The new year came in with a bang – at least in offices that have been hit hard by flu and other viral infections.

This year’s round of runny noses, coughs, and upset stomachs has been working its way across the city, leaving few workplaces and classrooms untouched. The symptoms started between three weeks and a month ago, according to health professionals, and since then, illnesses have been running rampant.

Stricken workers are suffering on two fronts: respiratory infections and bouts of diarrhea and vomiting, according to the chairman of the Department of Medicine at Beth Israel Medical Center, Stephen Baum, an infectious disease physician.

Even flu shots, for those who could get them, cannot prevent many of these illnesses, which, despite flu-like symptoms, are caused by between 50 and 100 different viruses other than influenza.

The Department of Health recently reported an uptick in visits to emergency rooms, a rise in sales of cold medicines at pharmacies, and more doctor appointments.

The director of the infectious-diseases section of New York Hospital Queens, James Rahal, said holiday gatherings may have contributed to the recent sicknesses.

“People have been getting together. They go to parties. They travel on airplanes,” Dr. Rahal, who is professor of medicine at Weill Medical College, said yesterday.

“The first week in January, people seem to have more illnesses,” he said, “which follows our getting together for the holidays, which may not be a healthy thing.”

One sufferer, Tom O’Connor of Murray Hill, said he has been feeling under the weather lately.

“I have a lingering cold, like half the population of New York right now,” Mr. O’Connor, 68, said, standing outside the Reade Street Pub and Kitchen in TriBeCa. “Everybody’s sick. We’re the walking wounded…. It’s a bug that’s going around. Most people I know have had it for two weeks running.”

Mr. O’Connor said, however, that his illness is not the flu – because with the flu, “You can’t move.”

Mr. O’Connor, an employee at the city Department of Correction, said several co-workers had been out sick during and after the holidays.

Earlier in the holiday season, a lawyer from the Upper East Side, Melvin Dubinsky, was similarly afflicted, but, in the middle of a big case, he didn’t have the luxury of taking it easy.

“Usually I try to get over colds myself,” he said. “I do all the things they taught us in the Army. I keep warm, get a lot of rest, and drink a lot of fluids. Usually that works for me. But this time I couldn’t get enough rest because of the ongoing trial, so to take more precautions I went to the doctor.”

Mr. Dubinsky’s doctor told him that he missed his chance to get a flu shot since he was already sick, but after some antibiotics he recovered quickly.

“The holidays do have an effect,” the chairman of medicine at NYU Medical Center, Martin Blaser, said.

Dr. Blaser, who is president-elect of the Infectious Disease Society of America, said one of the causes of sickness in schools and workplaces is taking an otherwise stable community and introducing germs picked up from mixing with people from all over the country who may have visited during the holidays.

“The single most important thing is to wash your hands a lot,” Beth Israel’s Dr. Baum said. The same advice holds true for children, but “it’s probably not going to be followed,” which is why schools tend to be “breeding grounds for infection,” he said.

An associate professor of medicine at Cornell University, internist Keith Roach, said he made it through the first four or five years of being a doctor without catching a single cold – until he had his three kids. At school, germs spread from child to child through touch, Dr. Roach said, “and then they come home and give them to you.” To reduce classroom outbreaks, one of his children’s teachers “is meticulous about it,” he said, adding that she tells parents, “If your kid is sick, keep them home.”

“Everybody wants to tough it out and nobody wants to lose a sick day,” Dr. Baum said, but showing up for work when you are severely ill doesn’t do your employer any good, and puts your co-workers at risk.

Even divine power isn’t enough to keep people healthy at this time of year. At St. Teresa’s Catholic Church on Staten Island, parishioners were advised that during the flu season at masses they could replace the sign of peace, a handshake, with a simple wave, according to Rev. John O’Hara, who said he has been battling his own cold since before Christmas.

As far as remedies go, Dr. Roach said, “there is nothing that is great,” but some remedies might help to lessen symptoms. While vitamin C probably doesn’t work, Echinacea and zinc might ease symptoms, he said. And Dr. Roach said studies have proven that chicken soup really does help the body bounce back quicker.

On December 21, the city’s Department of Health and Mental Hygiene reported flu was “widespread” and that doctors can order additional flu vaccine for high-risk patients. At that point in the flu season the department said it had distributed more than 200,000 doses of flu vaccine.