June 1 (HealthDay News) -- Elderly intensive care unit patients have less risk of infection if the units have high nurse staffing levels, says a Columbia University School of Nursing study.

Hospital-acquired infections are the sixth leading cause of death in the United States.

In this study, researchers reviewed outcomes for more than 15,000 patients in 51 hospital intensive care units (ICUs) across the United States. They found lower rates of infection in ICUs with high nurse staffing levels. The average staffing level was 17 registered nurse hours per patient per day.

The study also found that higher levels of ICU nurse overtime were associated with increased rates of infections and skin ulcers. On average, ICU nurses worked overtime 5.6 percent of the time.

The findings, published in the June issue of the journal Medical Care, support the idea that improving nurses' working conditions will boost patient safety, the study authors said.

"Nurses are the hospital's safety officers. However, nursing units that are understaffed and that have overworked nurses are shown to have poor patient outcomes," first author Patricia W. Stone, assistant professor of nursing, said in a prepared statement.