"Prediction is very difficult, especially if it's about the future." -Niels Bohr
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If you have followed Minnesota news media this week, you may be confused about pigs, fairs and influenza. On Monday, I recommended that county, regional and state fairs throughout North America eliminate swine exhibits for the remainder of the year owing to the threat of transmission of the novel influenza virus strain H3N2v, from pigs to other pigs and to humans.
State public health officials disagreed, citing the low risk for such infections to occur, particularly given steps to screen out sick pigs from coming to the fair and the increased attention to hand-washing. This is more than a scientific disagreement; it has potentially important public health implications.
To understand what's at stake, a bit of background will help. Dating back to Hippocrates, influenza has been one of the "lion kings" of infectious diseases. Influenza is caused by a respiratory virus and almost always is spread by humans to humans. The symptoms include fever, cough, muscle aches and just plain feeling horrible.
Influenza occurs in two different patterns: annual seasonal epidemics during our winter months or global pandemics, which can occur during any season and last more than a year. An estimated 3,000 to 49,000 individuals in the United States die every year from seasonal influenza, and thousands more require hospitalization for influenza-related disease.
Influenza pandemics occur when novel influenza viruses in animals undergo genetic changes that allow the viruses to infect humans and in turn humans to transmit the new human-adapted virus to others. Four pandemics have occurred in the last 94 years: 1918, 1957, 1968 and 2009.
Influenza pandemics can vary in severity; in 1918, an estimated 50 million to 100 million people died worldwide. In the 1957 and 1968 pandemics, an estimated 1.5 million and 750,000 people died, respectively. An official estimate of worldwide deaths from the 2009 pandemic is not expected until later this year.
