Flu is a major contributor, though, to what's going on.
"I'd say 75 percent," said Dr. Dan Surdam, head of the emergency department at Cheyenne Regional Medical Center, Wyoming's largest hospital. The 17-bed ER saw its busiest day ever last week, with 166 visitors.
The early onslaught has resulted in a spike in hospitalizations, prompting hospitals to take steps to deal with the influx and protect other patients from getting sick, including restricting visits from children, requiring family members to wear masks, and banning anyone with flu symptoms from maternity wards.
One hospital in Allentown, Pa., this week set up a tent for a steady stream of patients with flu symptoms.
But so far, "what we're seeing is a typical flu season," said Terry Burger, director of infection control and prevention for the hospital, Lehigh Valley Hospital-Cedar Crest.
On Wednesday, Boston declared a public health emergency, and all the flu activity has caused some to question whether this year's flu shot is working.
There's a new flu vaccine each year, based on the best guess of what flu viruses will be strongest that year. This year's vaccine is well-matched to what's going around. The government estimates that between a third and a half of Americans have gotten the vaccine.
But the vaccine isn't foolproof, and even those who were vaccinated can still get sick. At best, the vaccine may be only 75 percent effective in younger people and even less so in the elderly and people with weak immune systems.
Health officials are analyzing the vaccine's effectiveness, but early indications are that about 60 percent of all vaccinated people have been protected from the flu. That's in line with how effective flu vaccines have been in other years.