A month after swine first appeared on the global health scene, a growing number of schools in New York, Houston and Boston have shut their doors as health officials take measures to contain its spread among students.
The school closures underscore the fears surrounding the novel variant of the H1N1 virus -- a pathogen to which few in the world have immunity, health officials have said.
As of Wednesday morning, there were 26 schools closed in New York, 10 more than on Monday, and another school in New Jersey was shut down because of tensions about the new virus.
The closings appear to be having an effect on the city's overall school attendance rates. In what Department of Education officials call a "significant drop," on Tuesday only 85.5 percent of New York City's 1.1 million students were present, compared with 88.5 percent a week before. In Queens, only 83.2 percent of students were present for school on Tuesday.
With the closures come more evidence of worry among the public -- at least in these cities. Even as New York health officials said the Monday death of a 16-month-old toddler who had flulike symptoms did not have swine flu, hospital emergency rooms in the city filled with concerned parents and sick children. At Elmhurst Hospital -- the same medical center where young Jonathan Zamora of Queens was admitted with flulike symptoms and later died -- more than 400 people crowded the emergency department on Tuesday alone.
Hospitals in other cities around the country have reported no similar surge in their emergency departments, with only a few noticing a modest uptick in patients with flulike symptoms.
However, the story is a far different one in New York City. St. Luke's-Roosevelt Hospital Center reported that it served 476 patients in its emergency department Tuesday -- a new record. Bellevue Hospital Center noted a "massive influx of patients" and "substantial delays" in its emergency department, and SUNY Downstate Medical Center said it had a large increase in traffic in its pediatric emergency room.
The new tensions about the outbreak come days after the city's first confirmed death of a patient with swine flu. Late Sunday, 55-year-old assistant principal Mitchell Wiener became the sixth American to die from complications of the swine flu.
On Monday, New York officials closed 16 schools after 103 students in four schools came down with influenza-like symptoms in the past week.
Health officials say they are not surprised by swine flu's tenacity.
"In fact, it has been taking off," Dr. Scott Harper of the New York City Health Department told "Good Morning America" today. "That's what we were expecting to see eventually, because that's what influenza does."
Swine Flu's Severity Still Uncertain
Federal health officials agree that it's still not clear how bad swine flu really is.
"The illness severity that we're seeing is still similar to what we've seen with seasonal influenza," Dr. Anne Schuchat, director of the U.S. Centers for Disease Control and Prevention's National Center for Immunization and Respiratory Diseases, said Monday at a press conference. "I think our best estimate right now is that fatality is likely a little bit higher than seasonal influenza, but not much higher."
Despite that, the new virus may be contributing to higher than normal levels of flu infections in general for this time of year -- as well as more school-based outbreaks, which Schuchat said are unusual for springtime.
"About half of what we're seeing lately is the novel H1N1 strain," she said.
But health officials still warn that the situation could change quickly, particularly if the virus were to mutate.
"One of the concerns that we have is the virus could change and that it in fact could cause more severe illness," Harper said. "We don't think that's the case right now, but we know that influenza viruses do change frequently."
Worldwide, health officials are identifying more cases. According to World Health Organization statistics released Wednesday morning, 10,243 cases of swine flu have now been identified in 40 countries, and 80 of those infected have died.
Yet prominent infectious disease experts say that even if the WHO raises the pandemic alert from 5 to 6 -- the highest level -- the formal classification is not likely to sway future public health response. Governments and health officials would likely take the same course of action as they are presently, the experts said.
A vaccine for the virus is currently in the works. However, WHO officials have said that drug manufacturers won't be able to start making a vaccine until mid-July at the earliest. They attribute the delay to the fact that the virus does not appear to grow quickly in a laboratory setting, making it difficult for scientists to get a key vaccine ingredient.
When to See the Doctor for the Flu
While experts search for signs of how deadly the swine flu may become on a global scale, family physicians and emergency medical doctors say patients at home are in the same quandary: how to tell if this flu will pass as usual or turn serious and deadly.
"People who are walking around with a normal-grade fever shouldn't be going to the emergency room for treatment, even though they are," said Dr. Andrew Sama, a member of the American College of Emergency Physician's board of directors.
Sama said the majority of flu cases can be treated at home or with a phone consultation, or a visit to the family doctor.
In the most severe cases, Sama said patients will be shuttled off to the intensive care unit to protect against respiratory failure. He said most people survive, "But generally speaking not everyone who is on a respiratory ICU treatment can be saved."
"Generally speaking, only people who are really ill from the flu -- nonstop vomiting, extremely high fever, inability to eat and drink, excessive weakness, chest pain, severe cough, lethargy, trouble breathing -- should come in," he said.
However, Sama and Dr. Lori Heim, the president-elect of the American Academy of Family Physicians, said three specific groups of people should go to the doctor with much less severe symptoms: children under age 4 with a high fever, people with compromised immune systems and the elderly.
"If you're one of the lucky people in the country who has a regular physician, calling them would be my first choice," Heim said. "But if you can't breathe, don't wait for a phone call back."
ABC News' Rich Esposito and reports from The Associated Press contributed to this report.