Another H3N2v Confirmation In Minnesota
August 29, 2012
“We expect to continue seeing new cases of this illness, at least for a while,” said Deputy State Epidemiologist Richard Danila, “However, we have not seen any change in the behavior of this virus. We have been actively looking for cases. We are recommending that clinicians ask patients about swine contact, and send clinical samples for patients with influenza symptoms.”
The above comments from the Minnesota Department of Health press release on their third reported H3N2v case, highlights the biased sampling of H3N2v positive cases. The press release does not mention testing of off season ILI cases, which typically are not tested or forwarded to state labs. Instead physicians have been asked to send samples from ILI cases with swine contact, to maintain the testing bias.
The CDC has released the sequences from the first Minnesota case, A/Minnesota/11/2012, which has NA N234D in an NA sequences that is identical to 8 cases from Butler County, Ohio and 4 cases from LaPorte, Indiana. All 34 sets of H3N2v sequences from July and August collections are closely related and represent the clonal expansion of a sub-clade closely related to sequences from a West Virginia day care center with no swine exposure.
The H3N2v is clearly transmitting human to human, which is why all 34 sequences are closely related but are from 7 states (Hawaii, Indiana, Ohio, Maryland, Minnesota, Pennsylvania, and Wisconsin). Testing is largely limited to samples from ILI cases with swine exposure, leading to a pseudo-linkage, which is used to collect more samples to expand the linkage.
The recent H3N2v outbreak in Gallia County, Ohio involved hundreds of cases. 200 of the symptomatic cases were tested with a rapid test, and the 69 influenza A positives indicated virtually all of the 200 tested were infected by influenza A, which was confirmed by the initial testing by the Ohio Department of Health which initially cited 11 confirmed cases and recently added a 12th case. The West Virginia Department of Health also reported 3 confirmed cases in Mason County who attended the Gallia Junior County fair which was held five miles from the Mason County border.