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Ebola Virus explained


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CDC study suggests many H3N2v cases may be missed

An investigation of one of the first swine-origin H3N2 influenza cases detected in the United States in 2011 suggests that for each confirmed case, there may be many more that go undetected.

The investigation, triggered by a case related to a Pennsylvania fair in August 2011, revealed 3 confirmed cases, 4 probable cases, and 82 suspected cases of variant H3N2 (H3N2v), all of them in people who had attended the fair, according to a report published yesterday in Emerging Infectious Diseases.

The virus could not be confirmed in most cases because most of those with suspected infections had recovered before the investigation, the report says. But among six children under age 4, an age-group in which retrospective serologic testing for novel flu viruses is more useful than for older groups, four tested positive for antibodies to the virus.

"This finding suggests that illness in at least some suspected case-patients can be attributed to A(H3N2v) virus infection," says the report by investigators from the Centers for Disease Control and Prevention (CDC), the Pennsylvania departments of health and agriculture, and the Allegheny County Health Department in Pittsburgh.

The investigators also found signs that greater exposure to pigs increased the risk of having a suspected case, though this finding was not statistically significant. They found no clear evidence of efficient or sustained human-to-human transmission of the virus.

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