Transmission of Antibiotic-Resistant Bacteria Linked to Previous ICU Room Occupants

Staying in a room in the intensive care unit previously occupied by a patient with treatment-resistant bacteria may increase the odds of acquiring such bacteria, according to a report in the October 9 issue of Archives of Internal Medicine.

Two particular microorganisms cause significant illness and death in hospitals: methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE), according to background information in the article. Researchers previously found that 29 percent of patients who acquire these pathogens develop infections or other complications within 18 months. Floors, beds, gowns, faucets and other hospital room fixtures are persistently contaminated with these bacteria, but it is not known whether levels of the bacteria are high enough to infect additional patients or whether currently mandated cleaning practices are effective in reducing bacterial spread. Although high-risk rooms may exist because of difficult-to-clean design or poor placement of hand hygiene equipment, transmission may be more directly linked to a prior occupant who harbors a resistant organism rather than to a particular room, the authors write.

Susan S. Huang, MD, MPH, of Brigham and Womens Hospital and Harvard Medical School in Boston, and colleagues conducted a 20-month study of 8,203 patients who had 11,528 stays in eight ICUs between 2003 and 2005. As part of the hospitals normal protocols, cultures were obtained from all ICU patients when they arrived and every week they stayed to determine the presence of MRSA and VRE.

Upon entering the ICU, 809 patients carried MRSA and 658 carried VRE, leaving 7,629 to screen for the acquisition of MRSA and 7,806 for acquisition of VRE. The average patient age was 61 years, and 58 percent were male. Fourteen percent of these ICU patients stayed in rooms in which the prior occupant had MRSA and 13 percent stayed in rooms in which the prior occupant had VRE. Those who stayed in rooms after patients with one of the types of bacteria were more likely to acquire that type of bacteria than those who stayed in rooms following patients who did not test positive for that bacteria (4.5 percent vs. 2.8 percent for VRE and 3.9 percent vs. 2.9 percent for MRSA). The excess risk associated with an infected prior occupant accounted for 5.1 percent of all new cases of MRSA and 6.8 percent of all new cases of VRE.

This additional risk occurred despite the fact that the room cleaning procedures of the hospital in the study exceed national guidelines, indicating that such guidelines do not prevent transmission of disease-causing bacteria. However, the low overall risk among patients exposed to the bacteria suggests that levels of contamination do not pose a high risk for transmission or that current cleaning methods generally reduce contamination below levels required for transmission, the authors write. Based on our findings, the prevention of one case of acquisition due to room contamination could require more intensive cleaning of 94 rooms vacated by MRSA carriers and of 59 rooms vacated by VRE carriers.

Though the number of cases attributed to previous room occupants was small, this type of transmission could become more common as the prevalence of treatment-resistant bacteria continues to rise. Additional data are needed to determine whether more intensive cleaning practices can reduce the risk further and, if so, whether this is worthwhile in a resource-limited system, the authors conclude.

Reference: Arch Intern Med. 2006;166:1945-1951.

Source: American Medical Association