Source: Lisa M. Keefe, MEATINGPLACE, 12/28/11

Swine-to-human transmission of flu viruses, while still rare, appeared to increase frequency in 2011, according to an early release version of the Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report (“Update: Influenza A (H3N2)v Transmission and Guidelines — Five States, 2011”).
Since 2005, the CDC reports, only 35 cases of apparent swine-to-human transmissions of influenza have been recorded. However, from Aug. 17 to Dec. 23, 2011, the CDC received reports of 12 human infections with influenza A (H3N2)v viruses that have elements of the H1N1 viruses identified as the culprits in the flu outbreak in 2009.

The 12 cases occurred in five states (Indiana, Iowa, Maine, Pennsylvania and West Virginia), and 11 were in children. Six of the 12 patients had no identified recent exposure to swine. However, one case was an adult male in Indiana with occupational exposure to swine, and two others were children in West Virginia who regularly attended the same day care.

“When different influenza viruses simultaneously infect a single host (e.g., a human or swine), exchange of genetic material can occur, resulting in a new influenza virus. Depending on the antigenic distance between the new virus and recently circulating seasonal viruses, little or no immunity might exist in the human population,” the CDC points out in the editorial notes to its report.

The case of the swine-industry employee in Indiana “highlights the risk for interspecies influenza transmission in occupational settings where humans are exposed to swine,” the agency says. It underscores the importance of proper hygiene in the industry. In the case of the two children in day care in West Virginia, the fact that the one became ill a full 10 days or more after the other seems to indicate that one child did not infect the other; research as to the origins of those illnesses is ongoing.

Surveillance for Swine Influenza Virus in the United States is overseen by USDA. Characterization and analysis on swine-origin influenza viruses are ongoing, and new submissions are added as diagnostic work is completed.

The read the report in its entirety, click here.

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