Flu activity continues to be widespread in Massachusetts, public health officials said today in a weekly report drawn from the number of people visiting their doctors with fever, cough, and sore throats.

Patients are not routinely tested to see if they have swine flu, or H1N1, but because there are so many more cases than usual this early in the winter flu season, most illnesses are assumed to be caused by the H1N1 virus. About 5 percent of visits to doctors represent flu-like illnesses, the state said, well above peak levels in previous years.

A growing number of flu cases among patients has prompted Massachusetts General Hospital to change its policy for visitors. Last week the hospital barred children and teenagers from its obstetrics unit because children are both more likely to catch and transmit the flu.

As of Monday, children 18 and under are asked not to come to any part of the hospital unless they are patients, associate chief nurse Debra Burke said today. She also urged people with flu symptoms and anyone who has been around someone sick with the flu to stay away, again unless they are patients.

"Before you have symptoms of flu, you could have the flu and be shedding the virus for up to two days," she said. "We're just asking people to be really careful."

Alcohol advertising inside MBTA subway cars reaches thousands of Boston Public School students every school day, a new study from Boston University reports, exposing young people to the kind of messages that research links to increased underage drinking.

A team from the Boston University School of Public Health sampled about 30 percent of Boston's subway cars and found an average of almost two ads for alcohol per subway car on the Orange, Red, Green and Blue lines. The Orange Line had the most and the Red Line had the fewest alcohol ads.

They concluded that the ads -- mostly beer and bourbon -- were seen more than 18,000 times per day by students from 11 to 18 years old as they rode to and from school, reaching about half of the more than 9,000 students who travel to school by subway each day, according to ratings used by advertisers to measure the success of their ads. That level of reach is the same as those students seeing about five Super Bowl ads every day, study senior author Dr. Michael Siegel said in an interview.

State public health specialists are warning consumers that ground beef contaminated with E. coli bacteria may have been sold by four Massachusetts supermarkets, in a second, unrelated outbreak affecting the state in a week.

Shaws, Price Chopper, Trader Joe’s, and Wild Harvest may have sold fresh ground beef products distributed by Fairbank Farms, an Ashville, NY, meat distributor, Massachusetts health officials said today. The US Department of Agriculture has linked illnesses in Massachusetts, Connecticut, and Maine to ground beef contaminated with the same strain of E.coli:O157:H7. Each package had "EST. 492" inside the USDA inspection mark or on the nutrition label. For information on specific products at the four stores, go to the USDA site.

Today's news follows an unrelated E. coli outbreak last week in which more than 20 children and adults from Rhode Island became ill after eating ground beef at Camp Bournedale in Plymouth. South Shore Meats in Brockton recalled ground beef that had been distributed in institutional size packages.

Because raw meat can contain disease-causing bacteria, health specialists urge consumers to cook meat fully to a temperature of 160 degrees F, the level necessary to destroy disease-causing organisms such as E.coli, Campylobacter, and Salmonella.

E. coli can be deadly in the very young, the very old, and people with weakened immune systems. More information is available through the state Department of Public Health.

Budget cuts to public health programs in Massachusetts were not nearly as deep as some advocates had feared, but prevention programs will still suffer, a statewide group says.

Last month the Massachusetts Public Health Association warned that the state Department of Public Health would lose $32 million, or 9 percent of its non-hospital budget, to 9C budget cuts, named for the section of state law granting budget-cutting authority to the governor. But cuts made last week by Governor Patrick totaled $8 million. The spending changes are being made to help bring the state's budget into line with drastically lower revenues.

Some of the public health programs affected are smoking prevention and cessation services, teen pregnancy prevention programs, school health programs, and the sexual assault nurse examiner program.

"We are troubled that community-based prevention programs continue to be sacrificed," Valerie Bassett, executive director of the association, said in a statement. "These programs which prevent disease and injury in schools, community health centers, and out in the streets continue to be dismantled."

By Stephen Smith, Globe Staff

Massachusetts patients stricken with the chills, coughs, and fever that are the calling card of influenza are streaming into physician offices at a higher rate than any time during the past two flu seasons, state disease trackers reported today.

It is, said disease specialists and doctors on the front line, strong evidence that swine flu has the state in its cross hairs once again after subsiding in late summer.

The proof can be found in Davis Square, inside the waiting room of the Harvard Vanguard Medical Associates outpost.

"We're having people waiting much longer than we usually do, and we're having schedules that are overflowing, and having doctors and nurses staying longer than normal," said Dr. Benjamin Kruskal, who treats children in the Somerville clinic. "We're already starting to push the capacity of the system."

Emergency doctors at Children's Hospital Boston began seeing an increase in what they think are swine flu cases over the weekend, Dr. Anne Stack, clinical chief of emergency medicine, said yesterday.

About 25 to 30 children a day are coming to the hospital with the hallmarks of flu -- fever, cough, sore throat, congestion, and headaches -- pushing the total number of emergency patients 40 percent higher than usual for this time of year. Doctors are not testing patients for flu, but they see the uptick in visits as a sign of the spreading H1N1 virus.

"Normally this time in October we see 170 kids a day, but on Monday, we saw 240," Stack said. "We are assuming everything that looks like flu is probably H1N1."

Several hundred Harvard students are taking part in an experiment that tests social networks as early warning systems for disease spread, the Harvard Crimson reports.

Dr. Nicholas A. Christakis, who is a Harvard Medical School professor as well as a house master at Harvard, is well known for his research into social networks as important influences on behavior. His work has linked the spread of happiness, quitting smoking, and obesity to circles of friends.

Now he is asking 650 randomly selected Harvard undergraduates to report twice a week for 12 weeks on whether they have flu symptoms, the story said. The students are also being asked to supply the names of three friends and to assess their own popularity.

"By looking both at whether you’ve had the flu and where you are in the social network, we think you can get an early warning of an epidemic," Christakis told the Crimson. "If this works, we’ll have invented a new method for attacking diseases, which could have broad relevance far outside Harvard."

By Stephen Smith, Globe Staff

A wave of gastrointestinal illness at a Plymouth camp has been linked to bacteria-tainted ground beef, forcing the supplier of the meat to institute a recall, state public health authorities said tonight.

More than 20 schoolchildren and adults from Rhode Island became ill after visiting Camp Bournedale the week of Oct. 13, the Massachusetts Department of Public Health said. No deaths or life-threatening illnesses have resulted from the infections, a state health spokeswoman said.

Tests of ground beef obtained from the nature camp showed that the meat carried a dangerous strain of E. coli that has caused deaths in other outbreaks. The exact same O157:H7 strain of the bacterium was present in two ill children who were tested.

South Shore Meats Company of Brockton voluntarily recalled certain ground beef and other beef products, according to an announcement from the state health agency. Company officials could not be immediately reached for comment.

Flu activity is widespread in Massachusetts for the first time this fall, public health officials said today, leading a Central Massachusetts high school to close its doors until Wednesday and almost certainly reflecting cases caused by the swine flu virus, whose return has been expected since it first emerged in the spring.

This week's bump in flu-like illnesses monitored by the state Department of Public Health makes the state one of 46 in the country to with widespread flu activity, according to the US Centers for Disease Control and Prevention.

"We had always been predicting this," Dr. Lauren Smith, the state's medical director, said today. "We knew the H1N1 virus was going to be increasing. We didn't know when, but now we do. It's here."

Grafton High School closed early today after more than a third of its students and more than a quarter of its staff stayed home sick. It is the only school in the state to close, according to public health and education departments, but absenteeism has been elevated some communities across the state. At the beginning of the school year, state officials urged schools to close only as a last resort during flu season and instead focus on keeping sick students isolated at home. Grafton school and public health officials were in close contact with the state health department before today's action, Smith said.

Over the past few days there was an uptick statewide in the proportion of people going to their doctors with flu symptoms, Smith said. But the levels are half as high as during the H1N1 outbreak in the spring and a third as high as seasonal flu's peak last winter.

"This is very early for seasonal flu," Smith said. "We can safely assume that flu activity this early in October is probably due to H1N1."

Some hospitals in the state are limiting who can visit their patients, the Associated Press reported today. Children 13 or younger will not be allowed to visit patients at the UMass Memorial Medical Center hospital's three Worcester campuses. The policy applies to all young children healthy or not, but anyone showing possible flu symptoms will be prevented from visiting patients.

Southcoast Hospitals Group is barring anyone under the age of 18 from visiting patients in the pediatric and maternity wards at its hospitals in New Bedford, Fall River and Wareham.

By Michaela Stanelun and Elizabeth Cooney, Globe Correspondents

Grafton High School will be let out early today and remain closed on Monday and Tuesday after a high number of students and faculty came down with suspected cases of swine flu.

Superintendent Dr. Joseph F. Connors said that this week brought "five days of escalating absenteeism for staff, faculty, and students."

"We wanted to keep the building open as long as we could run a productive and safe school," Connors said.

Grafton is one of several school districts to contact the state Department of Public Health this week with concerns about high absenteeism rates, spokeswoman Jennifer Manley said this morning. The department offers advice but does not direct schools to close, consistent with guidance from the US Centers for Disease Control and Prevention issued in the summer.

Before the school year began, Massachusetts health authorities recommended that schools close only as a last resort during flu season and instead focus on keeping sick students isolated at home. Grafton school and public health officials were in close contact with the state health department before today's action, Manley said.

"It is a decision that is made locally," she said.

At the state Department of Elementary and Secondary Education, a spokesman said he was aware of only Grafton's decision to close.

"We are absolutely monitoring it" across the state, J.C. Considine said. "It's really a decision that needs to be made locally between the local school district and the local board of health."