Washington: More than 400 schools in the US have been closed as the swine flu virus spread to 19 states, but President Barack Obama voiced hope the deadly disease will run its course "like ordinary flus".
Centres for Disease Control and Prevention (CDC) said confirmed cases have risen from 109 on Thursday to 141 on Friday with the flu now reported in 19 states, up from 11. Separately, a few states reported slightly higher numbers.
The Education Department said that 433 schools had closed, affecting 245,000 children in 17 states. That was about 100 more schools reported closed than reported on Thursday.
Meanwhile, United Airlines and Continental Airlines Inc. will temporarily cut flights to Mexico in response to lower demand amid swine flu fears.
"I'm optimistic that we're going to be able to manage this effectively," Obama told reporters as he received an update from his cabinet on the federal response to the health emergency.
At the same time, he emphasised that the federal government is preparing as if the worst is still to come so that it won't be caught flat-footed.
The most recent onset of illness was Tuesday, CDC said, indicating a continuing spread, though no faster than the rate of the regular winter flu.
"We think the cases do continue to occur," CDC's Dr. Anne Schuchat was cited as saying by the Wall Street Journal.But CDC also said the new swine flu virus lacks genes that made the 1918 pandemic strain so deadly.
Obama said it wasn't clear whether the flu would be more severe than others before it, and he said the swine flu is a cause for special concern because it is a new strain and people have not developed an immunity to it.
Government agencies are preparing in case the flu comes back in a more virulent form during the traditional flu season, the president said, talking of an overarching effort to help schools and businesses while also responding to pleas for help from other countries.
The Journal cited a US health official as saying the virus lacks genes that made the 1918 pandemic strain so deadly. The CDC said the new virus is "a very unusual" four-way combination of human genes and genes from swine viruses found in North America, Asia and Europe.