A New Patient Zero*

Mexico has confirmed that a person from Mexico City infected with the swine flu virus developed symptoms on 11 March, 6 days earlier than a case that many in the media dubbed “patient zero,” ScienceInsider has learned. The finding not only adds a new entry to the left end of the outbreak’s timeline, but it also calls into question the geographical link between the former patient zero and a huge pig farm.

Epidemiologist Mauricio Hernández-Ávila, the vice minister of disease prevention and health promotion for Mexico's Ministry of Health, stressed to ScienceInsider that the Mexican labs still have many older samples to test. “My guess is that we will have some earlier cases, and we are working on that,” said Hernández-Ávila, noting that they have other untested samples from early March and possibly February.

The previous patient zero, a 4-year-old boy from La Gloria in Veracruz state, lived near a huge hog farm in Perote, Granjas Carroll, that some suspected may have housed an infected pig that kick-started the outbreak. But testing has not found a pig infected with what’s now called the 2009 A (H1N1) influenza virus, nor have any farm workers tested positive.

Hernández-Ávila says he remains open-minded about the origin, and it may eventually point back to the Perote region when they do more testing. “It is remarkable that in a such a small community, which is isolated, that we have one swine-flu-positive person,” he says.

* Warning: Likely to change.