The biggest increase occurred in New York City where the number of cases leaped from 28 to 45, the CDC said.
Mayor Michael Bloomberg said Monday the cases were confined to a "single cluster," students of St. Francis Preparatory School and their relatives. Several of the students had spent spring break in Cancun, Mexico, which health officials suspect is the origin of the outbreak.
But Bloomberg said today that it appears to have spread to at least one other school, Public School 177, a school for autistic children. Of PS 177's 380 students, 82 called in sick today and at least a dozen have fevers. One of those students has two siblings at St. Francis Prep, Bloomberg said. Both of the those schools are located in the borough of Queens.
The mayor also said there are six possible cases of the flu in a Manattan school, Ascension parochial school.
And New York City Health Commissioner Thomas Frieden said today that "many hundreds" of students and teachers at St. Francis are sick -- though most of those cases appear mild so far.
"It is here and it is spreading," Frieden said. "We do not know whether it will continue to spread."
At one point the Ernst and Young corporation said it had confirmed a case at its Manhattan headquarters, but later retracted the statement.
In addition, there were four more cases in Texas and three additional cases in California.
Leaders in Congress raced each other to hold hearings on the outbreak. Sen. Tom Harkin of Iowa, chairman of the Senate appropriations subcommittee that deals with pandemic preparedness, called an emergency hearing to address funding for states and federal government
Sen. Joe Lieberman, I-Conn., called another hearing for Wednesday and Rep. Henry Waxman, D- Calif., the chairman of the House Energy and Commerce Committee called for a hearing on Thursday.
Concern among travelers was so great that Carnival Cruises today suspended its stops at Mexican ports because of its concerns about swine flu.
Concern about swine flu was spreading globally.
Around the world, New Zealand confirmed 11 cases, and Israel confirmed one today. South Korea, Australia and the Czech Republic announced several suspected cases.
A South Korean Catholic nun traveling in Mexico has tested positive for swine flu, according to reporting by ABC's Joohee Cho. South Korean authorities believe the 51-year-old woman caught the disease from a taxi driver and have requesting the Mexican government look into the matter.
South Korea and Ukraine have temporarily banned all pork imports from North America in response to flu concerns.
Korean health authorities are examining 315 other passengers that were on the same flight with the nun and have already injected Tamiflu into eight passengers who sat near her.
Spain had one previously confirmed case, the United Kingdom, two and Canada, six. France is still testing some people and some test results in Germany came back negative.
Most of the individuals involved had recently returned from Mexico.
To slow the global spread of the virus, the U.S. State Department and the European Union's health commissioner recommended avoiding nonessential travel to Mexico.