Jan. 14, 2013 -- Little Cassie Colice fought off another coughing fit as she sat in the emergency room at Boston Children's Hospital with her mother. Despite getting a flu shot this season, doctors believed the toddler was suffering from the flu.
"She's gone from having what you think for a toddler is a common cold to having difficulty breathing, coughing up a lot of mucus, terribly lethargic, no appetite," said Cassie's mother, Meghan Moriarty. "It just makes me feel bad that she can't tell me."
"Nightline" spent the last 48 hours documenting a city in crisis from a raging flu epidemic, from patients who already have it to those who are taking measures to avoid it and the doctors who are battling the outbreak.
Moriarty was very concerned because Cassie, who isn't even 2 years old yet, was born prematurely, putting her in the highest risk category for serious complications from the flu. So doctors didn't waste time testing Cassie for flu. They admitted her immediately.
"She has a fever and cough, she's dehydrated, the degree of lethargy, the repertory rate makes me worry that she has a serious infection," said Dr. Anne Stack.
Once admitted, Cassie and her mother realized they had lots of company.
"We are at full capacity," Stack said. "The hospital is essentially completely full."
And it was not just Children's Hospital, all of Boston's world-famous hospitals are operating on overdrive. There have been more than 750 confirmed flu cases so far this season in Boston, more than 10 times the 70 cases from this time last year.
"I have been here for 19 years," said Dr. Ron Walls of Brigham and Women's Hospital. "I don't remember seeing anything like this."
At Massachusetts General Hospital, patient Shane Wells feared his laundry list of flu-like symptoms was making him another one of Boston's latest statistics. Despite getting the flu shot, the 41-year-old was suffering from chills, sweats and incessant cough.
"The aches and pains, the hot, the cold," he said. "[I'm] trying to get back to work because if you don't work you can't pay the bills."
Many people assume they have the flu without getting tested. But when Wells' lab tests came back, the results were positive for flu. There was little doctors could do for him. He had passed the 48-hour window when prescription medication could effectively treat the virus.
"You ought to be wearing a mask when you are in public," Dr. Stuart Harris told Wells. "Try to keep away from people, wash your hands all the time."
Back at Children's Hospital, Cassie's chest X-ray showed her lungs were full of mucus. She was also dehydrated and had low oxygen levels in her blood, so doctors admitted her to stay at the hospital overnight.
Just down the hall from Cassie was 4-month-old Cayson Page, who was born with congenital heart disease. For children like Cayson, the flu can be a matter of life or death.
"Our main concern is that this child doesn't have a lot of reserve," Dr. Stack said. "So even a little bit of illness can tip someone like this over."
Cayson was discharged from the hospital, but after repeatedly vomiting, his parents, James Page and Elizabeth Graul, brought him back to the ER. It was an exhausting and scary process and the Pages feared their son would become another Boston statistic.
"The main thing that worries me is just how many deaths have happened from [the flu]," Graul said. "With his heart disease, he gets really sick just off a simple cold and then I don't even want to know what the flu would do to him."
At Brigham and Women's Hospital, a code amber alert sounded.
"It is basically a disaster notification that we use when we have a large number of things to deal with," Dr. Walls said. "It freezes the staff so basically no one is going to be allowed to go home."
In one afternoon, Walls' section of the ER saw eight patients, more than four times what they typically see this time of year.
"The big difference I think that I've seen this year is that there is so many more people with it," Walls said. "So we talk about the virulence of the flu, like how fast can it get from me to you and from you to someone else. This flu seems to have spread from really rapidly through large, large numbers of people."
One of his biggest concerns was elderly patients, who are also at high risk of complications from the flu. Eighteen people over age 65 have already died from the flu in Massachusetts.
Many doctors still agree that the best weapon of defense against the flu is to get a flu shot. An East Boston neighborhood health center said they have given 20,000 flu shots this season and more than 700 alone on Saturday.
"We don't usually have to do big clinics like this but when there's a need, particularly like this when the flu is so severe, we really want to vaccinate people, we're happy to do this," said Dr. Catherine Silva, a local primary care physician.
Concerned parent Tequila Cunningham, who was waiting for her flu shot at the health center, said she wasn't taking any chances.
"There has been four episodes of kids getting sick in their school," she said. "I feel like the flu shot and some vitamin C and they're going to be great."
On Sunday, Cassie was still at Children's Hospital and had been moved into intensive care. She had to have mucus drained from her lungs but was slowly starting to improve.
"I think we might be able to get her home soon," Meghan Moriarty said.
But the ordeal has taken its toll and Cassie's mother was exhausted.
"I actually fainted last night," she said. "I forgot to feed myself."
But after 24 hours, Mass General patient Shane Wells, who felt awful after being discharged, said he was starting to feel a lot better
"I pretty much feel 80 percent," he said. "I'll make it back to work tomorrow, I'm feeling good now. I'll get a good night's sleep, keep taking my medicine and I think I'll be all right."
Boston-area hospitals reported a decline in flu admissions over the weekend, suggesting things are looking up in a city that is sick of being sick.