Bloodstream infections may increase risk for MRSA mortality

April 2008

ATLANTA — Patients with bloodstream infections caused by invasive methicillin-resistant Staphylococcus aureus were nearly four times more likely to die from infection after 180 days than patients who had other types of MRSA infections, according to study results presented at the International Conference on Emerging Infectious Diseases, held here in March.

After only 30 days, patients with bloodstream infections caused by MRSA were at an increased mortality risk, according to data from the Active Bacterial Core surveillance component of the Emerging Infections Program in Davidson County, Tennessee. This state had the second highest incidence of invasive MRSA infection of nine sites included in 2005 surveillance data from a national emerging infections program, according to study researchers.

Case-fatality ratio

The researchers from the Tennessee Department of Health used vital statistics from Davidson County, Tennessee, from October 2004 to July 2007 to determine 30-day crude case-fatality ratio and mortality rates. Patient data from October 2004 to April 2007 were used to determine rates at 180 days.

The researchers reviewed state vital statistic data and matched patients by name and birth date to determine patient outcomes. For each matched case, researchers calculated the number of days from the date of an initial positive MRSA culture to the date of death on death certificates. This method was used to determine the numerator for 30-day and 180-day case mortality rates.

The researchers assessed 30-day and 180-day crude case-fatality ratio and mortality rates from invasive MRSA and analyzed factors associated with death.

“We wanted to see what would happen if we removed the in-hospital cases to find out what happened to patients after they left the hospital,” Kimberly R. Glenn, MPH, an epidemiology fellow at the Tennessee Department of Health, told Infectious Disease News.

Bloodstream infections accounted for 85% of all invasive MRSA cases during the study period, according to Glenn. “That is a huge population that we need to look at to assess risk,” Glenn said.

Comorbidities, including diabetes and HIV, and increased age also were associated with greater fatality from invasive MRSA. “With each additional comorbidity, we found that risk for death increased 20%,” Glenn said. “Strict adherence control measures will help prevent these deaths.”

Invasive MRSA rates in this study population were 59.1 per 100,000 between 2004 and 2007. Bloodstream infections were attributed to 85% of invasive MRSA cases. Patients with bloodstream infections had higher crude case fatality rates (14.7%) than patients with non-bloodstream infections (4.5%) at 30 days. At 180 days, case fatality rates were 21.4% among patients with MRSA bloodstream infections compared with 5.7% among patients with non-bloodstream infections.

Fatality rates at both 30-days and 180-days were higher among patients with health care-associated invasive MRSA than patients with community-associated MRSA.

The overall 30-day mortality rates from invasive MRSA were 13.2% and the overall 180-day rate was 19.1%. The 30-day mortality rate was 7.3 per 100,000 and the 180-day mortality rate was 9.9 per 100,000.

For more information:

• Glenn KR, Craig A, Kainer MA. Thirty-day and 180-day case fatality rates among invasive methicillin-resistant Staphylococcus aureus patients (Tennessee, 2004-2007). #540. Presented at: The International Conference on Emerging Infectious Diseases 2008; March 16-19, 2008; Atlanta.