Photo: Acinetobacter on MacConkey by Iqbal Osman.
Guest bloggers Dr. Rossana Rosa and Dr Silvia Munoz-Price write: The relationship between patients and their hospital environment is obvious yet intangible. What do we mean by environment? We are talking about the room, and objects within the room such as bedside tables, bedrails and IV pumps. In our study, which was published in the recent ICHE special edition, we found when patients are exposed to rooms contaminated with Acinetobacter baumannii they have an increased risk of acquiring this organism during their index admission. This association remained strong even after controlling for other variables.
In a previous study1, we addressed the other side of the equation, and reported the high degree of contamination detected in the rooms of A. baumannii positive patients. We found that the paired isolates had similarity by PFGE of at least 94.8% with each other, thus suggesting a direct contamination of the environment from the A. baumannii positive patient occupying the room. Put in perspective, the results of these two studies highlight how close, dynamic and interactive is the association between patients and the hospital environment.
Interestingly, we found two variables to be ‘effect modifiers’. An effect modifier is a variable that differentially modifies the observed association between an exposure and an outcome. Despite finding a very strong association between exposure to a contaminated environment and acquisition of A. baumannii in the whole cohort, this association was rendered non-significant when evaluated in sub-groups admitted either to a unit with high colonization pressure or admitted to the trauma intensive care unit. This is relevant because colonization pressure has been shown to play a role in the horizontal transmission of CRE2, as well as VRE3, MRSA4 and C. difficile5. This poses the question of whether contamination of the environment could be primarily a result of the colonization pressure within a unit, to the extent of reaching a threshold after which most of the surfaces in a unit will be contaminated.
The good news is that the exposure to a contaminated environment should be a modifiable risk factor for the acquisition of CRE and MDRO. Active surveillance cultures can be performed to screen for carriers, colonization pressures can then be estimated for each unit, and high touch surfaces can be determined and targeted for cleaning.
1. Munoz-Price LS, Namias N, Cleary T, et al. Acinetobacter baumannii: association between environmental contamination of patient rooms and occupant status. Infect Control Hosp Epidemiol 2013;34:517-520.
2. Swaminathan M, Sharma S, Poliansky Blash S, et al. Prevalence and risk factors for acquisition of carbapenem-resistant Enterobacteriaceae in the setting of endemicity. Infect Control Hosp Epidemiol. 2013;34:809-817.
3. Bonten MJ, Slaughter S, Ambergen AW, et al. The role of “colonization pressure” in the spread of vancomycin-resistant enterococci: an important infection control variable. Arch Internal Med 1998;158:1127-1132.
4. Merrer J, Santoli F, Appere de Vecchi C, Tran B, De Jonghe B, Outin H. “Colonization pressure” and risk of acquisition of methicillin-resistant Staphylococcus aureus in a medical intensive care unit. Infect Control Hosp Epidemiol 2000;21:718-723.
5. Lawrence SJ, Puzniak LA, Shadel BN, Gillespie KN, Kollef MH, Mundy LM. Clostridium difficile in the intensive care unit: epidemiology, costs, and colonization pressure. Infect Control Hosp Epidemiol 2007;28:123-130.
Dr. Silvia Munoz-Price is an Associate Professor of Clinical Medicine at the University of Miami. Dr. Rossana Rosa is currently an Internal Medicine Resident at Miami Miller School of Medicine and an incoming fellow of Infectious Diseases at the same institution. She hopes to continue developing her career in Hospital Epidemiology and Infection Control.