(CNN) -- The number of confirmed H1N1 flu cases worldwide surpassed 10,000, the World Health Organization said Tuesday.
In the United States, at least 5,469 cases of swine flu have been reported.
Commonly known as swine flu, the outbreak has sickened 10,176 people and caused at least 80 deaths, mostly in Mexico, the organization said. The actual number of people affected may be higher, as it takes time for national governments to confirm cases and report them to the global body.
In the United States, at least 5,469 cases of swine flu have been reported, according to the latest figures from the Centers for Disease Control and Prevention. The CDC has linked six deaths to the outbreak; health officials in New York have connected a seventh death -- a school official -- to the disease.
Concern about the disease deepened Tuesday, even as authorities have said the outbreak may prove to be less severe than first suspected.
A 44-year-old man died Tuesday in suburban St. Louis, Missouri, according to John Shelton of the St. Louis County Health Department. The man, whose name was not released, had been hospitalized for the past few weeks. He had visited Mexico and tests showed he had swine flu, Shelton said. However, the county medical examiner will determine the cause of the man's death.
In New York, medical investigators determined that the death of a 16-month-old boy in Queens was not linked to the flu. The boy had a fever when his mother brought him to a hospital Monday and he died less than an hour later, drawing attention from investigators.
That death came a day after an assistant principal from New York died after contracting the H1N1 virus. That man -- Mitchell Wiener -- had an underlying health condition, said Dr. Thomas Frieden, New York City's health commissioner and President Barack Obama's pick to lead the CDC.
Wiener died Sunday of complications of the H1N1 virus, hospital and state officials said.
If confirmed by the CDC, Wiener's death would be the seventh linked to swine flu in the United States. The CDC has confirmed three in Texas, two in Arizona and one in Washington state.
Wiener's school is among a handful in New York that temporarily closed at the recommendation of the city's Health Department.
Frieden said Sunday that "with the virus spreading widely," closing affected schools "will make little difference in transmission throughout New York City, but we hope will help slow transmission within the individual school communities."
The flu strain, which originated in Mexico, killed dozens of people there, causing U.S. officials to worry that it could take a similar toll north of the border.
So far, however, it has acted similar to typical seasonal influenza, which usually can be treated successfully but can be deadly among the very old, very young and people with pre-existing health problems.
CNN's Kara Devlin and Mary Snow contributed to this report.