Federal health officials declared this season's flu outbreak an epidemic Friday as Maryland hospitals and clinics continued to treat unusually high numbers of patients for the virus and manufacturers reported low supplies of the vaccine to treat the illness.
The Centers for Disease Control said the virus is widespread in Maryland and 46 other states — the worst flu season in a decade. More than 15,000 Marylanders have visited emergency rooms and doctors' offices with flu-like symptoms this season, according to numbers updated Friday by the state Department of Health and Mental Hygiene.
The outbreak has killed 20, all of them children, across the country so far, compared to 34 last flu season. No deaths have been reported in Maryland.
Other viruses similar to flu are spreading this year, landing people in the hospital and home sick in bed.
While the epidemic is showing signs of slowing down in some parts of the country, health officials said they don't know when it will peak because the flu is so unpredictable. Some hospitals have stopped testing people for the virus because of the numbers of patients.
"We're seeing a lot of people. We have been very busy," said Dr. Stephen Schenkel, chief of emergency medicine at Baltimore's Mercy Medical Center, where doctors have stopped testing for the disease.
There is not much doctors can do to treat the flu, which eventually dissipates on its own. Anti-virals are given to high-risk patients.
The CDC also released Friday its first report on the effectiveness of this year's vaccine, which the agency said is working in 62 percent of people who get the shot. Each year drug manufacturers create a vaccine using forecasts of which strain of flu is expected to infect people.
Health officials said the vaccine is still the best way to beat the flu and encouraged people to get the shot if they haven't already.
"The flu shot is still our first line of defense, and people still have time to get one," said Linda Josephson, head of infectious disease prevention and management at the Anne Arundel County Department of Health.
The severity of this year's outbreak, which also hit earlier than is typical, follows several mild influenza seasons. The principal strain infecting people is one generally associated with more severe symptoms, such as diarrhea and nausea.
No one knows precisely why this season is so much worse. Some people may have strains of the virus that the current vaccine doesn't protect against. Most of the people who have become sick didn't get vaccinated, according to doctors and health officials.
The flu season typically runs from late September through late May and peaks in January and February, meaning people could continue to get sick for several more weeks.
About 37 percent of Americans, or 112 million people, received the flu vaccine through the middle of November, the CDC said.
The University of Maryland Medical Center has already treated more patients than it did all of last season. The Baltimore medical center reported 60 influenza cases since September, compared to 32 total flu cases all of last season.
Johns Hopkins Health System officials said that although the flu season started earlier than usual, they believe the season is otherwise on track to be a relatively normal year.
Other areas have seen spikes. In Anne Arundel County, 3 percent of emergency room visits this week were for people with flu symptoms, a number higher than most years, Josephson said. She said that some grocery stores and pharmacies in the county were running low on the vaccine, although most Baltimore-area hospitals said they still have adequate supplies.
Drug manufacturers produced 135 million doses of the vaccine this year, and 128 million have been distributed to health care providers. The CDC said there should be enough to treat people, but the drug may be hard to find.
Pharmacies at Giant Food, the region's largest grocer, were experiencing a shortage of flu vaccine because of "significant demand," said spokesman Jamie Miller. "We have ordered additional vaccine and expect to replenish all of our pharmacies by early next week," Miller said.
A spokesman for Safeway said some of its pharmacies have had to reorder vaccine because of a spike in customer demand in the past few days. "If they run out one day, they'll have more within the next day or so," said the spokesman Greg TenEyck.