Trish M. Perl, a professor of medicine and pathology at Johns Hopkins Medicine, said the major hospitals in Baltimore have treated more than a dozen patients for the flu in the past week, up from a handful of cases since flu season officially began in the U.S.
"There's a lot of data now suggesting that flu is hitting in this area," Perl said. "I think that's kind of the nature of flu. You kind of get dribs and drabs and then all of a sudden you see a huge increase."
The majority of flu cases in Maryland and in the U.S. as a whole have been influenza A, a collection of common strains that include H1N1, also known as swine flu, according to the CDC. Those strains are covered by this year's flu vaccine.
Nearly two dozen people were hospitalized for the flu across the state, with more than 400 people testing positive for the flu in state and clinical labs for the week that ended Dec. 28, according to data collected by the state Department of Health and Mental Hygiene and given to the CDC. The CDC did have not have a detailed geographic breakdown of cases.
Nationally, flu cases are also on the rise, and the virus has been deadly in some Western states. Doctors said people, especially high-risk populations such as seniors, children and those with compromised immune systems, should get their vaccinations now and practice preventive measures such as hand washing and avoiding people who are coughing and sneezing openly.
"This is a bad disease, and I think people have a real underappreciation that this kills people," Perl said. "We're on the upswing and, of course, with all the kids going back to school, that's going to fuel the fire."
On Saturday, Erika Carroll, a clinical care specialist at the MedStar PromptCare center in Pikesville, jabbed a needle into the left deltoid of David Almond, 38. The Owings Mills resident was one of several dozen people who have sought a flu shot at the clinic this season.
Almond said he wanted to keep himself healthy, especially because he'll be around his girlfriend's 1-month-old grandson.
"I've had walking pneumonia a few times," he said after Carroll affixed a bandage to his arm. "I just don't want to get too sick."
Kenneth Veenema, a doctor who works at MedStar's urgent-care clinics, including the one in Pikesville, said he's also noticed an uptick in cases recently, including seven new cases the other day at a clinic in Wheaton. Only one person has tested positive for flu so far at the Pikesville clinic, which opened in July.
As of last week, the CDC classified Maryland's flu outbreak as "regional," a step below "widespread." Flu is widespread in Virginia, Pennsylvania and many other states, and Veenema said that could increase chances of a larger outbreak in Maryland.
"We're really just starting to see it," Veenema said. "I can imagine that in a couple of weeks we could be widespread here, but it's hard to predict."
So far, no one has died of the flu in Maryland this season, according to the CDC.
"The types of flu we've been seeing so far have been mild," Veenema said. "So far, so good."