(AP) -- A day after a swine flu outbreak shut down three public schools in New York City, officials said Friday the virus is spreading faster than seasonal flu does, but the symptoms have generally been mild.
Health Commissioner Dr. Thomas Frieden said the large clusters of cases at the three schools are "a little surprising," and officials don't know why the virus is spreading more rapidly than traditional influenza. Hundreds of schoolchildren were sent home sick this week and an assistant principal remains in critical condition.
The schools were closed Thursday after four students and the assistant principal at the Susan B. Anthony middle school in Queens were confirmed to have swine flu. Mayor Michael Bloomberg said there were no immediate plans to close more schools.
The Centers for Disease Control and Prevention has said repeatedly that there would be more deaths and new cases, and that the strain was still on the upswing in the U.S. Texas on Friday reported the nation's fifth swine flu death.
The mayor said Thursday that the assistant principal, Mitch Wiener, may have had pre-existing health problems - but on Friday, Wiener's son Adam said his father had only suffered previously from gout, which he said was unrelated to his current condition. He said his 55-year-old father is now suffering from pneumonia, kidney failure, dehydration and a lung infection.
"We're dealing with it the best way we can but it's obviously hard," said Adam Wiener, 23. "They say it's critical but not hopeless."
It isn't unusual for flu cases to ebb and surge as the virus moves through a population during flu season. The virus tends to disappear as the weather gets warmer and more humid.
Dr. Isaac Weisfuse, a deputy commissioner of the health department, said investigators are trying to learn more about why the disease has spread erratically.
Schools are a good incubator for illness in general, he said, because space is tight and youngsters often don't practice the best hygiene.
Adam Wiener said his father had been sick since at least last weekend with flu-like symptoms "but we didn't think anything of it." Then early Wednesday, he said, the family called 911 after his father began "hallucinating and wasn't coherent."
Wiener's case is the most severe illness in the city since its first known cases of swine flu appeared in late April. At least five schools in the city were closed then, but all have since reopened.
Frieden said Friday that officials look at a number of factors when deciding whether to close a school, including how many kids are out sick. "It has to be a school-by-school and day-by-day assessment," he said.
Meanwhile, maintenance workers at the two middle schools and one elementary school scrubbed desks, floors and door handles Friday.
At the shuttered Walter Crowley middle school in the Elmhurst section, a worker in a mask was seen mopping down the cafeteria on Friday. Police cars were parked outside the entrances, and a sign on the door said it was temporarily closed. At that school alone, 241 students were reported out sick with flulike symptoms.
New York City's first outbreak occurred when hundreds of teenagers at a Roman Catholic high school in Queens began falling ill following the return of several students from vacations in Mexico, where the outbreak began.
An estimated 1,000 students, their relatives and staff at the St. Francis Preparatory School fell ill in a matter of days.
Additional sporadic cases continued to be diagnosed, but the symptoms were nearly all mild. The sick children recovered in short order and St. Francis reopened after being closed for a week. The middle school with the confirmed cases is two miles from St. Francis.
Adam Wiener said his father has been mostly unconscious because of sedation since Wednesday evening, breathing with the help of a ventilator.
One of Wiener's 18-year-old twin sons, Jordan, said his father had been awake briefly and asked him about his leg, which he had injured playing baseball.
"He's always about his kids first," Jordan Wiener said Friday. "He was asking me how I was feeling and how my season's going."
Associated Press Writer David B. Caruso contributed to this report.
©2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.