Pseudomonas in the sinks in an intensive care unit: relation to patients

Epidemiology of healthcare-associated Pseudomonas aeruginosa in intensive care units: are sink drains to blame?

BACKGROUND

Pseudomonas aeruginosa (PA) is a common cause of healthcare-associated infection (PA-HAI) in the intensive care unit (ICU).

AIM

To describe the epidemiology of PA-HAI in ICUs in Ontario, Canada, and to identify episodes of sink-to-patient PA transmission.

METHODS

This was a prospective cohort study of patients in six ICUs from 2018 to 2019, with retrieval of PA clinical isolates, and PA-screening of antimicrobial-resistant organism surveillance rectal swabs, and of sink drain, air, and faucet samples. All PA isolates underwent whole-genome sequencing. PA-HAI was defined using US National Healthcare Safety Network criteria. ICU-acquired PA was defined as PA isolated from specimens obtained ≥48 h after ICU admission in those with prior negative rectal swabs. Sink-to-patient PA transmission was defined as ICU-acquired PA with close genomic relationship to isolate(s) previously recovered from sinks in a room/bedspace occupied 3-14 days prior to collection date of the relevant patient specimen.

FINDINGS

Over ten months, 72 PA-HAIs occurred among 60/4263 admissions. The rate of PA-HAI was 2.40 per 1000 patient-ICU-days; higher in patients who were PA-colonized on admission. PA-HAI was associated with longer stay (median: 26 vs 3 days uninfected; P < 0.001) and contributed to death in 22/60 cases (36.7%). Fifty-eight admissions with ICU-acquired PA were identified, contributing 35/72 (48.6%) PA-HAIs. Four patients with five PA-HAIs (6.9%) had closely related isolates previously recovered from their room/bedspace sinks.

CONCLUSION

Nearly half of PA causing HAI appeared to be acquired in ICUs, and 7% of PA-HAIs were associated with sink-to-patient transmission. Sinks may be an under-recognized reservoir for HAIs.

Are Sink Drainage Systems a Reservoir for Hospital-Acquired Gammaproteobacteria Colonization and Infection? A Systematic Review

Increasing rates of antimicrobial-resistant organisms have focused attention on sink drainage systems as reservoirs for hospital-acquired Gammaproteobacteria colonization and infection. We aimed to assess the quality of evidence for transmission from this reservoir. We searched 8 databases and identified 52 studies implicating sink drainage systems in acute care hospitals as a reservoir for Gammaproteobacterial colonization/infection. We used a causality tool to summarize the quality of evidence. Included studies provided evidence of co-occurrence of contaminated sink drainage systems and colonization/infection, temporal sequencing compatible with sink drainage reservoirs, some steps in potential causal pathways, and relatedness between bacteria from sink drainage systems and patients. Some studies provided convincing evidence of reduced risk of organism acquisition following interventions. No single study provided convincing evidence across all causality domains, and the attributable fraction of infections related to sink drainage systems remains unknown. These results may help to guide conduct and reporting in future studies.

Development of a tool to assess evidence for causality in studies implicating sink drains as a reservoir for hospital-acquired gammaproteobacterial infection

BACKGROUND

Decades of studies document an association between Gammaproteobacteria in sink drains and hospital-acquired infections, but the evidence for causality is unclear.

AIM

We aimed to develop a tool to assess the quality of evidence for causality in research studies that implicate sink drains as reservoirs for hospital-acquired Gammaproteobacterial infections.

METHODS

We used a modified Delphi process with recruited experts in hospital epidemiology to develop this tool from a pre-existing causal assessment application.

FINDINGS

Through four rounds of feedback and revision we developed the 'Modified CADDIS Tool for Causality Assessment of Sink Drains as a Reservoir for Hospital-Acquired Gammaproteobacterial Infection or Colonization'. In tests of tool application to published literature during development, mean percent agreement ranged from 46.7% to 87.5%, and the Gwet's AC1 statistic (adjusting for chance agreement) ranged from 0.13 to 1.0 (median 68.1). Areas of disagreement were felt to result from lack of a priori knowledge of causal pathways from sink drains to patients and uncertain influence of co-interventions to prevent organism acquisition. Modifications were made until consensus was achieved that further iterations would not improve the tool. When the tool was applied to 44 articles by two independent reviewers in an ongoing systematic review, percent agreement ranged from 93% to 98%, and the Gwet's AC1 statistic was 0.91-0.97.

CONCLUSION

The modified causality tool was useful for evaluating studies that implicate sink drains as reservoirs for hospital-acquired infections and may help guide the conduct and reporting of future research.

Mitigation of microbial contamination from waste water and aerosolization by sink design

BACKGROUND

Healthcare-associated infections (HAIs) are a significant cause of increased medical costs, morbidity, mortality, and have been partly associated with sinks, their waste water outlets and associated pipework.

AIM

To determine whether an engineered sink could limit microbial aerosol contaminants in the air and sink basin.

METHODS

Multiple comparisons were undertaken between an experimental sink, designed to limit aerosolization and p-trap contamination to a control hospital sink, both connected to a common drain system. The experimental sink was equipped with ultraviolet light (UV), an aerosol containment hood, ozonated water generator and a flush system to limit bacterial growth/aerosolization and limit microbial growth in the p-trap. Nutrient material was added daily to simulate typical material discarded into a hospital sink. Surface collection swabs, settle plates and p-trap contamination levels were assessed for bacteria and fungi.

FINDINGS

The experimental sink had significantly decreased levels of bacterial and fungal p-trap contamination (99.9% for Tryptic Soy (TSA) and Sabouraud agar (SAB) plates) relative to the initial levels. Aerosol-induced contaminant from the p-traps was significantly lower for the experimental vs the control sink for TSA (76%) and SAB (86%) agar settle plates.

CONCLUSIONS

Limiting microbial contamination is critical for the control of nosocomial infections of in-room sinks, which provide a major source of contamination. Our experimental sink studies document that regular ozonated water rinsing of the sink surface, decontamination of p-trap water, and UV decontamination of surfaces limits microbial aerosolization and surface contamination, with potential to decrease patient exposure and reduce hospital acquired infections.

Hospital Drains as Reservoirs of Pseudomonas aeruginosa: Multiple-Locus Variable-Number of Tandem Repeats Analysis Genotypes Recovered from Faucets, Sink Surfaces and Patients

Identifying environmental sources of Pseudomonas aeruginosa (Pa) related to hospital-acquired infections represents a key challenge for public health. Biofilms in water systems offer protection and favorable growth conditions, and are prime reservoirs of microorganisms. A comparative genotyping survey assessing the relationship between Pa strains recovered in hospital sink biofilm and isolated in clinical specimens was conducted. Environmental strains from drain, faucet and sink-surface biofilm were recovered by a culture method after an incubation time ranging from 48 to 240 h. The genotyping of 38 environmental and 32 clinical isolates was performed using a multiple-locus variable-number of tandem repeats analysis (MLVA). More than one-third of Pa isolates were only cultivable following ≥48 h of incubation, and were predominantly from faucet and sink-surface biofilms. In total, 41/70 strains were grouped within eight genotypes (A to H). Genotype B grouped a clinical and an environmental strain isolated in the same ward, 5 months apart, suggesting this genotype could thrive in both contexts. Genotype E grouped environmental isolates that were highly prevalent throughout the hospital and that required a longer incubation time. The results from the multi-hospital follow-up study support the drain as an important reservoir of Pa dissemination to faucets, sink surfaces and patients. Optimizing the recovery of environmental strains will strengthen epidemiological investigations, facilitate pathway identification, and assist in identifying and controlling the reservoirs potentially associated to hospital-acquired infections.

Reduced rate of intensive care unit acquired gram-negative bacilli after removal of sinks and introduction of 'water-free' patient care

Background

Sinks in patient rooms are associated with hospital-acquired infections. The aim of this study was to evaluate the effect of removal of sinks from the Intensive Care Unit (ICU) patient rooms and the introduction of ‘water-free’ patient care on gram-negative bacilli colonization rates.

Methods

We conducted a 2-year pre/post quasi-experimental study that compared monthly gram-negative bacilli colonization rates pre- and post-intervention using segmented regression analysis of interrupted time series data. Five ICUs of a tertiary care medical center were included. Participants were all patients of 18 years and older admitted to our ICUs for at least 48 h who also received selective digestive tract decontamination during the twelve month pre-intervention or the twelve month post-intervention period. The effect of sink removal and the introduction of ‘water-free’ patient care on colonization rates with gram-negative bacilli was evaluated. The main outcome of this study was the monthly colonization rate with gram-negative bacilli (GNB). Yeast colonization rates were used as a ‘negative control’. In addition, colonization rates were calculated for first positive culture results from cultures taken ≥3, ≥5, ≥7, ≥10 and ≥14 days after ICU-admission, rate ratios (RR) were calculated and differences tested with chi-squared tests.

Results

In the pre-intervention period, 1496 patients (9153 admission days) and in the post-intervention period 1444 patients (9044 admission days) were included. Segmented regression analysis showed that the intervention was followed by a statistically significant immediate reduction in GNB colonization in absence of a pre or post intervention trend in GNB colonization. The overall GNB colonization rate dropped from 26.3 to 21.6 GNB/1000 ICU admission days (colonization rate ratio 0.82; 95%CI 0.67–0.99; P = 0.02). The reduction in GNB colonization rate became more pronounced in patients with a longer ICU-Length of Stay (LOS): from a 1.22-fold reduction (≥2 days), to a 1.6-fold (≥5 days; P = 0.002), 2.5-fold (for ≥10 days; P < 0.001) to a 3.6-fold (≥14 days; P < 0.001) reduction.

Conclusions

Removal of sinks from patient rooms and introduction of a method of ‘water-free’ patient care is associated with a significant reduction of patient colonization with GNB, especially in patients with a longer ICU length of stay.

Electronic supplementary material

The online version of this article (doi:10.1186/s13756-017-0213-0) contains supplementary material, which is available to authorized users.

Spread from the Sink to the Patient: In Situ Study Using Green Fluorescent Protein (GFP)-Expressing Escherichia coli To Model Bacterial Dispersion from Hand-Washing Sink-Trap Reservoirs

There have been an increasing number of reports implicating Gammaproteobacteria as often carrying genes of drug resistance from colonized sink traps to vulnerable hospitalized patients. However, the mechanism of transmission from the wastewater of the sink P-trap to patients remains poorly understood. Herein we report the use of a designated hand-washing sink lab gallery to model dispersion of green fluorescent protein (GFP)-expressing Escherichia coli from sink wastewater to the surrounding environment. We found no dispersion of GFP-expressing E. coli directly from the P-trap to the sink basin or surrounding countertop with coincident water flow from a faucet. However, when the GFP-expressing E. coli cells were allowed to mature in the P-trap under conditions similar to those in a hospital environment, a GFP-expressing E. coli-containing putative biofilm extended upward over 7 days to reach the strainer. This subsequently resulted in droplet dispersion to the surrounding areas (<30 in.) during faucet operation. We also demonstrated that P-trap colonization could occur by retrograde transmission along a common pipe. We postulate that the organisms mobilize up to the strainer from the P-trap, resulting in droplet dispersion rather than dispersion directly from the P-trap. This work helps to further define the mode of transmission of bacteria from a P-trap reservoir to a vulnerable hospitalized patient.

IMPORTANCE Many recent reports demonstrate that sink drain pipes become colonized with highly consequential multidrug-resistant bacteria, which then results in hospital-acquired infections. However, the mechanism of dispersal of bacteria from the sink to patients has not been fully elucidated. Through establishment of a unique sink gallery, this work found that a staged mode of transmission involving biofilm growth from the lower pipe to the sink strainer and subsequent splatter to the bowl and surrounding area occurs rather than splatter directly from the water in the lower pipe. We have also demonstrated that bacterial transmission can occur via connections in wastewater plumbing to neighboring sinks. This work helps to more clearly define the mechanism and risk of transmission from a wastewater source to hospitalized patients in a world with increasingly antibiotic-resistant bacteria that can thrive in wastewater environments and cause infections in vulnerable patients.

Formulation of Biocides Increases Antimicrobial Potency and Mitigates the Enrichment of Nonsusceptible Bacteria in Multispecies Biofilms

The current investigation aimed to generate data to inform the development of risk assessments of biocide usage. Stabilized domestic drain biofilm microcosms were exposed daily over 6 months to increasing concentrations (0.01% to 1%) of the biocide benzalkonium chloride (BAC) in a simple aqueous solution (BAC-s) or in a complex formulation (BAC-f) representative of a domestic cleaning agent. Biofilms were analyzed by culture, differentiating by bacterial functional group and by BAC or antibiotic susceptibility. Bacterial isolates were identified by 16S rRNA sequencing, and changes in biofilm composition were assessed by high-throughput sequencing. Exposure to BAC-f resulted in significantly larger reductions in levels of viable bacteria than exposure to BAC-s, while bacterial diversity greatly decreased during exposure to both BAC-s and BAC-f, as evidenced by sequencing and viable counts. Increases in the abundance of bacteria exhibiting reduced antibiotic or BAC susceptibility following exposure to BAC at 0.1% were significantly greater for BAC-s than BAC-f. Bacteria with reduced BAC and antibiotic susceptibility were generally suppressed by higher BAC concentrations, and formulation significantly enhanced this effect. Significant decreases in the antimicrobial susceptibility of bacteria isolated from the systems before and after long-term BAC exposure were not detected. In summary, dose-dependent suppression of bacterial viability by BAC was enhanced by formulation. Biocide exposure decreased bacterial diversity and transiently enriched populations of organisms with lower antimicrobial susceptibility, and the effects were subsequently suppressed by exposure to 1% BAC-f, the concentration most closely reflecting deployment in formulated products.IMPORTANCE Assessment of the risks of biocide use has been based mainly on the exposure of axenic cultures of bacteria to biocides in simple aqueous solutions. The current investigation aimed to assess the effects of formulation on the outcome of biocide exposure in multispecies biofilms. Formulation of the cationic biocide BAC significantly increased antimicrobial potency. Bacteria with lower antimicrobial susceptibility whose populations were enriched after low-level biocide exposure were more effectively suppressed by the biocide at in-use concentrations (1% [wt/vol]) in a formulation than in a simple aqueous solution. These observations underline the importance of simulating normal deployment conditions in considering the risks and benefits of biocide use.

Flowers in the clinical setting: Infection risk or workload issue?

Healthcare-associated infection has become a topic of interest to the general public in the United Kingdom, kindled by media accounts of poor hygiene and the risks of cross-infection. In the spring of 2003, one of the broadsheet newspapers published an article debating the hygiene and infection risks associated with cut flowers brought into clinical areas. There were reports that in many wards this practice is no longer allowed because flowers are considered dirty, trigger allergies and the water is regarded as harbouring bacteria, leading to infection.

Discussion with infection control experts revealed that questions concerning the risks associated with flowers are among those most frequently asked. A literature search was undertaken to establish the evidence base, and a questionnaire study was performed with a purposive sample of 39 nurses to document how they manage flowers in the clinical setting. Empirical research studies were difficult to obtain. Early work had been undertaken to explore the added workload associated with maintaining fresh flowers and ways of reducing it. Later studies revealed that the water in flower vases and cut plants both harbour large numbers of Gram-negative pathogens.

Cross-infection and cases of clinical infection have never been documented, thus flowers have not been considered a risk, except to severely immunocompromised patients. However, scrutiny of the more general literature relating to Gram-negative sepsis indicated that cross-infection has been documented from a wide range of environmental sources and it is possible that it may take place from flowers via the hands of staff if they are not properly decontaminated. Nevertheless, these risks can be reduced by scrupulous attention to hand hygiene and commonsense measures.

Over half the nurses (n = 26, 66.6%) thought that flowers constituted an infection risk and a number of other disadvantages were cited. Most nurses (n = 31, 80%) were not in favour of flowers in the clinical setting and there was some evidence that this attitude was related to the amount of work generated, with infection and other risks used to justify it. Interest in the topic was considerable and the results can be used to stimulate discussion and emphasise the importance of controlling health-related infection.

Pseudomonas aeruginosa in premise plumbing of large buildings

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that is widely occurring in the environment and is recognized for its capacity to form or join biofilms. The present review consolidates current knowledge on P. aeruginosa ecology and its implication in healthcare facilities premise plumbing. The adaptability of P. aeruginosa and its capacity to integrate the biofilm from the faucet and the drain highlight the role premise plumbing devices can play in promoting growth and persistence. A meta‐analysis of P. aeruginosa prevalence in faucets (manual and electronic) and drains reveals the large variation in device positivity reported and suggest the high variability in the sampling approach and context as the main reason for this variation. The effects of the operating conditions that prevail within water distribution systems (disinfection, temperature, and hydraulic regime) on the persistence of P. aeruginosa are summarized. As a result from the review, recommendations for proactive control measures of water contamination by P. aeruginosa are presented. A better understanding of the ecology of P. aeruginosa and key influencing factors in premise plumbing are essential to identify culprit areas and implement effective control measures.

Sources of sporadic Pseudomonas aeruginosa colonizations/infections in surgical ICUs: Association with contaminated sink trap

BACKGROUND

Many studies have reported the hospital outbreaks of Pseudomonas aeruginosa due to cross-contamination between patients and water fittings, but the importance of water fittings as sources of sporadic P. aeruginosa colonizations/infections remains ambiguous.

AIM

To investigate the sources of sporadic P. aeruginosa colonizations/infections in a clinical intensive surveillance, and further analysis the potential of sink trap for P. aeruginosa transmission in intensive care units (ICUs).

METHODS

Patients monitoring and targeted environmental screening for P. aeruginosa was performed prospectively over a 27-week period, in absence of recognized outbreak, in two surgical intensive care units (SICUs). All isolates were genotyped by Pulsed field gel electrophoresis analysis.

FINDINGS

18.9% (46/244) of water fitting samples harbored P. aeruginosa, and active screening samples from 9.2% (55/595) of hospitalized patients carried with P. aeruginosa. According to genotype results, approximately 50% of P. areuginosa colonizations/infections of patients were of exogenous origin. 64.7% (11/17) of exogenous sourced cases were associated with contaminated sink traps. There was a significant correlation between the incidence of exogenous colonization/infection and the prevalence of P. areuginosa in water fitting in SICU-2 (rs = 0.972; p = 0.014). Furthermore, P. areuginosa from sink trap possessed a higher level of resistance to multi-antibiotics as opposed to cross-transmission from other patients.

CONCLUSION

Water fitting especially sink trap act as an important role in sporadic P. aeruginosa transmission in SICU patients. This report highlights the necessity of identification of potential environmental reservoirs, such as sinks, for control of infections of environmentally hardy multi-resistant P. areuginosa.

Self-disinfecting sink drains reduce the Pseudomonas aeruginosa bioburden in a neonatal intensive care unit

AIM

Water in sink drains is a known source of gram-negative bacteria. We aimed to evaluate the impact of self-disinfecting sink drains on the emission of aerosolised bacteria and on Pseudomonas aeruginosa acquisition among neonates.

METHODS

Aerosol bacterial growth and patient Pseudomonas aeruginosa acquisition rates were measured at baseline (Phase One), for 13 months after sinks were relocated or redesigned during refurbishment (Phase Two) and for 13 months after introducing self-disinfecting sink drains (Phase Three).

RESULTS

Cultures were positive for bacterial growth in 56%, 24% and 13% of the tested aerosols in Phases One, Two and Three, respectively. Comparing Phases Two and Three produced an odds ratio (OR) of 0.47, with a 95% confidence interval (CI) of 0.22-0.99 (p = 0.047), for all bacteria and an OR of 0.31 and CI of 0.12-0.79 (p = 0.013) for Pseudomonas aeruginosa. Rates of Pseudomonas aeruginosa positive clinical cultures were 0.34, 0.27 and 0.13 per 1000 patient days during the respective phases, with a significant increase of time to the next positive clinical culture in Phase Three.

CONCLUSION

Self-disinfecting sink drains were superior to sink replacements in preventing emissions from aerosols pathogens and may reduce hospital-acquired infections. The bioburden reduction should be confirmed in a larger multicentre trial.

Whole Genome Sequencing in Real-Time Investigation and Management of a Pseudomonas aeruginosa Outbreak on a Neonatal Intensive Care Unit

OBJECTIVE

To use whole genome sequencing to describe the likely origin of an outbreak of Pseudomonas aeruginosa in a neonatal unit.

DESIGN

Outbreak investigation.

SETTING

The neonatal intensive care unit service of a major obstetric tertiary referral center.

PATIENTS

Infants admitted to the neonatal unit who developed P. aeruginosa colonization or infection.

METHODS

We undertook whole genome sequencing of P. aeruginosa strains isolated from colonized infants and from the neonatal unit environment.

RESULTS

Eighteen infants were colonized with P. aeruginosa. Isolates from 12 infants and 7 environmental samples were sequenced. All but one of the clinical isolates clustered in ST253 and no differences were detected between unmapped reads. The environmental isolates revealed a variety of sequence types, indicating a large diverse bioburden within the unit, which was subsequently confirmed via enterobacterial repetitive intergenic consensus-polymerase chain reaction typing of post-outbreak isolates. One environmental isolate, obtained from a sink in the unit, clustered within ST253 and differed from the outbreak strain by 9 single-nucleotide polymorphisms only. This information allowed us to focus infection control activities on this sink.

CONCLUSIONS

Whole genome sequencing can provide detailed information in a clinically relevant time frame to aid management of outbreaks in critical patient management areas. The superior discriminatory power of this method makes it a powerful tool in infection control.

Drainage systems, an occluded source of sanitation related outbreaks

BACKGROUND

Drainage systems and its role in sanitation related outbreaks are evident but still occluded once it has been installed. This current review evaluates if drainage systems can cause infections and thus be of clinical concern.

METHOD

A review of the literature was analyzed. Papers, guidelines, and quality management systems have been considered.

RESULTS

Adequate sanitation is fundamental and a prerequisite for safe life and productivity. In contrast, malfunctioning sanitation has been reported to cause outbreaks all over the world. In areas with no sanitation, diarrheal mortality is high and has been shown to decrease by 36% after interventions to improve sanitation. Often, infections are faeces associated and when present in wastewater and sewage sludge poses a high risk of infection upon exposure. Hence, there are working safety guidelines and in industries where infection reduction is essential strict quality assurance systems, i.e. HACCP (hazard analysis critical control points) and GMP (Good Manufacturing Practice) must be complied. Healthcare has recently taken interest in the HACCP system in their efforts to reduce healthcare associated infections as a response to increasing number of ineffective antibiotics and the threat of mortality rate like the pre-antibiotic era. The last few years have called for immediate action to contain the emergence of increasing resistant microorganisms. Resistance is obtained as a result of overuse and misuse of antibiotics in both healthcare and agriculture. Also, by the discharge of antibiotics from manufacturers, healthcare and society. One mechanism of development of novel resistant pathogens has been shown to be by effortless sharing of genetic mobile elements coding for resistance from microbes in the environment to human microbes. These pathogens have been sampled from the drainage systems. These were noticed owing to their possession of an unusual antibiotic resistance profile linking them to the outbreak. Often the cause of sanitation related outbreaks is due to inadequate sanitation and maintenance. However, in general these infections probably go unnoticed.

CONCLUSION

Drainage systems and its maintenance, if neglected, could pose a threat in both community and healthcare causing infections as well as emergence of multi-resistant bacteria that could cause unpredictable clinical manifestations.

Outbreak of Multidrug-ResistantPseudomonas aeruginosaColonization and Infection Secondary to Imperfect Intensive Care Unit Room Design

Background.

Pseudomonas aeruginosahas been increasingly recognized for its ability to cause significant hospital-associated outbreaks, particularly since the emergence of multidrug-resistant strains. Biofilm formation allows the pathogen to persist in environmental reservoirs. Thus, multiple hospital room design elements, including sink placement and design, can impact nosocomial transmission ofP. aeruginosaand other pathogens.

Methods.

From December 2004 through March 2006, 36 patients exposed to the intensive care unit or transplant units of a tertiary care hospital were infected with a multidrug-resistant strain ofP. aeruginosa. All phenotypically similar isolates were examined for genetic relatedness by means of pulsed-field gel electrophoresis. Clinical characteristics of the affected patients were collected, and a detailed epidemiological and environmental investigation of potential sources was carried out.

Results.

Seventeen of the infected patients died within 3 months; for 12 (71%) of these patients, infection with the outbreak organism contributed to or directly caused death. The source of the outbreak was traced to hand hygiene sink drains, where biofilms containing viable organisms were found. Testing by use of a commercial fluorescent marker demonstrated that when the sink was used for handwashing, drain contents splashed at least 1 meter from the sink. Various attempts were made to disinfect the drains, but it was only when the sinks were renovated to prevent splashing onto surrounding areas that the outbreak was terminated.

Conclusion.

This report highlights the importance of biofilms and of sink and patient room design in the propagation of an outbreak and suggests some strategies to reduce the risks associated with hospital sinks.

The Role of Water in the Transmission of Healthcare-Associated Infections: Opportunities for Intervention through the Environment

OBJECTIVE:

To assess and synthesize available evidence in the infection control and healthcare design literature on strategies using the built environment to reduce the transmission of pathogens in water that cause healthcare-associated infections (HAIs).

BACKGROUND:

Water can serve as a reservoir or source for pathogens, which can lead to the transmission of healthcare-associated infections (HAIs). Water systems harboring pathogens, such as Legionella and Pseudomonas spp., can also foster the growth of persistent biofilms, presenting a great health risk.

TOPICAL HEADINGS:

Strategies for interrupting the chain of transmission through the built environment can be proactive or reactive, and include three primary approaches: safe plumbing practices (maintaining optimal water temperature and pressure; eliminating dead ends), decontamination of water sources (inactivating or killing pathogens to prevent contamination), and selecting appropriate design elements (fixtures and materials that minimize the potential for contamination).

CONCLUSIONS:

Current evidence clearly identifying the environment's role in the chain of infection is limited by the variance in surveillance strategies and in the methods used to assess impact of these strategies. In order to optimize the built environment to serve as a tool for mitigating infection risk from waterborne pathogens—from selecting appropriate water features to maintaining the water system—multidisciplinary collaboration and planning is essential.

Pseudomonas in augmented care: should we worry?

The problem of Pseudomonas as a nosocomial pathogen is not new, with some authors dating its onset to the start of the antimicrobial era, although other factors, such as the growth of intensive or augmented care, have a part to play. This paper outlines the historical and environmental issues that may be associated with a potential increase in the incidence of this difficult-to-treat pathogen.

Multidrug-resistant Pseudomonas aeruginosa outbreaks in two hospitals: association with contaminated hospital waste-water systems

BACKGROUND

Multidrug-resistant Pseudomonas aeruginosa (MDR-P) expressing VIM-metallo-beta-lactamase is an emerging infection control problem. The source of many such infections is unclear, though there are reports of hospital outbreaks of P. aeruginosa related to environmental contamination, including tap water.

AIM

We describe two outbreaks of MDR-P, sensitive only to colistin, in order to highlight the potential for hospital waste-water systems to harbour this organism.

METHODS

The outbreaks were investigated by a combination of descriptive epidemiology, inspection and microbiological sampling of the environment, and molecular strain typing.

FINDINGS

The outbreaks occurred in two English hospitals; each involved a distinct genotype of MDR-P. One outbreak was hospital-wide, involving 85 patients, and the other was limited to four cases in one specialized medical unit. Extensive environmental sampling in each outbreak yielded MDR-P only from the waste-water systems. Inspection of the environment and estates records revealed many factors that may have contributed to contamination of clinical areas, including faulty sink, shower and toilet design, clean items stored near sluices, and frequent blockages and leaks from waste pipes. Blockages were due to paper towels, patient wipes, or improper use of bedpan macerators. Control measures included replacing sinks and toilets with easier-to-clean models less prone to splashback, educating staff to reduce blockages and inappropriate storage, reviewing cleaning protocols, and reducing shower flow rates to reduce flooding. These measures were followed by significant reductions in cases.

CONCLUSION

The outbreaks highlight the potential of hospital waste systems to act as a reservoir of MDR-P and other nosocomial pathogens.

Contaminated feeding bottles: the source of an outbreak of Pseudomonas aeruginosa infections in a neonatal intensive care unit

BACKGROUND

Outbreaks of Pseudomonas aeruginosa have been reported in relationship with contamination of staff fingernails, hands, water baths, hand lotions and others. To our knowledge, contamination of milk and feeding bottles as a source of an outbreak of P aeruginosa infections has not been reported. The incidence of P aeruginosa infection/colonization in our neonatal intensive care unit increased from 1.9 per 1000 patient-days in August 2004 to 8.8 per 1000 patient-days in September 2004.

METHODS

Samples were collected including hand and body lotions, water from the incubator humidifying system, the health care worker hands, and the feeding bottle preparation room. Strains were epidemiologically characterized by pulsed-field gel electrophoresis of SpeI-digested genomic DNA. P aeruginosa was isolated from a total of 30 neonates during the period September 2004 to December 2004.

RESULTS

All cultures (139) of hand and body lotions, water from the incubator humidifying system, and hands of health care personnel were negative. Nine out of 48 samples collected from the feeding bottle preparation room were positive for P aeruginosa (6 samples of in-house prepared milk and 3 samples of water from dishwashers). Pulsed-field gel electrophoresis with SpeI showed that the strains isolated from neonates and from environmental samples were identical. Discontinuation of in-house preparation of feeding bottles and incorporation of unidose milk bottles stopped the outbreak.

CONCLUSION

The preparation and solution of milk from multidose powder preparation may be a source of P aeruginosa infections in a neonatal intensive care unit. The use of manufactured, nonmanipulated, unidose feeding bottles should be considered more adequate.

Common RAPD pattern of Pseudomonas aeruginosa from patients and tap water in a medical intensive care unit

The epidemiology of Pseudomonas aeruginosa infections and colonizations was studied prospectively on a 12-bed medical intensive care unit. Patients were monitored for P. aeruginosa colonization by performing throat swabs or tracheal aspirates on admission and weekly thereafter over a period of 6 months. Cultures of possibly infected sites were taken as clinically indicated. Water samples from all patient care-related tap water outlets were collected in 2-weekly intervals and examined for the presence of P. aeruginosa. Strains isolated from patients and water samples were analysed by serotyping and random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) typing. During the 6-month period, 60 of 143 (42%) water samples contained P. aeruginosa at various levels ranging from 1 to >100 colony-forming units per 100ml sample. Genotypically, water samples contained 8 different clonotypes. Nine patients had infections due to P. aeruginosa and 7 patients were colonized. Isolates from patients showed a similar distribution of genotypes as did tap water isolates, and strains of identical genotype as patient strains had been isolated previously from tap water outlets in 8 out of 16 (50%) infection or colonization episodes. However, patients also harboured strains not previously isolated from tap water. Thus, in addition to tap water, other environmental or unknown reservoirs appeared to play a role for the epidemiology of P. aeruginosa infections on this ward. However, because tap water played a significant role for strain transmissions, we conclude that intensified water site care is justified.

Outbreak of long-term intravascular catheter-related bacteremia due to Achromobacter xylosoxidans subspecies xylosoxidans in a hemodialysis unit

Achromobacter xylosoxidans is a rare cause of bacteremia. Over a 2-week period, A. xylosoxidans subsp. xylosoxidans was isolated from blood cultures of four hemodialysis patients with long-term intravascular catheters. A culture from one atomizer that contained diluted 2.5% chlorhexidine, which had been used to disinfect the skin, yielded A. xylosoxidans subsp. xylosoxidans. No further cases were diagnosed once the use of this atomizer was discontinued. Five outbreak-related strains from the four patients and the atomizer were tested by pulsed-field gel electrophoresis (PFGE) under XbaI restriction. The isolates from the first three patients and the atomizer had identical PFGE patterns, confirming the atomizer as the source of the outbreak. The strain isolated from the fourth patient had six more bands than the outbreak strain and was considered possibly related to the outbreak strain. All patients were treated with intravenous levofloxacin. The catheter was removed in only one patient. The three patients in whom the catheter was left in place were also treated with antibiotic lock therapy with levofloxacin. All four patients were cured. This is believed to be the first reported outbreak of central venous catheter-related bacteremia due to A. xylosoxidans and the second reported outbreak with this organism associated with chlorhexidine atomizers. The use of diluted chlorhexidine via atomizers can be dangerous for the care of venous catheters and should be called into question. Patients with long-term intravascular catheter-related bacteremia due to this organism can be treated successfully with systemic antimicrobial therapy in addition to antibiotic lock therapy without catheter removal.

Ecology of Pseudomonas aeruginosa in the intensive care unit and the evolving role of water outlets as a reservoir of the organism

In spite of the significant changes in the spectrum of organisms causing intensive care unit (ICU)-associated infections, Pseudomonas aeruginosa has held a nearly unchanged position in the rank order of pathogens causing ICU-related infections during the last 4 decades. Horizontal transmissions between patients have long been considered the most frequent source of P aeruginosa colonizations/infections. The application of molecular typing methods made it possible, during the last approximately 7 years, to identify ICU tap water as a significant source of exogenous P aeruginosa isolates. A review of prospective studies published between 1998 and 2005 showed that between 9.7% and 68.1% of randomly taken tap water samples on different types of ICUs were positive for P aeruginosa , and between 14.2% and 50% of infection/colonization episodes in patients were due to genotypes found in ICU water. Faucets are easily accessible for preventive measures, and the installation of single-use filters on ICU water outlets appears to be an effective concept to reduce water-to-patient transmissions of this important nosocomial pathogen.

Microbial characterization of biofilms in domestic drains and the establishment of stable biofilm microcosms

We have used heterotrophic plate counts, together with live-dead direct staining and denaturing gradient gel electrophoresis (DGGE), to characterize the eubacterial communities that had formed as biofilms within domestic sink drain outlets. Laboratory microcosms of these environments were established using excised biofilms from two separate drain biofilm samples to inoculate constant-depth film fermentors (CDFFs). Drain biofilms harbored 9.8 to 11.3 log(10) cells of viable enteric species and pseudomonads/g, while CDFF-grown biofilms harbored 10.6 to 11.4 log(10) cells/g. Since live-dead direct staining revealed various efficiencies of recovery by culture, samples were analyzed by DGGE, utilizing primers specific for the V2-V3 region of eubacterial 16S rDNA. These analyses showed that the major PCR amplicons from in situ material were represented in the microcosms and maintained there over extended periods. Sequencing of amplicons resolved by DGGE revealed that the biofilms were dominated by a small number of genera, which were also isolated by culture. One drain sample harbored the protozoan Colpoda maupasi, together with rhabtidid nematodes and bdelloid rotifers. The microcosm enables the maintenance of stable drain-type bacterial communities and represents a useful tool for the modeling of this ecosystem.

Outbreak of severe Pseudomonas aeruginosa infections caused by a contaminated drain in a whirlpool bathtub

During a 14-month period, 7 patients with hematological malignancies acquired serious infections caused by a single strain of multiply resistant Pseudomonas aeruginosa. A case-control study, culture surveys, and pulsed-field gel electrophoresis implicated a whirlpool bathtub on the unit as the reservoir. All case patients and 32% of control patients used this bathtub (P=.003). The epidemic strain was found only in cultures of samples taken from the bathtub. The drain of the whirlpool bathtub, which was contaminated with the epidemic strain, closed approximately 2.54 cm below the drain's strainer. Water from the faucet, which was not contaminated, became contaminated with P. aeruginosa from the drain when the tub was filled. The design of the drain allowed the epidemic strain to be transmitted to immunocompromised patients who used the whirlpool bathtub. Such tubs are used in many hospitals, and they may be an unrecognized source of nosocomial infections. This potential source of infection could be eliminated by using whirlpool bathtubs with drains that seal at the top.

Molecular investigation of two clusters of hospital-acquired bacteraemia caused by multi-resistant Klebsiella pneumoniae using pulsed-field gel electrophoresis and in frequent restriction site PCR. Infection Control Group

Two molecular typing methods, DNA macrorestriction analysis with XbaI resolved by pulsed-field gel electrophoresis (PFGE) and infrequent restriction site PCR (IRS-PCR) assay with adapters designed for XbaI and HhaI restriction sites, were used to investigate two clusters of hospital-acquired bacteraemia associated with multi-resistant Klebsiella pneumoniae which occurred in a paediatric intensive care unit (PICU). A total of 56 K. pneumoniae isolates were analysed. These included 10 bacteraemic isolates from eight patients, 26 isolates obtained during an epidemiological survey, and 20 epidemiologically non-related isolates incorporated as controls. One major pattern was demonstrated in 22 of the 56 isolates analysed. These included nine of the 10 bacteraemic isolates, a single rectal isolate, two hand culture isolates and 10 sink isolates. All of these 22 isolates illustrated identical antibiograms, whilst the other 34 isolates shared six antibiograms and 31 unique patterns by either PFGE or IRS-PCR assay. The two clusters of bacteraemia appeared to be outbreaks induced by the same strain of K. pneumoniae which may have utilized sinks as reservoirs and been transmitted through the hands of medical personnel to patients. IRS-PCR demonstrates concordant results with PFGE analysis in studying the genetic relationships among K. pneumoniae isolates, and serves as an excellent epidemiological tool for this bacterium.

Eradication of a resistant Pseudomonas aeruginosa strain after a cluster of infections in a hematology/oncology unit

OBJECTIVES

This report chronicles an outbreak of a multiply resistant strain of Pseudomonas aeruginosa and the measures required to contain this outbreak.

METHODS

Laboratory-based ward-liaison surveillance allowed the detection of a multiply resistant strain of P. aeruginosa infecting patients in our hematology/oncology unit. Sampling of the immediate environment was carried out. Pulsed field gel electrophoresis was used to compare the patients' organisms with those found in the environment. Extensive dismantling of the drainage system, repeated cleaning and disinfection, and a review of the departmental antibiotic policy were some of the infection control measures instigated.

RESULTS

During a period of 11 months, three patients in the hematology department and two patients in the oncology department were infected with multiply resistant P. aeruginosa. There were two cases of pneumonia, one of which was fatal, and two cases of neutropenic septicaemia. Pulsed field gel electrophoresis performed on the isolates showed that the isolates from geographically separate areas could be divided into two strains that were closely related but distinct. Two genotypically identical strains were also isolated from the plumbing systems in the areas of each ward where patients had been treated.

CONCLUSIONS

The potential for serious nosocomial infections with P. aeruginosa is well recognized. Eradication of the organism from the environment may require the co-ordinated efforts of clinicians, nurses, pharmacy and hospital engineers, working in collaboration with the hospital infection control team. To date, the same strains have not been isolated despite repeated surveillance over the past 18 months and therefore these measures have, in our opinion, successfully removed the potential for nosocomial infection with this resistant organism in our hospital.

Topical antibiotics on tracheostoma prevents exogenous colonization and infection of lower airways in children

INTRODUCTION

Patients requiring long-term ventilation are at high risk of lower airway infections, generally of endogenous development. Patients on long-term ventilation, in particular via a tracheostomy, may develop tracheobronchitis or pneumonia of exogenous pathogenesis, ie, caused by microorganisms not carried in the oropharynx. The frequency of exogenous colonization or infection has previously been reported to be as high as 33%. A prospective observational cohort study of 2 years was undertaken to evaluate the efficacy of topical antibiotics in the prevention of exogenous colonization or infection of the lower airways. The antibiotic combination of polymyxin E and tobramycin in a 2% paste was applied four times a day on the tracheostoma.

MATERIALS AND METHODS

A total of 23 children (median age, 4.1 months; range, 0 to 215 months) were enrolled in the study from September 1, 1996, until August 30, 1998. Surveillance samples of the oropharynx were obtained before tracheostomy and thereafter twice weekly. Diagnostic samples of the lower airways were taken once weekly and on clinical indication.

RESULTS

Fourteen children (61%) had a total of 16 episodes of tracheal colonization or infection with 20 potentially pathogenic microorganisms. Only one child had tracheobronchitis with Streptococcus pneumoniae and Haemophilus influenzae during the 2-year study. Of the 16 colonization episodes, 12 (75%) were of primary endogenous pathogenesis, ie, caused by microorganisms present in the oropharynx at the time of tracheostomy. Community microorganisms including S pneumoniae, H influenzae, Moraxella (Branhamella) catarrhalis, and Staphylococcus aureus were the predominating bacteria. Three patients acquired nosocomial bacteria Pseudomonas aeruginosa and Hafnia alvei in the oropharynx, subsequently followed by secondary colonization of the lower airways. There was one failure of the prophylaxis: one patient (4%) had exogenous colonization with Pseudomonas pickettii.

CONCLUSION

Topical antibiotics applied to the tracheostoma were found to be effective in reducing the exogenous route of colonization of the lower respiratory tract, compared with clinical experience and the literature. This promising technique requires further evaluation in randomized trials.

Mopping up hospital infection

Hospital cleaning is a neglected component of infection control. In the UK, financial constraints have forced managers to re-evaluate domestic services and general cleaning has been reduced to the bare minimum. Services have been contracted out in some hospitals, which has further lowered standards of hygiene. Control of infection personnel believe that cleaning is important in preventing hospital-acquired infections but they do not manage domestic budgets and have failed to stop their erosion. It is difficult to defend high levels of hygiene when there is little scientific evidence to support cleaning practices. This review examines the common micro-organisms associated with hospital-acquired infection and their ability to survive in the hospital environment. It also describes studies which suggest that comprehensive cleaning disrupts the chain of infection between these organisms and patients. It is likely that restoring hygienic standards in hospitals would be a cost-effective method of controlling hospital-acquired infection. Furthermore, good cleaning is achievable whereas the enforcement of hand washing and good antibiotic prescribing are not.

Multiresistant Pseudomonas aeruginosa outbreak in a pediatric oncology ward related to bath toys

BACKGROUND

Nosocomial outbreaks of Pseudomonas aeruginosa in pediatric hospitals frequently involve neonates and immunosuppressed patients and can cause significant morbidity and mortality.

OBJECTIVE

To describe the investigation of a multidrug-resistant P. aeruginosa outbreak in a pediatric oncology ward at the Royal Children's Hospital, Melbourne, Australia.

DESIGN AND METHODS

Specimens were collected from infected patients and the ward environment. Bacterial isolates were characterized by antibiotic susceptibility patterns and bacterial DNA fingerprinting performed by pulsed-field gel electrophoresis (PFGE). A case-control study was carried out to assess possible risk factors for infection.

RESULTS

Eight patients had clinical illnesses including bacteremia (n = 5) and infections of skin (n = 2), central venous catheter site (n = 1) and urinary tract (n = 1). The environmental ward survey yielded isolates of multiresistant P. aeruginosa from a toy box containing water-retaining bath toys, as well as from three of these toys. Pulsed-field gel electrophoresis of bacterial DNA demonstrated identical band patterns of the isolates from patients, toys and toy box water. A case-control study involving the 8 cases and 24 disease-matched controls demonstrated a significant association between P. aeruginosa infection and use of bath toys (P = 0.004), use of bubble bath (P = 0.014), duration of stay (P = 0.007) and previous antibiotic exposure (P = 0.026). Cultures from the bubble bath liquid were negative.

CONCLUSION

This is the first description of a nosocomial outbreak associated with toys. We caution against the use of water-retaining bath toys in wards treating immunocompromised children.

Outbreak of gram-negative septicaemia caused by contaminated continuous infusions prepared in a non-clinical area

An outbreak of Gram-negative septicaemia due to cross infection on an acute cardiology ward is reported. This outbreak was facilitated by two factors: first, an area originally designed for non-clinical purposes was converted into a clean utility area without consulting the infection control team, and second, changes in staff had taken place at the same time. This outbreak emphasizes the importance of continuous staff training in infection control, the involvement of the infection control team in all building alterations and the need to improve recommendations by the Department of Health in the design of clean utility areas.

Comparative hygienic surveillance of contamination with pseudomonads in a cystic fibrosis ward over a 4-year period

In order to study the long-term distribution and population dynamics of Pseudomonas aeruginosa strains in a highly contaminated hospital environment, two 4-week epidemiological studies, with an interval of 4 years, were carried out in the cystic fibrosis (CF) ward of the Paediatric Clinic of the Medical School of Hannover. Out of the 1948 specimens taken, P. aeruginosa was mainly identified in those from moist, inanimate sources (200 isolates) and hospitalized CF patients (168 isolates). A correlation was established between the frequency with which P. aeruginosa-positive patients came into contact with hospital facilities and the rate of contamination of these facilities. Rooms reserved for colonized patients were more frequently contaminated with P. aeruginosa in contrast to function rooms in the same ward and the outpatient clinic. However, no direct exchange between patients' strains and the inanimate hospital environment was detected. Out of the 11 genotypes of P. aeruginosa found in 1989 and the 13 genotypes found in 1993, four genotypes were present on both occasions. The most predominant clone was found in tap-water, sinks, wash-basins and creams with an incidence of 34 and 68% in the environmental isolates. The strains seemed to have spread into the adjacent control ward during the 4-year interval. Thus, the separation of colonized and non-colonized patients was undermined through the transfer of strains from a highly contaminated environment without additional hygiene precautions.

Antibiotic-resistant gram-negative bacteria in the critical care setting

Gram-negative bacilli that are resistant to commonly used antibiotics are a growing problem in seriously ill, hospitalized patients. Numerous outbreaks involving these organisms have been reported in intensive care nurseries and among critically ill adults. In endemic situations, the major reservoir for these pathogens is the patient; occasionally, transmission from patient to patient occurs through the hands of caregivers. Although the degree of antibiotic use probably plays some role in the emergence of antibiotic-resistant gram-negative bacilli, this relationship has not been uniformly demonstrated, and other factors intrinsic to the organisms themselves and to the critically ill patient may play an important role.

Outbreak of gentamicin, ciprofloxacin-resistant Pseudomonas aeruginosa in an intensive care unit, traced to contaminated quivers

An outbreak of gentamicin, ciprofloxacin-resistant Pseudomonas aeruginosa in an intensive care unit, was investigated. The majority of isolates were from sputum and the organism was not isolated from any other patient in the hospital, except those admitted to the unit. A prospective study was set up, and the organism was found to be associated with contaminated quivers, used to store suction tubing between use on ventilated patients. Once the quivers were disinfected and changed between patients daily, the outbreak stopped. Suction of ventilated patients may be an important source of contamination of the respiratory tract with nosocomial pathogens. It is important that infection control teams regularly review procedures to ensure the correct practices are being followed, so that nosocomial outbreaks of infection may be prevented.

Lack of association between clinical and environmental isolates of Pseudomonas aeruginosa in hospital wards

Seventy-three environmental and clinical isolates of Pseudomonas aeruginosa recovered from a single hospital over a 6-month period were compared for epidemiological type characteristics. Environmental isolates were obtained from sinks, taps and water, in rooms where patients were treated. The strains represented only six O-antigenic types and 8.2% of them were not typable. Serotype 011 was most frequent in the environment, whereas serotypes 06, 012 and 02,5 predominated among clinical isolates. More than 60% of all isolates belonged to four pyocin types (1, 10, 33 and 45), and approximately 80% were phage typable. Environmental isolates were more sensitive to antibiotics than clinical isolates. There was little correspondence between the types of strains of P. aeruginosa isolated from patients and those isolated from the environment. However, isolates of identical type were frequently recovered from different patients within the same clinic and were found to be related in time and location. We conclude that the environment was not an important source of P. aeruginosa infection and that transfer of organisms was mainly from patient-to-patient.

Molecular epidemiology of Pseudomonas aeruginosa in an intensive care unit

Genotyping was used to analyse Pseudomonas aeruginosa isolates from sink drains and 15 intubated patients as part of a 3-month prospective study of strain transmission in a medical-surgical intensive care unit. Ninety percent of all washbasin drains were persistently contaminated with several P. aeruginosa genotypes. In 60% (9/15) of the patients, P. aeruginosa colonization or infection was hospital-acquired: P. aeruginosa strains isolated from these patients were present in hospital sinks or in other patients before their admission. Since all patients were immobile, personnel were the probable route of transmission of P. aeruginosa in the hospital. The mechanism of strain transmission from sinks to hands during hand washing was investigated in a children's hospital. When P. aeruginosa was present at densities of > 10(5)/c.f.u. per ml in sink drains, hand washing resulted in hand contamination with P. aeruginosa via aerosol generation in the majority of experiments or P. aeruginosa was detected using an air sampler above the washing basin. High P. aeruginosa cfu were present at 4.30 h in the eight sinks (5.4 x 10(5)-7.0 x 10(10) c.f.u./ml), whereas at 13.00 h P. aeruginosa c.f.u. were significantly lower (3.1 x 10(2)-8.0 x 10(5) c.f.u./ml). These data reveal that the danger of bacterial contamination of hands during hand washing is highest in the morning. The identified transmission routes demand more effective hygienic measures in hospital settings particularly concerning personnel hands and sink drains.

Exogenous or endogenous reservoirs of nosocomial Pseudomonas aeruginosa and Staphylococcus aureus infections in a surgical intensive care unit

OBJECTIVE

A 4 month prospective study was performed to assess the incidence and routes of endogenous or exogenous colonization and nosocomial infection caused by Staphylococcus aureus and Pseudomonas aeruginosa in surgical critically ill patients.

DESIGN

A total of 4634 specimens were obtained. Patient's nasal, scalp, and rectal swabs as well as tracheal secretion (TS) were cultured every second day beginning on the day of admission. Nasal swabs and hand cultures of the personnel as well as cultures from gowns were also taken. All isolates of S. aureus were phage typed and 116 of these isolates were also plasmid typed. P. aeruginosa isolates were sero- and pyocin typed. Resistance patterns were determined in all isolates.

SETTING

The study was carried out in the surgical intensive care unit (SICU) of an teaching hospital.

PATIENTS

During the study period each patient (a total of 153 patients) admitted to the SICU entered the study.

RESULTS

P. aeruginosa and S. aureus colonisation rate on admission were 5% and 36.5% respectively. Only 10 patients (6.5%) were colonized with P. aeruginosa during hospitalization, and only 7 patients (4.5%) acquired S. aureus in the surgical intensive care unit (SICU). The most common primary colonisation site of P. aeruginosa was the rectum, whereas S. aureus was predominantly found in nasal cultures. Horizontal transmission of S. aureus occurred in only 2 patients.

CONCLUSION

The study suggests that colonisation with P. aeruginosa and S. aureus occurs from endogenous rather than from exogenous sources and that the endogenous acquisition of both bacteria play a more important role in development of nosocomial infections than the exogenous route of transmission.

Investigation of an outbreak of nosocomial infection due to a multiply drug-resistant strain of Pseudomonas aeruginosa

A nosocomial outbreak of Pseudomonas aeruginosa infections which occurred in the Urology Service of a large city hospital was studied. A case-control methodology was used to analyse patients' characteristics and the main risk factors of all cases with a positive culture during the period between March 1987 and March 1988. The usefulness of factor analysis in the definition of a case was examined. There were 74 infections of which 35 (47.3%), had a nosocomial origin. The outbreak took place in December 1987, with a peak incidence of infections of 10.5%, compared with a 2.2% frequency during the preceding months (P less than 0.005). Six of the nine infections occurring in that month, were caused by strains resistant to ticarcillin and gentamicin. The epidemic cases had longer hospital stays than the non-epidemic cases (P less than 0.038) and occurred more frequently in a specific area of the hospital (P less than 0.001). The odds ratio for resistance to gentamicin was 15 (P less than 0.018) and that of resistance to ticarcillin, 127 (P less than 0.0001). Our results suggest that inaccurate case definitions may produce misleading conclusions. Factor analysis appears to be a useful analytical tool when defining a case.

Epidemiology and control of nosocomial infections in adult intensive care units

Traditional infection control measures in intensive care units (ICUs) have been directed at limiting person to person spread of infection and improving care of invasive devices. These measures often fail because they have little effect on patients' endogenous flora, which is an important source of infection in ICUs. Improvements in the design and aseptic care of invasive devices have helped to decrease the risk of progression from colonization to infection in individual patients. Interest is growing also in use of selective decontamination to decrease ICU infection rates. Despite these advances, basic hygiene and appropriate, prospectively monitored use of antibiotics remain essential components of ICU care.

Sink flora in a long-stay hospital is determined by the patients' oral and rectal flora

Sinks in a new long-stay hospital (LSH) were cultured weekly during 4 consecutive months to evaluate the microbial profile before and after occupancy of the hospital. From the elderly patients admitted to the patient care rooms oral and rectal specimens were collected to examine the contribution of the patients' flora to the sink contamination. Isolates were typed biochemically, serologically and by susceptibility pattern. Before occupancy Gram-negative bacilli were not isolated. Once the elderly patients, who were highly colonized on admission, occupied their rooms identical strains gradually contaminated the sinks. Escherichia coli, Klebsiella, Pseudomonas and Acinetobacter species were the major correlating strains. The mean concentration of the correlating isolates was higher in throat and intestines compared to the mean concentration of the non-correlating strains. These strains seem to have a greater chance to be shed and then transferred via the hands of personnel to sinks. This report shows that the major route of environmental contamination is from patient carriers to sinks, and not the reverse way.

Gastrointestinal colonization and septicaemia with Pseudomonas aeruginosa due to contaminated thymol mouthwash in immunocompromised patients

An outbreak of septicaemia with Pseudomonas aeruginosa amongst adult men with haematological malignancy involved eight patients on the same ward during a period of 5 weeks. The strains isolated from blood cultures from seven patients were indistinguishable by conventional typing methods. Thymol mouthwash which had been made up and distributed in communal jugs was found to be contaminated with the epidemic strain and was the likely source for this outbreak. A high rate of gastrointestinal colonization with the epidemic strain was found in the patients receiving the contaminated mouthwash. Only those patients with prolonged severe leucopenia developed septicaemia. Communal medications are an unnecessary hazard, particularly in oncology wards.