A school assistant principal who was sick for several days with swine flu on Sunday became the city's first death linked to the virus and the nation's sixth.

Mitchell Wiener, who worked at an intermediate school in Queens, died Sunday evening, Flushing Hospital Medical Center spokesman Andrew Rubin said. Wiener, who had been hospitalized and on a ventilator, had been sick with the virus for nearly a week before his school was closed on Thursday. Complications besides the virus likely played a part in his death, Rubin said.

Mayor Michael Bloomberg said the death of Wiener, who had taught for decades, "is a loss for our schools and our city."

"He was a well-liked and devoted educator," Bloomberg said in a statement.

Wiener was hired as a substitute teacher in March 1978, then as a mathematics teacher, working in that position until 2007. Since then, Wiener had been employed as an assistant principal at I.S. 238, also known as the Susan B. Anthony Intermediate School, in the Hollis neighborhood.

Besides Wiener, no one else in New York City has become seriously ill from the virus. As of Sunday afternoon, health officials had reported five other deaths in the U.S.: three in Texas, one in Washington state and one in Arizona.

Most people sickened from the swine flu, or the H1N1 virus, have complained of mild, seasonal flu-like symptoms such as fever, cough, sore throat, body aches and fatigue.

The city's first outbreak of swine flu occurred three weeks ago, when about 700 students and 300 other people associated with a Catholic high school in Queens began falling ill following the return of several students from vacations in Mexico, the epicenter of the outbreak. The school was closed.

Five more city schools were to close Monday because of concern for swine flu, bringing the total to 11, including Wiener's.

City health officials announced Sunday that four Queens public schools and one Catholic school would close for up to five school days. Three of the public schools are in the same building in Flushing. Each school had students with flu-like illness last week.

The latest school closings will affect nearly 3,000 students. Schools will be providing curriculum material online, and parents will be able to pick up materials at schools and other locations, schools Chancellor Joel Klein said.

There were no documented cases of swine flu at any of the schools, said Jessica Scaperotti, a spokeswoman for the city's Department of Health and Mental Hygiene.

The health department said it is monitoring unusual clusters of flu cases as it works to stop the spread of the swine flu virus.

"We are now seeing a rising tide of flu in many parts of New York City," Health Commissioner Thomas Frieden said in a statement. "With the virus spreading widely, closing these and other individual schools will make little difference in transmission throughout New York City, but we hope it will help slow transmission within the individual school communities."

The school where the virus was first reported, St. Francis Preparatory, has been cleaned and reopened, and many New Yorkers had assumed before the latest flurry of school closings that the danger of swine flu was subsiding.

But Dr. Scott Harper, an epidemiologist with the health department, said health officials weren't surprised by the continued presence of the virus.

"It's so unpredictable," Harper said.

As of the weekend, there were 178 confirmed swine flu cases in New York City, Harper said, but the number of actual cases is believed to be much higher.

Health officials urged people with underlying health conditions to see their doctors if they believe they may have been exposed to swine flu. That includes people with diabetes, people whose immune systems are compromised because of certain cancer medications, pregnant women, elderly people and infants.