Study estimates Staphylococcus aureus infections cause 12,000 deaths, cost hospitals $9.5 billion

Staphylococcus aureus infections (S. aureus) create an enormous burden to hospitals by significantly increasing costs, length of patient stays and mortality rates, a Northwestern Memorial Hospital researcher found in the most comprehensive study to date, published today's Archives of Internal Medicine.

The study, led by Gary Noskin, MD, an infectious diseases specialist and medical director of healthcare epidemiology and quality at Northwestern Memorial, examined two years of data from hundreds of hospitals.

"S. aureus infections represent a considerable burden to U.S. hospitals, particularly among high-risk patient populations," said Dr. Noskin. "The potential benefits to hospitals in terms of reduced use of resources and costs, as well as improved outcomes from preventing S. aureus infections, are significant."

"There are currently a number of things being done to reduce the number of hospital-acquired S. aureus infections, including use of antibiotics to prevent surgical site infections, consistent hand-washing and maximum barrier protections when putting in central lines," adds Dr. Noskin. "There are also strategies to reduce S. aureus infections that are brought into the hospital such as performing a nasal swab to screen for S. aureus then attempting to eliminate it. Another important intervention is to make sure patients with certain infections are placed in isolation."

S. aureus infection was listed as a discharge diagnosis in nearly 1 percent of all hospital stays, or an average of 292,045 stays in a year, the study found. And S. aureus infection stays had, on average, 3 times the length of stay (14.3 vs. 4.5 days), three times the total charges ($48,824 vs. $14,141), and five times the risk of in-hospital death (11.2 percent vs. 2.3 percent) than stays without this infection. Even when controlling for patient differences in age, gender, race and comorbidities, the differences were significant: 9.1 days in excess length of stay, $32,856 in excess charges and 4 percent in-hospital mortality.

Applying these per stay estimates to the total number of S. aureus stays in the United States in a given year results in an estimated 2.7 million days in excess length of stay, $9.5 billion in excess charges, and close to 12,000 inpatient deaths per year. The differences remained significant when also comparing hospitalizations with S. aureus infections with other types of infections.

The study did not distinguish between infections that occurred before admission to the hospital or during a hospital stay. Also, the inability to measure "out of hospital" mortality, or mortality subsequent to the hospital stay, likely underestimates the impact of S. aureus infections on mortality.

S. aureus is a bacterium, frequently living on the skin or in the nose of a healthy person that can cause illnesses ranging from minor skin infections and abscesses, to life-threatening diseases. Long recognized as a frequent cause of healthcare-associated infections in acute care hospitals, it is often responsible for hospital-acquired pneumonia and surgical site infections, and is the second most common cause of bloodstream infections. An increasing percentage of S. aureus infections are caused by antibiotic resistant strains of the organism.

3M Healthcare was a study sponsor and financial support also came from a grant from the U.S. Public Health Service. According to Edwin Hedblom, health economic business manager from 3M Health Care, "no prior study has estimated the impact of S. aureus infections to this degree, in terms of clinical and financial outcomes that include length of stay (LOS), total charges, and in-hospital mortality, from nationally representative data."

Patient discharge data from 994 hospitals in 28 states in 2000 and 986 hospitals in 33 states in 2001 -- representing approximately 14 millions inpatient stays -- was analyzed to determine the association of S. aureus infections with length of stay, total charges and in-hospital mortality.

Other findings include:

• Patients undergoing an orthopedic, cardiovascular, and neurosurgical procedure that have S. aureus infection spent 16.6 additional days in the hospital and at a cost of $68,944 as compared to patients without S. aureus infections.
• Patients undergoing an orthopedic, cardiovascular or neurosurgical procedure with S. aureus infections had a nearly five-fold risk of in-hospital death compared to patients without this infection. The differential in absolute risk of mortality was greatest for cardiovascular procedures.

• Among the hospitalizations analyzed, S. aureus infections were most likely to occur in neurosurgery stays (1.4 percent) and least likely to occur in orthopedic surgery stays (0.3 percent).