Pneumonia and blood-borne infections caught in hospitals killed 48,000 patients and cost $8.1 billion in 2006, according to a report released on Monday.

The study is one of the first to put a price tag on the widespread problem, which is worsening and which some experts say is adding to the growing cost of healthcare in the United States.

"In many cases, these conditions could have been avoided with better infection control in hospitals," said Ramanan Laxminarayan of Resources for the Future, a think tank that sponsored the study.

Sepsis — a blood infection — killed 20 percent of patients who developed it after surgery, Laxminarayan and colleagues reported in the Archives of Internal Medicine.

They studied hospital discharge records from 69 million patients at hospitals in 40 U.S. states between 1998 and 2006, looking for two diagnoses — hospital-acquired pneumonia and sepsis.

Patients who developed sepsis after surgery had to stay in the hospital on average nearly 11 days extra, at a cost of $32,900 per patient, they found. And just under 20 percent of them died.

Pneumonia patients stayed an extra 14 days after surgery, at a cost of $46,400 and more than 11 percent of them died, the researchers found.

"That's the tragedy of such cases," said Anup Malani of the University of Chicago, who worked on the study.

"In some cases, relatively healthy people check into the hospital for routine surgery. They develop sepsis because of a lapse in infection control and they can die."

The researchers said that 1.7 million healthcare-associated infections are diagnosed every year.

Many are due to drug-resistant bacteria, such as methicillin resistant Staphylococcus aureus or MRSA, which cost more to treat because only a few drugs can work against them. These infections can also be caught outside hospitals and some studies show that such community-acquired infections are also on the rise.

One estimate from Pfizer Inc suggested that treating MRSA alone cost $4 billion a year.

Measures to prevent infection are simple and include careful hand-washing, hygiene and screening patients when they check in. However, these measures are difficult to enforce, many studies have found.