Patients with Pseudomonas aeruginosa Serve as Reservoirs for Environmental Contamination

Studies of recent hospital outbreaks caused by multidrug-resistant P. aeruginosa (MRPA) have often failed to identify a specific environmental reservoir. Cristina Suarez, of the Infectious Diseases Service at Hospital Universitari de Bellvitge, University of Barcelona, Barcelona, Spain, and colleagues, describe an outbreak due to a single clone of MRPA and evaluate the effectiveness of the surveillance procedures and control measures applied.

Patients with MRPA isolates were prospectively identified (January 2006 through May 2008). A combined surveillance procedure (environmental survey of high-touch objects, and active surveillance program in intensive care units [ICUs]) and an infection control strategy (closure of ICU and urology wards for decontamination, strict compliance with cross-transmission prevention protocols, and a program restricting the use of carbapenems in the ICUs) was designed and implemented.

Three hundred ninety patients were identified. ICU patients were the most numerous group (22 percent) followed by urology patients (18 percent). Environmental surveillance found that 3/19 (16 percent) non-ICU environmental samples and 4/63 (6 percent) ICU samples were positive for the MRPA clonal strain. In addition, active surveillance found that 19 percent of patients were fecal carriers of MRPA. Significant changes in the trends of incidence rates were noted after intervention 1 (reinforcement of cleaning procedures): -1.16 cases/1,000 patient-days (95%CI -1.86 to -0.46; p = 0.003) and intervention 2 (extensive decontamination): -1.36 cases/1,000 patient-days (95%CI -1.88 to -0.84; p < 0.001) in urology wards. In addition, restricted use of carbapenems was initiated in ICUs (January 2007), and their administration decreased from 190-170 DDD/1,000 patient-days (October-December 2006) to 40-60 DDD/1,000 patient-days (January-April 2007), with a reduction from 3.1 cases/1,000 patient-days in December 2006 to 2.0 cases/1,000 patient-days in May 2007. The level of initial carbapenem use rose again during 2008, and the incidence of MRPA increased progressively once more.

The researchers conclude that in the setting of sustained MRPA outbreaks, epidemiological findings suggest that patients may be a reservoir for further environmental contamination and cross-transmission. They say that although their control program was not successful in ending the outbreak, they think that their experience provides useful guidance for future approaches to this problem. Their research was published in BMC Infectious Diseases. 

Reference: Suarez1 C, et al. A large sustained endemic outbreak of multiresistant Pseudomonas aeruginosa: a new epidemiological scenario for nosocomial acquisition. BMC Infectious Diseases 2011, 11:272 doi:10.1186/1471-2334-11-272