Updated

If you had to guess the condition linked to half of all hospital deaths, what would you say? Heart attack? Cancer?

The answer, according to new research published in the Journal of the American Medical Association, is sepsis. The condition was present in 35 to 52 percent of inpatients who died in more than 1,000 U.S. hospitals in 2010, the study finds.

Sepsis kills more than one in four people who suffer from it, according to the National Institutes of Health. Anyone can get it, but children and the elderly are most vulnerable. (From medication mix-ups to dirty hands, we found the 8 Secrets Your Hospital Keeps.)

What is it? Sepsis can happen when your body overreacts to infection, said Dr. Colin Cooke, a critical care physician and health services researcher at the University of Michigan. “The body's defense turns on itself, which can lead to organ failure and potentially death,” he said.

The most common causes are pneumonia, urinary tract infections, abdominal infections like appendicitis, and skin and soft-tissue infections, Cooke said. Sepsis can begin with something as simple as a bad scrape.

While that sounds terrifying, you don’t have to panic every time you get a gash on your knee. A very small percentage of those cases actually lead to sepsis, Cooke said. (Antibiotics that were once considered last-resort medicines are failing. Learn How You're Helping to Create the Next Killer Disease and protect yourself.)

It’s when your small gash becomes extremely painful, red, and angry-looking--and you’ve got a fever or night sweats, to boot--that you should see your doctor immediately, Cooke urged.

Since catching sepsis early is key, you should also call your doc if you have either of these symptoms:  
• A burning sensation when you urinate
• Coughing up mucus
• Combined with these symptoms:
• Fever, lightheadedness, shortness of breath, grogginess, poor urine output, or extreme concentration in urine

Are you neglecting the unwritten rules of hygiene? You might not even realize it, but here are the Super-Gross Things You Do Without Thinking About It.)