In scores of schools across the United States, the mop has been the weapon of choice in the fight against swine flu.
When hundreds of children fell ill with the virus at a Queens high school last month, authorities promptly closed the building and spent days disinfecting desks and tables and running the ventilation system on full blast.
Alarmed union officials called for the same response — evacuation and a vigorous scrub-down — when flu cases popped up this week at the city's massive jail complex on Rikers Island.
But while such cleansing efforts are undoubtedly reassuring to the public, they probably do little to control the spread of the disease, health experts said.
"It never hurts to be cleaner," said the city's health commissioner, Dr. Thomas Frieden, "but the main way flu spreads is people not covering their mouth or nose when they cough or sneeze."
As frightening as it can be, the influenza virus is not a hardy one. Once it leaves the body of an infected person, it usually dies within a few hours.
Any surface left alone for 24 hours is unlikely to have influenza, said Dr. Paul Biddinger, associate director of the Center for Public Health Preparedness at the Harvard School of Public Health.
"Plus, you can wipe down the surfaces today, and then someone comes in coughing and sneezing and you're infected again," he said. "Unless you are willing every hour and every day to wipe down surfaces, it isn't going to do much good."
The mop's relative ineffectiveness in halting the spread of the swine flu virus is illustrative of a larger problem facing public health authorities trying to contain the infection: Outside of developing a vaccine, there isn't much that can be done to halt the bug's spread.
Authorities have cautioned doctors against trying to ward off infection by prescribing antivirals such as Tamiflu, warning it could deplete the supply of the medication before they know whether the epidemic is serious or could give rise to a drug-resistant form of the virus.
In the U.S., public health officials have rejected restrictions on travel and public gatherings as draconian and probably worthless, now that the virus has spread worldwide.
"Nobody wants to see a repeat of overreacting when there is no real emergency," said Dr. Stephen S. Morse, professor of clinical epidemiology at the Mailman School of Public Health at Columbia University, citing the government's rush to inoculate people during a swine flu scare in 1976.
Some cities have reacted to outbreaks by closing schools. But even that step is questionable, experts said.
"As a disease containment measure, it is not likely to be effective," said Biddinger.
In most cases, he said, shutting a school once children have gotten ill means authorities have acted too late to halt the spread.
The U.S. Centers for Disease Control and Prevention initially advised school systems to close if outbreaks occurred, then reversed itself, saying the apparent mildness of the virus meant most schools and day care centers should stay open, even if they had confirmed cases of swine flu.
Experts have studied all sorts of other methods of trying to control flu infections, from bathing hospital waiting rooms in ultraviolet lighting for eradicating germs to using aerosolized saline droplets to interrupt transmission. Nothing has proven effective enough to try on a large scale.
The best defense, repeated again and again by doctors in recent weeks, is for people to wash their hands frequently, avoid touching their eyes, noses and mouths, cover their mouths when they sneeze or cough and stay home if they feel ill.
"You've heard this a million times," Morse said, "but it's good advice."
Flu is thought to be transmitted primarily through saliva or other bodily fluids, meaning people are most likely to get it if they kiss or share eating utensils with infected people.
Among people in less close contact, it is spread by the droplets that spray from people's mouths when they cough or sneeze.
Those particles usually travel less than 6 feet and don't remain suspended in the air. Once they land, the virus generally loses its ability to infect anyone after a few hours.
That doesn't mean that schools, airline crews or parents with sick kids at home should stop disinfecting surfaces, said Morse.
"I think those are good things to do. They are just the things our grandmothers told us, and I think we should do them on a daily basis," he said, noting that scrub-downs are effective against plenty of other longer-living viruses, like the one that causes the common cold.
As for containing the virus in the nation's biggest city, Mayor Michael Bloomberg suggested Tuesday that resistance was futile.
"This is one of those things that we just have to live with," he told reporters. "It will make its way through the population, probably every country, and certainly on every continent, and probably through this crowd right here."