An outbreak caused by a novel strain of H1N1 influenza, commonly called "swine flu", began in Mexico in March 2009 and spread rapidly to many other countries. The virus contained a unique combination of swine, avian, and human influenza gene segments that had not been previously observed. Initial reports from Mexico indicated a high fatality rate in previously healthy young adults and older children, raising concerns that a worldwide pandemic might occur, similar to 1918. However, subsequent data from Mexico, as well as experience from other countries, indicated the H1N1 strain from 2009 is not nearly as lethal as some people initially feared. As of June 29, 2009, a total of 70,893 cases and 311 deaths had been reported from more than 100 countries, though the true number of cases is undoubtedly much higher. Of these, 8279 cases and 116 deaths were reported from Mexico, 27,717 cases and 127 deaths were reported from the United States, and 7775 caes and 21 deaths occurred in Canada.
Preliminary data indicate that up to one-third of those greater than 60 years of age have antibodies against the novel H1N1 virus, whereas protective antibodies are found much less frequently in children and younger adults (see MMWR). This is consistent with the clinical experience so far, which indicates that the most severe cases are occurring in those who are younger than age 60.
The World Health Organization does not recommend any travel restrictions at this time. To protect yourself from H1N1 influenza, wash your hands regularly and avoid close contact with anyone who is coughing or sneezing. Routine use of face masks is not recommended. The symptoms of H1N1 influenza include fever, cough, sore throat, body aches, headache, chills and fatigue, similar to seasonal influenza. Any traveler who develops flu-like symptoms after travel to a country which has reported H1N1 influenza should immediately seek medical attention. Clinicians who suspect H1N1 influenza virus infections in humans should obtain a nasopharyngeal swab from the patient, place the swab in a viral transport medium, and contact their state or local health department to facilitate transport and timely diagnosis at a state public health laboratory. In the test tube, the virus appears to be susceptible to oseltamivir (Tamiflu) and zanamivir (Relenza), but resistant to amantadine and rimantadine. Empiric treatment with Tamiflu or Relenza should be considered for suspected cases. It is not anticipated that the influenza vaccine given in the winter of 2008-2009 will be protective against this virus. For further information on novel H1N1 influenza (swine flu), go to the World Health Organization and the Centers for Disease Control.
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