From this:

Mexico's chief epidemiologist (Dr. Miguel Angel Lezana, director of the National Epidemiology Center) accused the World Health Organization of being slow to respond to the country's warning about a health crisis that turned into a global swine flu scare and called for an investigation.

[He] told The Associated Press late Thursday his center alerted the Pan American Health Organization on April 16 about alarming occurrences of flu and atypical pneumonia in Mexico. But no action was taken until eight days later when the World Health Organization said it was "very, very concerned" the outbreak could grow into a pandemic...

PAHO spokesman Daniel Epstein confirmed to The Washington Post that the agency got a message from Mexican authorities on April 16 about an unusual disease outbreak.

Epstein, who is with PAHO's Washington office, told the newspaper that it was impossible for authorities in Geneva not to have learned of the unusual outbreak at the same time, describing a system that sends messages through to WHO headquarters automatically.