The number of flu outbreaks at nursing homes, hospitals, and other healthcare facilities in the five boroughs is nearly twice what it was at this time last year, and health officials have detected a rise in flu cases in the city in the past week, the Health Department announced yesterday.

After a rocky start to the flu season marked by a major national shortage of flu vaccine, the city Department of Health and Mental Hygiene said yesterday that 21 facilities had reported outbreaks to date. The agency also reported more visits to emergency rooms in the past week, an increase in sales of over-the-counter cold medications at pharmacies, and a jump in appointments with doctors.

“Flu is now widespread in New York City,” the city’s health commissioner, Thomas Frieden, said in a statement. He went on to say the city still has enough vaccine to provide inoculations for those at high risk of getting gravely ill from the flu. That includes individuals over age 65, people with compromised immune systems stemming from chronic medical conditions such as diabetes or asthma, and children between the ages of 6 months and 23 months.

The agency is taking the unusual step of making vaccine available for private practice doctors to purchase until January 9, because many physicians did not receive adequate supplies this year when one of the two flu-vaccine manufacturers in Britain, which America relies on for shots, was unexpectedly shut down for reasons of quality control. The minimum order for physicians is 40 doses and the cost is approximately $8 per dose, according to the health department.

A spokeswoman for the department, Sandra Mullin, said it was too early to know whether the there was a connection between the widespread flu at this time of year and the shortage of vaccine. The agency distributed 200,000 vaccinations, but that does not account for shots administered at private hospitals and doctors’ offices. In all, Ms. Mullin said, more than 1 million doses were expected in the city.

“We do see an increase in flu activity around this time every year,” she said in a phone interview last night. “We are now urging anyone who is at risk of serious illness from the flu to step forward now and get a shot.”

She also stressed that it was impossible to know whether this would be a particularly acute season until the flu has run its course. It may simply be peaking early. Physicians at Staten Island University Hospital have seen an increase in the number of patients admitted with the flu in the past week, according to the vice president of medical operations, Theodore Strange. With concern about the season’s vaccine shortage, only health workers and the most susceptible patients – a combined 1,500 people – received vaccinations in December.

“Of course I’m worried. We should have immunized people three or four weeks ago,” Dr. Strange said when reached by phone last night.

He said, however, that he is confident more high-risk individuals will be inoculated now that the state and city have released more vaccine. “Over the next 30 to 40 days, we can immunize patients and minimize the effect of this flu outbreak,” he said.

A spokeswoman for Saint Vincent Catholic Medical Centers, Debbie Cohen, said the institutions have not seen an increase in the number of flu cases. Reports of a vaccine shortage have discouraged people from getting shots, she said.

“We’re seeing that people have kind of given up on getting vaccinated, when in fact right now we are able to vaccinate for the flu,” Ms. Cohen said. “Word needs to get out to the public that they need to get vaccinated now.”