.
Thus, at this time it is not clear if there have been additional trH3N2 cases in November or December, and lab confirmation of human to human transmission is also unlikely.
The timing of the three most recent cases (September, October, and November), as well two cases in Minnesota this year, raises concerns that there is human trH3N2 transmission. This concern is increased by sequence analysis of the first five examples. Four of the five are closely related to each other, and more closely related to each other than swine trH3N2 sequences, even though collections are over a year apart and cover four different states (Kansas, Minnesota, Wisconsin, Pennsylvania) and there have been many recent trH3N2 sequences from the same states.
Moreover, contact with swine is frequently reported, but there are no reports of trH3N2 isolations from the contact swine.
Thus, the sequences, timing, and locations associated with these trH3N2 cases support human to human transmission, dictating more aggressive and timely surveillance for trH3N2 in these areas.
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