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Cumberland Pig Scramble Raises trH3N2 Swine Exposure Issues
Recombinomics Commentary 01:25
November 15, 2011

One case of human infection with a novel influenza A virus was reported by the Maine Center for Disease Control and Prevention. The patient was infected with a swine origin influenza A (H3N2) virus. Testing performed at Maine’s Health and Environmental Testing Laboratory on October 14, 2011 indicated a likely swine origin influenza A (H3N2) virus and this result was confirmed at CDC on October 16, 2011. The patient reported attendance at an event where pigs were present in the week preceding symptom onset on October 7, 2011, did not require hospitalization, and continues to recover.

Two human infections with novel influenza A viruses were detected in individuals from two states (Indiana and Maine). Both patients were infected with swine-origin influenza A (H3N2) viruses. One patient was hospitalized, but has now been discharged and both continue to recover from their illnesses. Both patients reported close contacts with pigs preceding their illness onset.

The above comments from CDC FluView for weeks 41 and 43 describe the two trH3N2 cases from Maine.  The first case, A/Maine/06/2011,  was detailed with regard to exposure and onset date, and the characterization sheet linked above indicated the sequence came from an Oct 10, 2011 collection from an 8M.  The description for the second case was vague, but the characterization sheet from the sequence, A/Maine/07/2011, indicated the sample was collected two weeks after the first case, Oct 24, and the CDC report at the WHO Event Information Site for IHR National Focal Point assigned the event to Oct 22.

Recombinomics' discussions with personnel at the Maine CDC as well as the Maine Agriculture Department indicated both cases were exposed to swine at an agricultural fair and one case participated in a pig scramble.  The first patient was from Cumberland County and the agricultural fair that matches the descriptions was the Cumberland County Fair that was open from September 25 to October 1 and included a pig scramble at 9 AM on October 1, which was open to Cumberland County residents.  A public video of the boy pig scramble is available at youtube.  Testing of swine at the fair is still ongoing, but initial results were negative for SOIV.  Some swine at the event were said to be symptomatic, but the swine in the video appear to be healthy.

These two cases demonstrate the power of suggestion and the extreme testing bias by the CDC.  Since the fair ended on Oct 1, there is little chance that the swine at the fair were the source of the trH3N2 in second case, and the identity between the sequences from both isolates reduces the likelihood that the swine at the fair were the source of infection of the first case.  Similarly, the 6 day gap between the end of the fair and disease onset also reduces the likelihood of a link between swine at the fair and the first case.

The identical constellation of flu genes in all seven 2011 trH3N2 cases signal human transmission, but mild cases at this time of year are unlikely to be tested for trH3N2 unless there is a swine ”exposure”, such as those described for the two cases in Maine.  To date there have been no reports of swine infected by  the novel trH3N2, identified in all seven human cases, and human swine exposure links are driven by heavily biased testing.  Cases with a swine exposure are aggressively tested, while those without a swine link are not sub-typed (and sub-typing is required for trH3N2 testing), as seen in the week 44 FluView or 31/32 influenza A positive cases in Region 4.

An aggressive testing campaign of symptomatic patients, with a focus on adolescents without swine contact, is long overdue.

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