H3N2v Coles County Cases Increase In Illinois
August 18, 2012
A second case of flu transmitted by contact with swine was confirmed by Coles County health officials
Cathie Reynolds, nursing director of the Coles County Health Department, said tests now show that two children who attended the Coles County Fair and visited its livestock barns contracted the H3N2v flu virus. She said tests results are pending on two other children who also visited the fair’s livestock areas and showed flu symptoms.
In addition to the two confirmed cases, tests showed that two children and one adult did not contract the H3N2v virus, Reynolds said.
The above comments indicate the number of H3N2v cases linked to the Coles County Fair in Illinois was significantly higher than the two confirmed cases cited above. ILI is rare in Illinois in August, and local health departments frequently use commercial rapid tests.
There were more than 200 ILI cases linked to the Gallia Junior County Fair and a rapid test yielded 69 cases that were influenza A positive (and testing of a subset confirmed H3N2v in 11). The 39.5% positive rate is likely near the sensitivity of this assay. The CDC recently demonstrated the poor performance of commercial rapid tests which failed to detect H3N2v when tested against purified virus which was at a level that was markedly higher than the level in most clinical samples.
Thus, it is likely that the 3 cases who tested negative were also positive (the sensitivity of the Illinois samples would then be 40%, matching the sensitivity of the rapid test in Ohio).
It is also likely that the two cases with pending results will be also positive if the samples were sent to the state lab, where PCR testing is done, which has increased sensitivity.
Today the CDC increased the number of Illinois H3N2v cases to three, but it is unclear if the announced cases were all from Coles County, or included a confirmed case in Logan County which was announced tonight in media reports.