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7 Human SIV Cases Confirmed

The Centers for Disease Control and Prevention (CDC) is reporting that seven cases of human exposure to swine influenza virus (SIV) have now been confirmed in the U.S. All of the affected people have fully recovered and none report any recent contact with swine.

Five cases have been confirmed in California and two in Texas according to information released during a CDC press conference April 23, 2009. This includes the two cases previously reported (Swine Influenza A (H1N1) Infection in Two Children with No Swine Exposure). Agency representatives indicate that it is likely that additional cases will be diagnosed as a result of routine and enhanced surveillance being conducted in response to these findings.

Preliminary genetic characterization of the influenza viruses has identified them as swine influenza A (H1N1) viruses. The viruses are similar to each other, and the majority of their genes, including the hemagglutinin (HA) gene, are similar to those of swine influenza viruses that have circulated among U.S. pigs since approximately 1999; however, two genes coding for the neuraminidase (NA) and matrix (M) proteins are similar to corresponding genes of swine influenza viruses of the Eurasian lineage (1). This particular genetic combination of swine influenza virus segments has not been recognized previously among swine or human isolates in the United States, or elsewhere based on analyses of influenza genomic sequences available on GenBank.

Viruses with this combination of genes are not known to be circulating among swine in the United States; however, no formal national surveillance system exists to determine what viruses are prevalent in the U.S. swine population. Recent collaboration between the U.S. Department of Agriculture and CDC has led to development of a pilot swine influenza virus surveillance program to better understand the epidemiology and ecology of swine influenza virus infections in swine and humans.

[Editor's note: Veterinarians and swine producers should be alert to the possibility of influenza introduction to swine herds in the U.S. and submit any suspect cases, particularly herds vaccinated against SIV, to the veterinary diagnostic lab. Anyone in contact with swine should follow normal hygiene practices, including frequent hand-washing, to minimize the risk of transmission. People experiencing flu-like symptoms are encouraged to contact their local physician and report any recent contact with swine.]

Source:
CDC Press Briefing, April 23, 2009
CDC MMWR, April 21, 2009