Ecology of Pseudomonas aeruginosa in the intensive care unit and the evolving role of water outlets as a reservoir of the organism
Section snippets
The changing microbial spectrum of infections in intensive care
The last 2 decades have witnessed significant changes in the spectrum of microorganisms causing nosocomial infections. Gram-negative enterobacteria, which in the 1970s and 1980s accounted for 30% to 50% of all disease-associated isolates in ICUs,2, 3 have been to a large extent replaced by gram-positive microorganisms such as staphylococci, enterocci, and corynebacteria.4, 5 The relative decrease of infections because of enterobacteria has been achieved by the successful implementation, in most
Role of Pseudomonas aeruginosa
In spite of these significant changes, P aeruginosa has held a nearly unchanged position in the rank order of pathogens causing ICU-related infections for more than 4 decades. In the newest US National Nosocomial Infections Surveillance (NNIS) system report, P aeruginosa continues to represent the third most frequent organism associated with wound or pulmonary infections, the fourth most frequent organism causing urinary tract infection, and the fifth most frequent organism isolated from blood
Antibiotic resistance of P aeruginosa and treatment costs
Of particular concern is the increasing antibiotic resistance of P aeruginosa isolated from ICUs. NNIS data show a rise of resistance rates against commonly used antibiotics such as imipenem, ciprofloxacin, and ceftazidime by 15%, 9%, and 20%, respectively, between the periods 1998-2002 and 2003.11 Data from a single center in Denver, Colorado, showed a dramatic increase of resistance by more than 30% for fluoroquinolones, tobramycin, and imipenem.19 Multiresistance, defined as resistance to >3
Epidemiologic typing of P aeruginosa
Given the fact that P aeruginosa was discovered more than 100 years ago and that a multitude of scientific studies have dealt with the clinical manifestations, antibiotic resistance, and virulence factors of the organism, it is astonishing that relatively little insight into its reservoirs and transmission pathways has been gained. In contrast to gram-negative enterobacteria, no broadly applicable concept for the prevention of P aeruginosa infections has yet been developed.
One of the reasons
Reservoirs and modes of transmission
Using molecular methods, horizontal strain transmissions were proven to be one of the most frequent causes of acquisition of P aeruginosa in the ICU. A series of carefully performed studies examining the epidemiology of P aeruginosa came from a group of researchers from The Netherlands. In their first study, Bergmans et al described the sequence of colonization in 10 ICU patients later diagnosed with VAP.40 Sequential samples taken from the oropharynx, trachea, stomach, and rectum were
Occurrence of P aeruginosa in moist habitats
P aeruginosa is known to thrive well in moist and humid habitats in which the organism can multiply to large numbers, even in the presence of minimal amounts of nutrients. The organism is also a common constituent of polymicrobial biofilms in plumbing systems and drain pipes. In the era of classical typing methods, numerous attempts have been made to identify relationships between disease-associated and waterborne strains.21, 23, 24, 25 However, both because of the variability of classical
Molecular typing data pointing to tap water as a source of P aeruginosa
Studies using molecular typing techniques and comparing water and patient isolates were first initiated in the early 1990s. Tredget et al39 studied an outbreak of wound, respiratory, and bloodstream infections causing significant morbidity in a burn unit in Canada. As demonstrated by pilin gene typing, the strains infecting 59 patients were found to belong to a single genotye that was also detected in hydrotherapy tanks used for immersion of patients. After cessation of hydrotherapy, the strain
Methodologic aspects of testing for P aeruginosa
For future studies of this kind, it will be essential to use a standardized and sensitive technique for the investigation of taps and running water. The study by Blanc et al shows that examining small volumes of water is less sensitive than performing swabs from the inside of outlets.35 We recommend the following procedure for sampling water that proved to be very sensitive in our studies: (1) take water from tap to be examined during a period of less intense use, eg, at 7 am on Monday mornings
Mechanical cleaning of taps and aerators
Uniformly, the above-mentioned studies showed that P aeruginosa colonization of water taps was not a matter of microbial contamination of drinking water supplied by the mains. The microorganism probably gains access to the taps by retrograde contamination, thereafter establishing itself deeply in the bushings of the aerator and mixing valves and in niches and threads of fittings and fixtures. Strategies to keep the organism at low densities should always include careful cleaning and regular
The concept of point-of-use water filtration
In our own study of the surgical ICU of a teaching hospital, we observed approximately 5 to 10 cases of P aeruginosa infection or colonization per month, along with uniformly positive tap water cultures. On this ward, we decided to start a program of point-of-use water filtration using disposable tap-mounted filters used for 7 days. Filtered water proved to be always sterile after mounting the filters. Thereafter, the number of infections and colonizations fell constantly, reaching a level of 1
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