For six hours in a Saint Luke's Hospital emergency room, Dakota Allen worried that he might become a fatal pneumonia statistic. He'd been coughing for weeks.

"I overlooked it," said the 20-year-old who works two jobs in Kansas City. "I thought it could be early flu.

It wasn't. Pneumonia had him firmly in its clutches. "You don't have to be asthmatic or elderly or a child for it to get as serious as it can get," he said.

About 1 million U.S. adults. are hospitalized with pneumonia every year, and 50,000 die from it, said the American Thoracic Society. Influenza and pneumonia often hit together, though there is no "pneumonia season."

"If you look at pneumonia by itself, yes, it is a more serious diagnosis than, say for example, run-of-the-mill flu or cold or anything like that, because lots more people get hospitalized with it, and a lot more people die from it," said Raghavendra Adiga, an infectious disease specialist. "Pneumonia is a big killer among infections that are out there and it's the second most common reason to be in the hospital."

Anyone can get pneumonia, a lung infection. Half of all U.S. adults with a healthy immune system who are hospitalized for severe pneumonia are between 18 and 57, the Thoracic Society said. "While young healthy adults have less risk of pneumonia than the age extremes, it is always a threat," it said.

People might not know they have pneumonia because the symptoms, the Mayo Clinic said, mimic symptoms of the flu or a cold, "but they last longer." Symptoms include chest pain when you breathe, a cough that hacks up phlegm, a fever and shortness of breath.

"The thing you want to watch out for is being short of breath. 'Am I getting short of breath not doing anything?' Then they need to have it checked out," Adiga said.

Just because you have a cough doesn't mean you have pneumonia. The only way to diagnose it "is with a good exam and of course getting a chest X-ray," he said.

It's rare that pneumonia gets better without treatment, he said. "Typically [people] will get sicker and sicker and seek help."

Other ways to avoid pneumonia? "Stay away from sick people," Adiga said.