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Paradigm Shift Intervention Monitoring
200 H3N2v Cases
In Gallia County Ohio
There have been 200 suspected cases reported; 69 of those tested positive for Influenza A using the rapid flu test. Representative samples of the suspected cases have been sent for further testing.
There are currently 4 confirmed cases of H3N2v in Gallia County. All individuals had direct contact with swine at fairs.
The above comments from the Gallia County Health Department in Ohio provide insight on the relationship between the number of H3N2v cases and the number of confirmed cases. Earlier reports cited 62 cases confirmed by the influenza A rapid test, which suggested more than 150 cases were tested.
The above update increases the number of influenza A confirmed cases to 69, but as noted in the August 9 CDC telebriefing, seasonal influenza levels in the United States are low, so most state lab confirmed cases with be H3N2v, especially when linked to an outbreak at an agricultural fair.
Thus, it is likely that the 200 symptomatic cases were H3N2v infected, although CDC confirmation is lagging and only four confirmed cases from Gallia County have been reported and included in the CDC update. However, the CDC has ceded H3N2v confirmation to the state labs, so the number of “confirmed” cases is expected to increase significantly in today’s MMWR as well as future updates by state labs as well as the upcoming Friday updates by the CDC.
However, as seen in the above outbreak associated with the Gallia Junior County fair, many infected cases will not be tested, and the number of “confirmed” cases will significantly undercount large outbreaks.
However, the CDC has targeted testing of ILI cases associated with agricultural fairs, which limits detection of human to human transmission in clusters with too many to test. These largely outbreaks clearly demonstrate the ability of the current H3N2v to infect large numbers of humans.
The recently released sequences from confirmed cases in Hawaii, Indiana, and Ohio represent a novel sub-clade which was first reported at the West Virginia day care center in Mineral County in late 2011. This sub-clade (A/West Virginia/06/2011 and A/West Virginia/07/2011) had an NA gene that was distinct from the NA in the first human H3N2v cases in 2011, which has not been acknowledged by the CDC. The matching of this sub-clade with all 2012 human H3N2v sequences (from Utah, Hawaii, Indiana, and Ohio) signals human adaptation, as well as human to human spread as seen at the day care center were there was no swine exposure, but 23 of the 70 contacts of the index case had ILI, and H3N2v was confirmed in one of the classmates.
The recently flu outbreak at a summer camp in Glen Spey, New York, suggests this H3N2v sub-clade continues to spread in cases with no swine exposure.
However, such recent cases and clusters have not been reported by the CDC.