What’s going on with swine flu?

Over the last couple of days I’ve been trying to cut through the hype about swine flu. It’s been difficult because media reports are coming at a dizzying pace. Here follows the result of my attempt in Q&A format:

Is this the same swine flu that caused the 1976 scare? Although both are of the H1N1 subtype, apparently this one is different. Officials have indicated that this is a strain never before isolated. Recall that fears that the 1976 Fort Dix swine flu outbreak would morph into a pandemic were unfounded.

This virus is of the H1N1 subtype. So was the virus that caused the 1918 pandemic. Are they the same virus? No. Again, officials say this virus has never been seen before, and it has elements of three animal strains and one human strain. The 1918 pandemic virus resulted from a direct mutation of a pure avian strain.

What is the pandemic risk? The World Health Organization believes the threat of a pandemic exists. The finding of elements of three animal strains and one human strain suggests that it developed by genetic reassortment rather than a direct mutation. In the past, strains created by genetic reassortment have resulted in milder pandemics (1957, 1968) than that created by direct mutation (1918). The 1957 and 1968 strains, however, were the result of reassortment between one human and one animal strain. The new swine flu strain contains elements from three animal strains and could conceivably be more virulent than the 1957 and 1968 strains. For background information on genetic reassortment as opposed to direct mutation causing pandemic flu consult this reference.

What is the relationship between the U.S. and the Mexico cases? Of the much larger number of cases of severe influenza like illness in Mexico only a small minority are thus far confirmed as swine flu. From the WHO report:

24 April 2009 -- The United States Government has reported seven confirmed human cases of Swine Influenza A/H1N1 in the USA (five in California and two in Texas) and nine suspect cases. All seven confirmed cases had mild Influenza-Like Illness (ILI), with only one requiring brief hospitalization. No deaths have been reported.

The Government of Mexico has reported three separate events. In the Federal District of Mexico, surveillance began picking up cases of ILI starting 18 March. The number of cases has risen steadily through April and as of 23 April there are now more than 854 cases of pneumonia from the capital. Of those, 59 have died. In San Luis Potosi, in central Mexico, 24 cases of ILI, with three deaths, have been reported. And from Mexicali, near the border with the United States, four cases of ILI, with no deaths, have been reported.

Of the Mexican cases, 18 have been laboratory confirmed in Canada as Swine Influenza A/H1N1, while 12 of those are genetically identical to the Swine Influenza A/H1N1 viruses from California.

I don’t usually appeal to the popular media for perspectives in health issues but this piece by Dr. Marc Siegel seemed helpful.

Here’s more from Kevin MD.

Follow CDC Twitter updates here.

Here is CDC’s main swine flu page with additional links.

WHO information here.

Disclaimer: This post is the result of the efforts of a non-expert to make some sense of the media hype by going to primary sources. Don’t accept what I say uncritically. Check the links above. This story is changing rapidly and much of what is stated here may be wrong in a few days.