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Commentary
CDC Comments on trH3N2 Cluster Raise Concerns
Recombinomics Commentary 21:15
September 6, 2011
Both children had potential direct or indirect exposure to pigs, Finelli said. One, a girl (sic) in Indiana, was cared for by a woman who exhibited pigs at a fair. It’s possible the caregiver had an infection she did not even notice and gave it to the child. The other case, a boy (sic) in Pennsylvania, visited a fair where there was a petting zoo and pigs on show.
The above comments by CDC “experts” raise serious concerns. The trH3N2 cluster linked to the Washington County Fair has at least three confirmed cases, the largest such cluster reported to date. The Indiana case was a boy (1M) who was taken to the Emergency Department and subsequently hospitalized. The first reported Pennsylvania case was a girl (2F) from Schulkill County who was also taken to the Emergency Department. The other two confirmed cases from Pennsylvania were still recovering on September 5, even though the fair ended two weeks ago and at least one media report indicated these two cases were hospitalized. Thus, all four of the 2011 cases appear to have sought significant medical treatment.
Moreover, all four cases involved a trH3N2 virus that acquired the M gene from pandemic H1N1. This constellation of 7 trH3N2 genes and one pandemic H1N1 gene has not been reported in any swine isolates and no earlier human cases. However, the H1N1 M gene has been called “critical” for the aerosolization of the virus and efficient transmission in humans. Thus, the presence of the H1N1 M gene, the size of the cluster in Pennsylvania, the clustering of this genetic combination in human cases, and the medical treatment for four of four cases is not “typical” for triple reassortant cases.
The current testing for trH3N2 is limited. Most cases will test as H3N2 seasonal flu, and detection of trH3N2 requires a suspicion of swine origin, which is why most testing is done on samples linked to swine or agricultural fairs. The CDC request for samples because of this cluster also asked for samples from patients with swine exposure.
Thus, the CDC is not conducting a serious epidemiological investigation of human to human transmission. As noted above, the Indiana case did not have a history of swine contact, and if the source was an asymptomatic caretaker, then after the fact investigation of the cluster in Pennsylvania would be difficult because early and mild/asymptomatic cases would have recovered and testing of relevant contacts would be difficult.
The CDC comments above raise serious concerns regarding the investigation of the Washington County Fair trH3N2 cluster, as well as serious testing for trH3N2 in patients without a swine linkage.
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