Professional liability claims against hospitals are becoming more common and more severe after years of relatively infrequent losses, a new report says.

According to the 10th annual Hospital Professional Liability and Physician Liability Benchmark Analysis, the number of hospital professional liability claims is increasing and is expected to increase by 1% per year.

The study, released by Aon Corp. and the American Society for Healthcare Risk Management, both based in Chicago, polled more than 1,500 facilities to examine trends in claims and loss costs related to hospital and physician professional liability.

The study attributes the rise in claims to the economic downturn, less public sympathy toward health care providers, and a 2008 rule that prevents the Baltimore-based Centers for Medicare and Medicaid Services from reimbursing hospitals for certain errors known as “never events” because they are considered preventable and should never happen.

“Worsening economic conditions in 2008 may have influenced individuals to assert claims against hospital systems,” Erik Johnson, health care practice leader for Aon’s Actuarial and Analytics Practice and author of the analysis, said in a statement.

The frequency of hospital liability claims had been decreasing for about a decade before this year, the study said. Claims severity, which includes indemnity and defense costs, is now projected to increase 4% per year. Hospital loss costs per occupied bed, which is a major part of the total cost of risk, is anticipated to rise 5% in 2010, according to the study.

One-quarter of all claims and about 24% of hospitals’ professional liability costs are connected to hospital-acquired conditions such as infections, medication errors, objects left in the body after surgery and pressure ulcers, the study said.

The market for health care industry professional liability coverage likely will remain stable for the rest of the year, but pricing is expected to increase in 2010, Aon said.