They are the young. The hip. And the sick.
This season's parade of coughing, wheezing and achy flu patients has a younger spin to it, caused by the re-emergence of the H1N1 strain of the flu virus and this year's relatively effective flu vaccine.
"Typically, you think it will be the really old or the really young," said Marc Itskowitz, an associate professor of medicine and internal medicine physician at Allegheny General Hospital. "This year, the cluster is really in young adults."
Through Saturday, there were 209 confirmed flu cases in Allegheny County this season, with 93 of those coming in the week that ended Jan. 11. Of those 209 cases, 100 people were hospitalized for treatment, said Guillermo Cole, spokesman for the county health department.
More than 90 percent of the flu cases statewide have been identified as the H1N1 strain, known as "swine flu" in 2009 when it re-emerged after lying dormant since the 1960s and 1970s. Because younger people haven't had much previous exposure to H1N1, their immune systems are more vulnerable than those who encountered it half a decade ago.
Unlike in 2009, this season's flu vaccine does cover H1N1, meaning that those who are vaccinated have some protection against it.
But that leaves young adults, many of whom did not get vaccinated, disproportionately vulnerable.
"The overall population gets vaccinated at a rate of 35 to 40 percent," Dr. Itskowitz said. "It's much less in generally healthy young adults."
The majority of the flu patients at Allegheny General have not been vaccinated, he said. With the flu season often stretching until April or later, he urged those who have not yet been vaccinated to do so as soon as possible.
Countywide, the age of flu patients has been somewhat higher. The average age for the 209 confirmed cases was 47, said Mr. Cole. At this point last year, when the flu season started unusually early, there were 488 confirmed cases in Allegheny County with an average age of 51.
The county health department reports two confirmed deaths from the flu this season: a 53-year-old woman and a 62-year-old woman. More deaths might be confirmed in coming reports; Dr. Itskowitz said he believed there have been four flu deaths at Allegheny General.
And the overall impact of the flu is much more widespread. For every one person with an officially diagnosed case of the flu, there might be 100 to 1,000 more people who have the flu and do not get their diagnosis confirmed, said Dr. Itskowitz.
A run-of-the-mill case of the flu generally does not require medical attention, said Donald Yealy, chair of the department of emergency medicine at UPMC.
"Most people don't need to be seen in a hospital emergency department," he said. "When you take yourself or your loved ones around, you run the risk of spreading whatever you were fearful of or picking it up. And if you didn't have it, you might end up getting it there."
Dr. Yealy recommended seeking emergency medical treatment for patients with severe symptoms, such as difficulty breathing, dizziness because of an inability to take in fluids and the worsening of other chronic conditions. Those in doubt can always call their primary care physicians, he said.
About 6 percent of patients being seen in county emergency rooms are there because of influenza symptoms, said Mr. Cole, compared to a 2 percent baseline in nonflu season.
"This is typical, maybe even typical plus a bit more, but not nearly the intensity as in 2009," Dr. Yealy said.
In addition to getting a flu shot, the best prevention comes from simple hygiene measures such as covering up coughs and hand-washing. "Everything you need to know, you learned in kindergarten," he said.
Figures from the Pennsylvania Department of Health, which include confirmed and suspected flu cases, put Allegheny County at 520 cases, Butler at 219, Westmoreland at 276, Washington at 202 and Beaver at 166.
Based on state figures, the flu virus seems to be affecting Western Pennsylvania more than elsewhere. The only other county statewide that has more than 200 cases is Blair County, with 381 reported.
National figures from the U.S. Centers for Disease Control and Prevention rate Pennsylvania's flu activity as moderate, noting that states can have pockets of high or low intensity.
Based on the rapid recent escalation of flu cases, Dr. Itskowitz believes that flu season may be nearing its height.
"I suspect we're approaching the peak," he said, "although you never know for sure."
Anya Sostek: email@example.com or 412-263-1308.