Factors Associated with the Development of Antibiotic-Resistant Bacteria

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The summary below is from the full report titled "The Effect of Vancomycin and Third-Generation Cephalosporins on Prevalence of Vancomycin-Resistant Enterococci in 126 U.S. Adult Intensive Care Units." It is in the 7 August 2001 issue of Annals of Internal Medicine (volume 135, pages 175-183). The authors are SK Fridkin, JR Edwards, JM Courval, H Hill, FC Tenover, R Lawton, RP Gaynes, and JE McGowan Jr., for the Intensive Care Antimicrobial Resistance Epidemiology (ICARE) Project and the National Nosocomial Infections Surveillance (NNIS) System Hospitals.

What is the problem and what is known about it so far?

Unnecessary use of antibiotics is thought to be an important cause of bacterial resistance to antibiotics. One type of bacteria known as vancomycin-resistant enterococci (VRE), which is usually found in the bowel, can cause serious or fatal infections and is extremely difficult to treat. Limited information is available on exactly where VRE occur in hospitals and what factors are associated with their presence.

Why did the researchers do this particular study?

To evaluate how patterns of antibiotic use affected the frequency of finding VRE in hospital intensive care units (ICUs).

Who participated in the study?

Information for this study came from 126 ICUs in 60 hospitals participating in a U.S. nationwide surveillance project examining hospital-acquired infection.

What did the researchers do?

Participating hospitals provided monthly data on hospital-acquired infection. They also reported the type and amount of antibiotics used and whether bacteria found in specimens from hospitalized patients were susceptible to those antibiotics. Data on bacteria were grouped for each ICU, for all non-ICU inpatient units, and for all outpatient areas of the hospital combined. The antibiotics used were grouped according to type.

What did the researchers find?

Ten percent of the bacterial enterococci isolated from these ICU patients were resistant to vancomycin. VRE were found more often at major teaching centers (12.6%) than at nonteaching hospitals (5.6%), and also more often at large hospitals (12.5%) than small ones (5.0%). Antibiotics were used the most in medical ICUs, medical–surgical units, and general surgical units and were used the least in coronary care units, neurosurgical units, and cardiothoracic ICUs (except for vancomycin itself, which was frequently used in neurosurgical and cardiothoracic ICUs). The factor most often associated with the presence of VRE in ICUs was the frequency of VRE in non-ICU inpatient areas of the hospital. The frequency of VRE was greater in ICUs with higher use of vancomycin. Use of another group of antibiotics known as third-generation cephalosporins was also significantly associated with the presence of VRE but only at the highest levels of use. In contrast, the frequency of finding VRE increased steadily as vancomycin use increased (rather than only at very high use levels).

What are the limitations of this study?

The study was not designed to detect the direct spreading of VRE from one patient to another in an ICU and therefore could not distinguish between an epidemic and the effect of antibiotic use. Also, while the researchers studied the entire ICU environment, they could not evaluate individual patients in that environment, nor could they determine the clinical importance of finding VRE.

What are the implications of the study?

The use of certain antibiotics (vancomycin and third-generation cephalosporins) in hospital ICUs is associated with finding VRE. The emergence of VRE in the ICU may be prevented by modifying antibiotic-prescribing habits.