Health officials of the US state of Illinois said on Saturday that they had confirmed 421 cases of A/H1N1flu in the state, and Saturday's tally from the Illinois Department of Public Health is 28 more than Friday's total.

In an effort to halt the spread of the flu, officials in Chicago have announced the closing of a school on the city's far north side because of high absences, although a schools spokeswoman said she could not say whether there was a confirmed flu case in a student or employee at the school.

In Illinois and other US states, the number of confirmed cases has grown quickly in recent days as a backlog of samples from probable cases has been dealt with.