The CDC in Atlanta has become the center for the swine flu investigation. It is one of only four laboratories in the world that have the expertise to unravel a novel flu strain.
"What we're trying to do is to identify how bad, how good, the swine flu is currently operating -- is it expanding, is it contracting, is it maintaining a steady state," said Phillip Navin, director of the Division of Emergency Operations at the CDC.
With the uptick in cases, the CDC shipped out more anti-virals and sent additional teams into the field.
"I think at the moment we need to be looking forward and making sure that we're doing everything that we can to keep people from getting sick," said Dr. Steve Reed, director of the CDC's Influeza Coordination Unit.
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 Tuesday 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 Tuesday suspended its stops at Mexican ports because of its concerns about swine flu.
Around the world, New Zealand confirmed 11 cases, and Israel confirmed one Tuesday. 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.
Ten countries have restricted their imports of U.S. pork or swine, including Russia, China, Philippines, Thailand, South Korea, Kazakhstan, Serbia, Ukraine, the United Arab Emirates and Ecuador.