In the past several weeks, there has been an outbreak of illness in Mexico and the U.S. caused by a new strain of influenza virus that contains a combination of swine, avian, and human influenza virus genes. The illness has killed many patients, and the outbreak has features that suggest it could become a global pandemic. Federal officials have responded by declaring a public health emergency in the U.S., freeing up new resources for the prevention, diagnosis, and treatment of the disease.

Pigs, birds, and humans are each susceptible to lots of influenza viruses. Typically, these viruses infect only one species. However, sometimes the viruses swap genes, creating new viruses that have the capacity to infect more than one species. Even then, new viruses capable of infecting two species typically are very hard to transmit from human to human. Sometimes, however, further recombinations or mutations of genes create a virus that can spread rapidly among humans — creating a global pandemic. The worst global pandemic in modern times was the pandemic of 1918–19. It affected about a third of the human race, and killed at least 40 million people in roughly a year — more than have been killed by AIDS in three decades.

The World Health Organization and the CDC have confirmed that the new swine flu virus is transmitted between humans. It is not clear yet how transmissible it is, nor how it is transmitted. Almost surely, like other flu viruses, it can be transmitted by aerosol and by skin-to-skin contact with an infected person.

As of this writing, about 100 deaths have been attributed to the virus — all in Mexico. The 20 confirmed cases in the U.S. have all recovered (with only 1 case requiring hospitalization). Ominously, many of the deaths in Mexico seem to have occurred in healthy young adults, a pattern seen in past pandemics — not young children and the frail elderly, as is most often seen with the flu. It remains uncertain what the mortality rate is in Mexico and why the illness appears to be milder so far in the U.S.

The new virus is resistant to amantadine and rimantadine, but sensitive to oseltamivir (Tamiflu) and zanamivir (Relenza). Based on experience with other flu viruses, treatment would be most effective if given within two days of the onset of symptoms. Obviously, there is no vaccine yet for the new virus, and the CDC has expressed doubt that the current flu vaccine will offer protection.

The initial symptoms with this swine flu virus are like those with the annual flu viruses: fever, myalgias, rhinorrhea, and sore throat. Nausea, vomiting, and diarrhea may be more common with this flu than with regular flu. The usual precautions for patients apply:

• Sneeze and cough into tissues and throw the tissues in the trash.
• Wash your hands or use alcohol-based hand cleaners frequently.
• On greeting people, don’t shake hands or exchange kisses.

People should be considered contagious until at least 7 days after the start of symptoms; with children, it may be 10–14 days. Patients can be reassured that they cannot get swine flu from eating pork.If a global pandemic ensues, governments may well close schools and public places, require as many people as possible to work from home, warn any people who develop symptoms to isolate themselves at home, and warn those with symptoms indicating more severe disease (particularly breathlessness) to seek medical attention immediately. Journal Watch will update you regularly as new information is available.Updated information from the CDC is available at   http://www.cdc.gov/swineflu/.Published in Journal Watch General Medicine April 27, 2009.

Comment: This is an excellent summary of where we stand today. Unfortunately we maybe at the brisk of an epidemic_BA