Laird Harrison

January 15, 2014

SAN FRANCISCO — For patients undergoing major surgery, being black, American Indian, older, uninsured, or receiving treatment in a smaller hospital increases the risk for methicillin-resistant Staphylococcus aureus (MRSA) infection, compared with other demographic groups, a new study shows.

And when patients from these groups are infected with MRSA, they have worse outcomes, noted researcher Veerajalandhar Allareddy, MD, clinical assistant professor of pediatrics at Case Western Reserve University in Cleveland.

"Hospitalized patients who underwent a major surgical procedure and developed an MRSA infection had a higher risk of mortality and increased hospital resource utilization," Dr. Allareddy reported.

He presented the study results here at the Society of Critical Care Medicine 43rd Critical Care Congress.

More and more people are undergoing major surgery, and multidrug-resistant organisms are infecting many of them. But just how many is not clear, Dr. Allareddy said.

To determine the rate of hospital-acquired MRSA infection, Dr. Allareddy and his team retrospectively analyzed the Nationwide Inpatient Sample database for 2009 and 2010. They found 22,932,947 hospitalizations involving a major surgical procedure and 235,636 MRSA infections, for a rate of 1.03%.

The 10,839 patients they judged to have had a history of MRSA or to have been a carrier of the bacteria were excluded from the analysis.

Of the hospitalizations analyzed, surgical-site infection accounted for 0.84% of cases, septicemia accounted for 0.09% of cases, and pneumonia accounted for 0.10% of cases.

Table. Odds Ratios for MRSA Infection

Variable Odds Ratio 95% Confidence Interval P Value
   Female 0.68 0.66–0.70 <.001
   Male reference  
Primary payer      
   Medicare 0.63 0.59–0.68 <.001
   Medicaid 0.71 0.67–0.76 <.001
   Private insurance 0.47 0.44–0.50 <.001
   Other insurance 0.75 0.69–0.82 <.001
   No insurance reference  
   Asian, Pacific Islander 0.58 0.52–0.65 <.001
   Black 1.19 1.13–1.24 <.001
   Hispanic 0.85 0.79–0.91 <.001
   Native American 1.27 1.01–1.60 .04
   Other 0.84 0.76–0.92 <.001
   White reference  
Each 1-year increase in age 1.0034 1.0023–1.0045 <.001
Each additional comorbid condition 1.38 1.36–1.39 <.001


Of the regions in the United States, patients in the Northeast had the lowest risk for MRSA infection, followed by the Midwest, the West, and the South.

In addition, patients treated in large hospitals were at lower risk for MRSA infection than those treated in small and medium-sized hospitals (odds ratio [OR], 0.87; P < .001). And patients treated in teaching hospitals were at lower risk than those treated in nonteaching hospitals (OR, 0.94; P < .001).

Factors associated with dying in the hospital were similar, except black patients had a slightly higher risk than white patients, and Asian and Pacific Islander patients had an even greater risk.

Dr. Allareddy acknowledged that the study had some limitations. It was retrospective, and the data used referred to hospitalizations rather than patients. Therefore, key information, such as the severity of the illness, readmissions, and long-term outcomes, was lacking.

After the presentation, an audience member pointed out that most patients with MRSA probably receive prophylactic antibiotics that are ineffective against MRSA. "Should we be screening our preoperative patients to better direct our prophylactic antibiotics?" he asked.

Dr. Allareddy explained that when he and his colleagues analyzed their cohort for patients carrying MRSA at the time of surgery or who had previously been exposed to it, they found only 10,839 cases.

Session moderator David Dries, MD, a critical care surgeon at Regions Hospital in St. Paul, Minnesota, asked whether these exposed patients had more comorbidities.

"Absolutely," Dr. Allareddy said. "And if you have a history of MRSA infection, you have an increased risk of having a MRSA infection after a subsequent procedure."

Dr. Allareddy and Dr. Dries have disclosed no relevant financial relationships.

Society of Critical Care Medicine (SCCM) 43rd Critical Care Congress: Abstract 43. Presented January 10, 2014.


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