"So the choice of codes has tremendous implications for hospital payment," added Lindenauer.
Using a large, national hospital database, the researchers also evaluated changes in hospitalization and death rates in patients who had conditions they thought might be less susceptible to changes in coding.
The investigators found that from 2003 to 2009, the hospitalization rate of patients with a principal diagnosis of pneumonia decreased from 5.5 to 4.0 per 1,000 patients, a drop of 27 percent. And pneumonia deaths declined from about 6 percent in 2003 to about 4 percent in 2009.
Over the same time period, the hospitalization rate for patients with a principal diagnosis of sepsis and a secondary diagnosis of pneumonia increased 178 percent, from 0.4 to 1.1 per 1,000 patients.
"What we came to hypothesize was that a shift was taking place whereby patients who'd previously been the sickest pneumonia patients were increasingly being coded as having sepsis," said Lindenauer.
He said hospitals get reimbursed more for patients with sepsis, so there's a strong financial incentive for coding based on sepsis versus pneumonia.
During the same time period, a national campaign was launched to raise awareness about sepsis and its treatment among physicians, which may also have influenced coding.
"There was probably a double-whammy of increased reimbursement and also an increase in physician awareness, so more were writing it in the chart and that allowed more hospitals to get reimbursed," said Lindenauer.
The researchers looked at the data in another way, too. They combined patients with sepsis, pneumonia and respiratory failure, and analyzed results. While they found hospitalizations were still declining for this combined group, the figures didn't drop nearly as much as when the pneumo
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