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Close Contact Comment Concerns
Although these cases appear to be independent events, most of those infected had close contact with pigs.
The above ProMED commentary claiming that trH3N2 has been “jumping to people from pigs” and citing “close contact with pigs” is unfortunate. The CDC puts out carefully worded and parsed reports on these cases to create an illusion of such jumps, but carefully avoids stating that the trH3N2 cases are due to swine “exposure”. The “exposure” used by the CDC can be very loose, including living in a rural area where pigs are raised, which was cited for the Pennsylvania case (A/Pennsylvanai/14/2010) in the WHO pager alert, and those with no contact or exposure are said to have “indirect” exposure when contacted by someone with exposure, such as the first trH3N2 cases in 2011, where the patients caretaker had exposure to swine.
Thus, the reports are subject to over-interpretation, as was seen in the media report which also claimed the trH3N2 was jumping from pigs to people, but the claim that most had “close contact with pigs” as stated in the ProMED commentary was well beyond the CDC reports.
The 2011 trH3N2 cases were described in a series of CDC reports for health care professionals, which detailed the swine “exposure” for the seven cases, which did not indicate most had “close contact” with swine.
The first case (2M, A/Indiana/08/2011) had no contact with or exposure to swine. His caretaker had exposure to swine in the weeks prior to symptoms in the case, but the caretaker, her family members, and associated swine were all asymptomatic.
Only one of the three Pennsylvania had close contact with swine. The “exposure” for the first case (2F A/Pennsylvania/09/2011) was attendance at an agricultural fair (Washington County fair) four days prior to symptoms. The third case (9F, A/Pennsylvania/11/2011) also attended the fair and visited a friend who exhibited swine at the fair. The only case who had close contact with swine was the second case (9F, A/Pennsylvania/10/2011) who exhibited market hogs at the fair. However, the hogs were asymptomatic, as were the other swine at the fair.
The two cases from Maine had swine exposures via visits to another agricultural fair, Fryeburg, where there were symptomatic swine. However, these swine tested negative for SOIVs. Thus, the first case’s “exposure” (8M, A/Maine/06/2011) was a fair visit. The second case (8M, A/Maine/07/2011) also participated in a pig scramble at the fair, and had exposure to swine after the fair. However, this case developed symptoms on October 22, and the fair ended on October 9, so the exposure/contact on the fair was not a source for the infection.
However, the CDC issued two November 4 reports on this case which were factually correct, but highly misleading. The report for health care professionals cited the “sick pigs” at the fair, but did not give the date of exposure. The report for the media noted that swine exposure was in the week prior to symptoms, but cited “live pigs” because the pigs were asymptomatic. Thus, the combination created the illusion that the case was exposed to sick pigs in the week prior to symptoms.
Moreover, the most recent case from Indiana (59M, A/Indiana/10/2011) was investigated by the Indiana Board of Animal Health, and none of the swine linked to the veterinarian had been symptomatic for at least 30 days prior to exposure.
Thus, the reports are carefully worded and parsed, which leads to over-interpretations as seen in the media reports which claim the exposures lead to jumps from swine to humans.. However, the ProMED report also claims “close contact” which was not stated in the CDC reports, and were not supported by the data.
Moreover, the data supporting the jump from swine to people was far from conclusive, because the pigs were asymptomatic, and prior to yesterday, this novel trH3N2 had not been identified in swine. The sequences released yesterday were for a September 13 New York isolate, A/swine/NY/A01104005/2011, which was after the widespread detection in human cases in July and August in Indiana and Pennsylvania, and may signal jumps from humans to swine. The USDA sequenced all eight gene segments and all were the same lineage as the seven human cases and were easily identified as the same sub-clade. In addition, the detection also highlighted the failure to detect this novel sub-clade in swine prior to the human cases, in spite of increased swine surveillance.
The swine surveillance contrasted with the human surveillance, which has been abysmal. Maine has only identified two influenza cases this season, and both were trH3N2. Indiana has only identified three flu cases since late July, and two of the three were trH3N2. Pennsylvania has not issued a weekly report for the 2011/2012 season, but the CDC has sequenced two H3N2 cases since the sequencing of the three cases who attended the fair. Both were adults, so all three of the adolescent cases in Pennsylvania since July have been trH3N2.
This minimal surveillance in cases without swine exposure has been fueled by the CDC request for samples from patients with swine exposure, Maine CDC advisory which claimed that all prior 2011 trH3N2 cases had swine exposure, and reports claiming jumps from swine to humans, as noted for the media and ProMED reports.