The H1N1 virus has spread throughout most of the country, and health officials said Sunday that they expect more severe cases and deaths from what's commonly called swine flu.
Doctors at the Centers for Disease Control and Prevention (CDC) expressed caution about the outbreak even as Mexican health officials said that the new flu strain appears to have peaked, with fewer cases overall and fewer people being hospitalized.
Mexico has 506 confirmed flu cases and 19 deaths. Worldwide, tests confirm 898 cases of swine flu in 18 countries and 20 deaths, according to the World Health Organization (WHO).
"Virtually all of the United States has this virus circulating now," said Anne Schuchat, CDC interim deputy director for science and public health programs. "I expect the number to jump quite a bit in the next few days."
On Sunday, doctors had confirmed 226 cases in 30 states, up from 21 states the day before. Cases will rise as labs work through their backlog of specimens waiting to be tested, Schuchat said in a briefing.
The CDC has sent test kits to all of the states to allow them to confirm specimens themselves. The CDC now will focus less on testing and more on measuring whether the outbreak is waxing or waning. Schuchat said the virus appears to cause mostly mild forms of the flu.
Doctors are concerned about what the virus will do in the fall. The 1918 flu pandemic, which killed 50 million people worldwide, began in the spring, became dormant in the summer and roared back in the fall, said WHO spokesman Gregory Hartl.
However, the CDC's Nancy Cox said tests show that H1N1 does not appear to carry the same markers for aggressiveness found on the 1918 virus.
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