Surgeons Find That Drug-Resistant Infections Not Always Linked to Higher Death Rates

The rates of antibiotic-resistant infections in the intensive care unit (ICU) have increased over the last decade. But new research from the University of Virginia suggests that surgical ICU death rates may, in fact, be declining and that drug-resistant infections are not likely to be a significant factor in overall mortality rates. These findings were reported at the 2011 Annual Clinical Congress of the American College of Surgeons.

Healthcare-associated infections (HAIs), from all types of bacteria combined, occur in 1.7 million patients each year, and rank among the top 10 leading causes of death in the United States, according to the Department of Health and Human Services. In addition, surgical site infections account for approximately 15 percent of hospital-associated acute care infections.

The overuse and misuse of antibiotics and other anti-infective medications enables bacteria and viruses to develop drug resistance. Over the years, drug resistance has become a problem that has made it harder to fight off patient infections with the drugs commonly used as a treatment.

In an effort to understand whether ICU drug-resistance is associated with an increase in overall mortality, a team of researchers including Laura Horst Rosenberger, MD, MS, a research fellow in the department of surgery at the University of Virginia, Charlottesville, conducted a database analysis on all infections acquired in a single surgical/trauma ICU between 2000 and 2010. The analysis included all-cause mortality rates.

Specifically, the researchers identified 799 resistant pathogens associated with 1,493 ICU-acquired infections. A statistical analysis, comparing trends of drug-resistant infections to death rates of patients who had infectious complications in the ICU, revealed that while rates of drug-resistant infections increased during the 10-year study period, all-cause mortality rates for patients from this single surgical ICU actually fell by four percent. Their results were surprisingly positive.

The bottom line is that we think that these patients who have infection are not dying from that infection after all; however, they die with that infection because, for example, they are of advanced age and suffered multiple traumatic injuries resulting in high injury severity scores and high acute physiology scores, Rosenberger explains. Patients with the highest risk of infections (elderly, admitted to the ICU, multiple previous co-morbidities, ventilator dependence, previous antibiotic exposure, and so on) generally have the most poor prognosis to begin with. The hospital-acquired infections preferentially affect the most vulnerable patients and the mortality attributable to the infection is relatively small.

In addition, the researchers found that the most common Gram-positive and Gram-negative pathogens were methicillin- resistant Staphylococcus aureus (MSRA) and Pseudomonas aeruginosa, respectively. And the most common sites of infection were in the lung, blood, and urine. Most studies analyzing resistant bacterial infections have looked at all patients with infections, but they do not distinguish the actual microorganism or control for severity of disease of the patient, Rosenberger says. This study underscores the idea that these resistant infections are opportunistic, affecting those with the highest severity of illness.

Under increasing pressure to reduce HAIs, hospitals are working to establish new processes to prevent these infections from occurring in the first place. Antimicrobial resistance is not a new public health concern, but has been reported as far back as the early 1960s. Methicillin was first introduced in 1959 and merely two years later reports of methicillin-resistant Staphylococcus aureus (MRSA) were being published, Rosenberger says. While it definitely requires our attention and diligence as well as preventive measures such as handwashing and prevention of patient-to-patient transmission, I think the message of our study is that rising numbers of resistant infections are not resulting in higher overall mortality rates.

And while the researchers are careful to note that their findings only show a correlation from a single surgical ICU unit, they believe that most institutions would find similar results if they looked at their overall mortality rates in the ICU. We believe the patients who are acquiring the resistant infections are likely dying with their infections and not by those infections, Rosenberger says.

Further research is needed to expand these conclusions. We continue to improve critical care and learn new techniques and methods for improved outcomes, Rosenberger adds. We certainly have a greater severity of illness in our patient population over time and therefore do not believe the improved mortality rates are due to less sick patients.

Other participants on the study include Damien J. LaPar, MD and faculty mentor, Robert G. Sawyer MD, FACS.