CDC Tracks Rise of Swine Influenza in Humans

The U.S. Centers for Disease Control and Prevention (CDC) have reportedly noted an increase in rare human swine influenza infections, documenting two similar cases in California children not directly exposed to livestock. The agency stated that it typically registers one human swine influenza case every year or two in the United States, but has verified 12 infections between December 2005 and February 2009. CDC also confirmed seven additional cases in Texas and California during March 2009, describing a unique influenza strain that combines segments of a human virus, an avian virus from North America, and pig viruses from North America, Europe and Asia. In addition, Mexican health officials have reported that a swine influenza outbreak recently killed 16 people, including children and young adults, and sickened as many as 943 in the Mexico City area.

Meanwhile, the World Health Organization and other experts have expressed concern that the cases, if related, could trigger a pandemic. According to CDC, “this new strain of swine influenza A (H1N1) is substantially different from human influenza A (H1N1) viruses, that a large proportion of the population might be susceptible to infection, and that the seasonal influenza vaccine H1N1 strain might not provide protection.” The agency has advised clinicians in California and Texas to consider animal as well as seasonal influenza in patients presenting with febrile respiratory illness. “The lack of known exposure to pigs in the two cases increases the possibility that human-to-human transmission of this new influenza virus has occurred,” said the CDC, which in 1976 tracked a human swine influenza outbreak that shared viral characteristics with the 1918-19 worldwide epidemic. See MMWR Dispatch, April 21, 2009; MSNBC.com, April 21 and 24, 2009; Reuters, April 24, 2009.