Commonly known as swine flu, the outbreak has sickened 9,830 peopleand caused at least 79 deaths -- mostly in Mexico, the organizationsaid. The actual number of people affected may be higher, as it takestime for national governments to confirm cases and report them to theglobal body.

In the United States, at least 5,469 cases of swineflu have been reported, according to the latest figures from theCenters for Disease Control and Prevention. The CDC has linked sixdeaths to the outbreak; health officials in New York have connected aseventh death to the disease.

Concern about the disease deepenedTuesday, even as authorities have said that the outbreak may prove tobe less severe than first suspected.

A 42-year-old man diedTuesday in suburban St. Louis, Missouri, according to John Shelton ofthe St. Louis County Health Department. The man, whose name was notreleased, had been hospitalized for the past few weeks. He had visitedMexico and tests showed he had swine flu, Shelton said. However, thecounty medical examiner will determine the cause of the man's death.

In New York, medical investigators were looking into the death of ababy boy whose mother brought him to Elmhurst Hospital. The16-month-old arrived at the hospital with a fever around 9:30 p.m.Monday and died about 50 minutes later, said said Dario Centorcelli, ahospital spokesman. The cause of death was not immediately known. Thebaby's 3-year-old sister and 1-year-old cousin were treated andreleased, Centorcelli said. Watch more about the death »

That death comes a day after an assistant principal from New York died after contracting the H1N1 virus.That man -- Mitchell Wiener -- had an underlying health condition, saidDr. Thomas Frieden, New York City's health commissioner and PresidentBarack Obama's pick to lead the CDC.

Don't Miss Poll: Concerns over H1N1 virus ease New hope for development of H1N1 vaccine5 more NYC schools close on flu fearsWHO reports big jump in swine flu casesHong Kong hotel guests freed from flu quarantine Wiener died Sunday evening of complications of the H1N1 virus, hospital and state officials said.

If confirmed by the Centers for Disease Control and Prevention,Wiener's death would be the seventh linked to swine flu in the UnitedStates. The CDC has confirmed three in Texas, two in Arizona and one inWashington state.

Wiener's school is among a handful in New YorkCity that temporarily closed at the recommendation of the city's HealthDepartment.

Frieden said Sunday that "with the virus spreadingwidely," closing affected schools "will make little difference intransmission throughout New York City, but we hope will help slowtransmission within the individual school communities."

The flu strain, which originated inMexico, killed dozens of people there, causing U.S. officials to worrythat it could take a similar toll after spreading across the border.

So far, however, it has acted similar to typical seasonal influenza --which usually can be treated successfully but can be deadly among thevery old, very young and people with pre-existing health problems.