Pseudomonas aeruginosa cross-infection due to contaminated respiratory apparatus

Epidemiology of Pseudomonas aeruginosa in agricultural areas. J Med Microbiol 2018;67:1191-1201. [PMID: 30067169 DOI: 10.1099/jmm.0.000758]

A prevailing opinion is that the strains of Pseudomonas aeruginosa that infects both plants and humans are two separate species. This study strongly disputes that notion until the modern molecular technology proves otherwise. This paper examines a spectrum of strains occurring in nature, their habitats, dissemination, their relationship to clinical strains, and the environmental conditions that favor their colonization of plants. The isolates were obtained from clinical specimens, plants, soil, and water. The identity of these strains was confirmed using pyocin typing and biochemical assays. The data reveal that agricultural soils, potted ornamental plants, hoses, fountains, and faucets frequently harbored P. aeruginosa. However, it was not commonly found in semi-arid areas, suggesting that moisture and high humidity is necessary for colonization and survival. Though found in soil, P. aeruginosa was seldom isolated on edible plant parts. The pathogenicity of various strains on plants was tested by inoculating vegetables, lettuce slices (Lactuca sativa L. "Great Lakes"), celery stalks (Apium graveolens L. var. Dulce], potato tuber slices (Solanum tuberosum L. "Whiterose"), tomato (Lycopersicon esculentum L. Mill), cucumber (Cucumis sativus L.), rutabaga (Brassica campestris L.), and carrot (Daucus carota L. var sativa). There was considerable variation in the strains' ability to cause rot, but no difference was observed between clinical isolates and others from agricultural fields, water, and soil. Two of the clinical isolates from burn patients, P. aeruginosa PA13 and PA14, exhibited the greatest virulence in causing rot in all the plants that were tested, especially on cucumber, lettuce, potato, and tomato. The study discusses how closely the epidemiology of P. aeruginosa relates to many plant pathogens, and the ability of human isolates to colonize plants and food material under favorable conditions. The biochemical and phenotypic similarity among strains from the clinical and agricultural material is strongly indicative that they are the same species and that plants and soil are natural reservoirs for P. aeruginosa.

Bacterial and viral contamination of breathing circuits after extended use - an aspect of patient safety?

BACKGROUND

In the past, anaesthetic breathing circuits were identified as a source of pathogen transmission. It is still debated, whether breathing circuits combined with breathing system filters can be safely used for more than 1 day. The aim of this study was to evaluate the transmission risk of bacteria and also viruses via breathing circuits after extended use.

METHODS

The inner and outer surface of 102 breathing circuits used for 1 day and of 101 circuits used for 7 days were examined for bacteria and viruses. Additionally, 10 and 20 breathing circuits each were examined after use on patients with pulmonary virus infection and with multidrug-resistant organism (MDRO) colonisation/infection respectively. Bacteria were detected by standard microbiological procedures; PCR techniques were applied for herpes simplex virus, cytomegalovirus, influenza, parainfluenza and respiratory syncytial virus.

RESULTS

Endoluminal bacterial contamination of breathing circuits remained unchanged after 7-day vs. 1-day use (5.9% vs. 7.8%) [CI95%: -0.0886-0.0506, pnon-inferiority 0.0260]. Only outside surface contamination with bacteria belonging to environmental species or human flora increased (16.8 vs. 6.9%) [CI 95%: 0.0118 - 0.1876, pnon-inferiority 0.8660]. Viruses occurred on the patient side, but not in breathing circuits. No MDRO occurred in the 20 circuits after use on patients harbouring such germs.

CONCLUSION

Endoluminal contamination of breathing circuits with bacteria did not increase after extended use. No viruses were detected in the breathing circuits using filters. Based on our results, the extended use of ABC without exceptions appears safe, if a high level of anaesthesia workplace cleaning is secured.

Periodically Changing Ventilator Circuits Is Not Necessary to Prevent Ventilator-Associated Pneumonia When a Heat and Moisture Exchanger Is Used

Objective:

To analyze the efficacy of periodically changing ventilator circuits for decreasing the rate of ventilator-associated pneumonia when a heat and moisture exchanger (HME) is used for humidification. The Centers for Disease Control and Prevention recommended not changing the circuits periodically.

Design:

Randomized, controlled trial conducted between April 2001 and August 2002.

Setting:

A 24-bed, medical–surgical intensive care unit in a 650-bed, tertiary-care hospital.

Patients:

All patients requiring mechanical ventilation during more than 72 hours from April 2001 to August 2002.

Interventions:

Patients were randomized into two groups: (1) ventilation with change of ventilator circuits every 48 hours and (2) ventilation with no change of circuits. Throat swabs were taken on admission and twice weekly until discharge to classify pneumonia as endogenous or exogenous.

Results:

Three hundred four patients (143 from group 1 and 161 from group 2) with similar characteristics (age, gender, Acute Physiology and Chronic Health Evaluation II score, diagnostic group, and mortality) were analyzed. There was no significant difference in the rate of pneumonia between the groups (23.1% vs 23.0% and 15.5 vs 14.8 per 1,000 ventilator-days). There was no significant difference in the incidence of exogenous pneumonia per 1,000 days of mechanical ventilation (1.71 vs 1.25). There was no difference in the distribution of microorganisms causing pneumonia.

Conclusions:

Circuit change using an HME for humidification does not decrease pneumonia and represents an unnecessary cost.

The microbial colonization profile of respiratory devices and the significance of the role of disinfection: a blinded study

INTRODUCTION

Approximately 10-40% of all the nosocomial infections are pulmonary, which lead to grave complications. Elderly, debilitated, or critically ill patients are at a high risk. The respiratory care equipments which include ventilators, humidifiers, nebulizers may have been identified as the potential vehicles which cause major nosocomial infections if they are colonized by fungi or bacteria.

AIM

To determine the rate of colonization by bacteria and fungi of the oxygen humidifier chambers of the portable cylinders and central lines at our hospital. The Hudson's chambers of nebulizers were also studied for the same.

METHODS

Swab samples were obtained from the equipments by using sterile cotton swabs on a tuesday, as these chambers were usually cleaned on every Saturday. Spot samples were taken from the ICUs, wards, the casualty and OPDs on a single day. Air samples were also obtained on the same day to determine whether the fungal spore load in the inhaled room air was normal or high. We performed a disinfection with 70% ethanol after cleaning these devices.

RESULTS

53/70 (75.71%) samples showed fungal growth; out of which, 23/33 (69.70%) were from the ICU, 24/30(80%) were from the wards and 6/7 (85.71%) were from the OPDs. 23/30 (76.66%) swabs from the central line humidifiers, 18/23(78.26%) swabs from the O2 cylinder humidifiers and 8/17 (47.5%) swabs from the nebulizers grew bacteria. Of the total 61(87.14%) bacterial isolates, 42(68.85%) were gram negative bacteria and 19(31.14%) were gram positive cocci. Out of the 42 gram negative bacteria, 17 were multi-drug resistant like ESBL producers ie. Pseudomonas spp. (6) Acinetobacter spp.(4), Klebseilla pneumoniae (4), E.coli (2) and Stenotrophomonas maltophila (1). Our findings (before disinfection) showed that the colonization rate for fungi was 75% and that for bacteria, it was 87%. After the 70% ethanol disinfection and strict compliance with the hand hygiene, the colonization rates reduced significantly. The fungal colonization rate was reduced and only 15% fungi grew after the disinfection, while only 12% bacterial colonization rate was found.

CONCLUSION

This study indicates a potential in-hospital source of allergens and infections. The oxygen and nebulizer chambers need to be cleaned more frequently with disinfectants, to control the possible nosocomial infections.

[Prevention of infections under anesthetic breathing with breathing filters: concerted recommendations of the Deutsche Gesellschaft für Krankenhaushygiene e.V. (DGKH) and the Deutsche Gesellschaft für Anästhesiologie und Intensivmedizin e.V. (DGAI)]

An interdisciplinary working group from the German Society of Hospital Hygiene (DGKH) and the German Society for Anesthesiology and Intensive Care (DGAI) worked out the following recommendations for infection prevention during anesthesia by using breathing system filters (BSF). The BSF shall be changed after each patient. The filter retention efficiency for airborne particles is recommended to be >99% (II). The retention performance of BSF for liquids is recommended to be at pressures of at least 60 hPa (=60 mbar) or 20 hPa above the selected maximum ventilation pressure in the anesthetic system.The anesthesia breathing system may be used for a period of up to 7 days provided that the functional requirements of the system remain unchanged and the manufacturer states this in the instructions for use. The breathing system and the manual ventilation bag are changed immediately after the respective anesthesia if the following situation has occurred or it is suspected to have occurred: Notifiable infectious disease involving the risk of transmission via the breathing system and the manual bag, e.g. tuberculosis, acute viral hepatitis, measles, influenza virus, infection and/or colonization with a multi-resistant pathogen or upper or lower respiratory tract infections. In case of visible contamination e.g. by blood or in case of defect, it is required that the BSF and also the anesthesia breathing system is changed and the breathing gas conducting parts of the anesthesia ventilator are hygienically reprocessed.Observing of the appropriate hand disinfection is very important. All surfaces of the anesthesia equipment exposed to hand contact must be disinfected after each case.

Heat and moisture exchangers and breathing system filters: their use in anaesthesia and intensive care. Part 1 - history, principles and efficiency

Heat and moisture exchangers and breathing system filters are intended to replace the normal warming, humidifying and filtering functions of the upper airways when these structures are bypassed during anaesthesia and intensive care. Guidance on their use continues to evolve. The aim of this part of the review is to describe the principles of their action and efficiency and to summarise the findings from clinical and laboratory studies. Based on previous studies, an appropriate minimum target for moisture output is 30 and 20 g.m⁻³ for long-duration use in intensive care and short-duration use in anaesthesia, respectively. The practice of reusing a breathing system in anaesthesia, provided it is protected by a filter, assumes that the filter is effective. However, there is wide variation in the gas-borne filtration performance, and contaminated condensate can potentially pass through some filters under typical pressures encountered during mechanical ventilation.

Infection prevention during anaesthesia ventilation by the use of breathing system filters (BSF): Joint recommendation by German Society of Hospital Hygiene (DGKH) and German Society for Anaesthesiology and Intensive Care (DGAI)

An interdisciplinary working group from the German Society of Hospital Hygiene (DGKH) and the German Society for Anaesthesiology and Intensive Care (DGAI) worked out the following recommendations for infection prevention during anaesthesia by using breathing system filters (BSF). The BSF shall be changed after each patient. The filter retention efficiency for airborne particles is recommended to be >99% (II). The retention performance of BSF for liquids is recommended to be at pressures of at least 60 hPa (=60 mbar) or 20 hPa above the selected maximum ventilation pressure in the anaesthetic system. The anaesthesia breathing system may be used for a period of up to 7 days provided that the functional requirements of the system remain unchanged and the manufacturer states this in the instructions for use.THE BREATHING SYSTEM AND THE MANUAL VENTILATION BAG ARE CHANGED IMMEDIATELY AFTER THE RESPECTIVE ANAESTHESIA IF THE FOLLOWING SITUATION HAS OCCURRED OR IT IS SUSPECTED TO HAVE OCCURRED: Notifiable infectious disease involving the risk of transmission via the breathing system and the manual bag, e.g. tuberculosis, acute viral hepatitis, measles, influenza virus, infection and/or colonisation with a multi-resistant pathogen or upper or lower respiratory tract infections. In case of visible contamination e.g. by blood or in case of defect, it is required that the BSF and also the anaesthesia breathing system is changed and the breathing gas conducting parts of the anaesthesia ventilator are hygienically reprocessed.Observing of the appropriate hand disinfection is very important. All surfaces of the anaesthesia equipment exposed to hand contact must be disinfected after each case.

Pseudomonas aeruginosa respiratory tract infections in patients receiving mechanical ventilation

Eighteen patients treated by tracheostomy and mechanical ventilation were studied in an attempt to determine whether contaminated ventilators could act as a source ofPseudomonas aeruginosaisolated from the respiratory tract. Twelve became infected. In seven instances it was possible to demonstrate prior contamination of the ventilator. Furthermore, eight of the patients had indistinguishable organisms on the basis of pyocine and phage typing, and six of the ventilators harboured the same organisms. The most likely explanation is cross-infection via contaminated machines.

An investigation of the bacterial contamination of small animal breathing systems during routine use

OBJECTIVE

To investigate the need for sterilization of anaesthetic breathing systems to prevent cross-infection between animals due to the re-use of anaesthetic circuit tubing.

STUDY DESIGN

Prospective microbiological study.

METHODS

Bacteriology samples were taken from 37 sterile breathing systems, each used for 1 day, at two sampling sites (one proximal and one distal to the animal). The number of patient connections, cumulative anaesthesia time, culture results, number of colony-forming units and the number of different species were recorded. Secondly, four sterile breathing systems were used for 2 months under routine conditions and sampled every 2 weeks and the same parameters recorded. Finally, the inner surfaces of four sterile breathing systems were inoculated with a known load of canine oropharyngeal bacteria. Bacteriology samples were taken at 1 minute, 1 hour and 1 day post-deposition. The number of colonies identified was compared with the initial load.

RESULTS

Only a very small number of micro-organisms were isolated and these were generally organisms of low pathogenic potential. The proximal site was found to be significantly more colonized than the distal site (p < 0.001). Neither longer daily connection time (p = 0.54), nor a higher number of connections (p = 0.81) increased the incidence of proximal site colonization. Over the 2-month study period, the bacterial population did not increase. There was no correlation between cultures isolated from successive samples taken from the same tubing. There was rapid loss of viability of the micro-organisms deliberately inoculated onto the tubing surface: the number of colonies isolated from the breathing system after 1 minute was significantly lower than in the inoculum (p = 0.042).

CONCLUSIONS AND CLINICAL RELEVANCE

Sterile anaesthesia breathing systems were colonized by environmental micro-organisms of low pathogenicity. Although long-term survival of recognized pathogens in a dry environment is still possible, the use of a bacterial filter or a sterilized breathing system for routine veterinary anaesthesia cannot be supported by current evidence.

Filters in anaesthesia and intensive care

The use of various types of filters in anaesthesia and intensive care seems ubiquitous, yet authentication of the practice is scarce and controversies abound. This review examines evidence for the practice of using filters with blood and blood product transfusion (standard blood filter, microfilter, leucocyte depletion filter), infusion of fluids, breathing systems, epidural catheters, and at less common sites such as with Entonox inhalation in non-intubated patients, forced air convection warmers, and air-conditioning systems. For most filters, the literature failed to support routine usage, despite this seemingly being popular and innocuous. The controversies, as well as guidelines if available, for each type of filter, are discussed. The review aims to rationalize the place of various filters in the anaesthesia and intensive care environment.

The bacterial and viral filtration performance of breathing system filters

The bacterial and viral filtration performance of 12 breathing system filters was determined using test methods specified in the draft European standard for breathing system filters, BS EN 13328-1. All the filters were of two types, either pleated hydrophobic or electrostatic, and these two types differed in their filtration performance. The filtration performance is expressed in terms of the microbial penetration value, defined as the number of microbes passing through the filter per 10 million microbes in the challenge. The geometric mean (95% confidence limits) microbial penetration value was 1.0 (0.5, 3.5) and 2390 (617, 10 000) for the pleated hydrophobic and electrostatic filters, respectively, for the bacterial challenge, and 87 (48, 212) and 32 600 (10 900, 84 900), respectively, for the viral challenge. In general, there was little change in the microbial penetration values following 24 h simulated use. It is concluded that results from the tests specified in the draft standard will allow comparisons to be made between different manufacturers' products enabling an informed choice to be made.

Efficacy of a washer-pasteurizer for disinfection of respiratory-care equipment

We evaluated the efficacy of a commercial washer-pasteurizer. Carriers were inoculated with 10(4) to 10(6) test organisms and pasteurized at 170 degrees F for 30 minutes. Pasteurization eliminated all test organisms with the exception of Bacillus subtilis spores. Pasteurization appears efficacious for the disinfection of respiratory-care equipment and could result in a cost savings of approximately $30,000 per year.

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.

History of infection control in anaesthesia

Generally the basic sciences of physics, chemistry and mathematics and the applied sciences of anatomy physiology and pharmacology are associated with the history of the development and advancement of anaesthesia. In considering the history of infection control in anaesthesia, the contribution of microbiology must be added to the above. When sifting through old books and journals it is often difficult to understand the stimuli for the leaps of progress; I believe the zeitgeist is often the invisible (to our eyes) all important factor. An attempt to briefly illustrate some of the main events and characters follows.

Anaesthetic machine and breathing system contamination and the efficacy of bacterial/viral filters

Contamination of the anaesthetic machine and breathing system by the environment and by patient exposure has been shown to occur. Outside the intensive care setting, however, it is difficult to demonstrate that the anaesthetic machine and breathing system are a vector for patient cross-infection. Bacterial and viral filters for use within the breathing system have been shown to be very effective for filtration, yet their use has not been demonstrated to be of benefit in the prevention of cross-infection between patients. Several instances of patient morbidity are a direct consequence of filter use. The use of bacterial/viral filters may represent another step towards defensive medical practice.

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.

Bacterial and viral removal efficiency, heat and moisture exchange properties of four filtration devices

Four devices used for filtration of microorganisms and/or for heating and moistening the ventilated air during mechanical ventilation were evaluated. This evaluation included measurement of bacterial and viral removal efficiency, heat and moisture exchange properties, dead space and air flow resistance. The devices included: Pall BB50T and DAR Sterivent (filtration devices); DAR Hygrobac and Gibeck Humid-vent [heat and moisture exchangers (HMEs)]. The two devices which are primarily conceived as filters, had the highest bacterial and viral removal efficiency (titre reduction of 10(5)-10(6) for bacteria and of 10(4)-10(5) for viruses), while removal efficiencies of the HME devices were lower: titre reduction of 10(4) for bacteria and 10(1)-10(3) for viruses. As expected, heat and moisture output of HMEs was better than that of filters. In mechanical ventilation, dead space and air flow resistance are important properties of devices, which might disturb efficient ventilation. There were only minor differences in dead space and air flow resistance. Resistance to airflow in the HMEs was increased by nebulization of medication (mesna) unlike that of the filters.

Colonization of intensive care unit patients by Pseudomonas aeruginosa

Colonization and infection by Pseudomonas aeruginosa was found at several sites by selective culture in 32 of 66 patients in an intensive care unit. Twenty-four patients (75%) were colonized on admission, and eight patients (25%) acquired P. aeruginosa during hospitalization. Positive rectal cultures were more frequent than at any other site. The most common P. aeruginosa serotypes were 1, 2, 3 and 5, and pyocin types 1, 3, 5 and 10 were predominant. There were no significant differences in the serotypes or pyocin types detected on admission or acquired during hospitalization. The serotypes and pyocin types from the respiratory tract (trachea and nasopharynx) were different from those found in the rectum. Intubated patients were colonized more frequently than those not intubated and upper respiratory tract colonization correlated strongly with low initial arterial pH values.

Bacterial filters protect anaesthetic equipment in a low-flow system

We have recently described a low-flow system with mechanical ventilation in which there was an open connection between the circle and ventilator. In the present study bacterial contamination and the role of bacterial filters at different points in the system were studied. Filters between the tracheal tube and circle are an effective barrier, but their absence did not increase contamination of either the circle or the ventilator. Some filters are also effective as heat and moisture exchangers if situated at the tracheal tube. Because of the lack of bacterial contamination, a prolonged interval between disinfection of the open connection and ventilator is acceptable, which reduces wear and costs.

Bacterial contamination and the effect of filters in anaesthetic circuits in a simulated patient model

In order to investigate bacterial contamination of anaesthetic breathing circuits and means of prevention of this, six different laboratory experiments were performed. These experiments involved the bacterial contamination of Dräger Narkose Spiromat 650 and Dräger AV-1 circle system circuits and of an isolated soda lime carbon dioxide absorber. The effects of anaesthetic gas, gas flow rate and the incorporation of a hydrophobic membrane heat and moisture exchanging bacterial/viral filter (HMEF) at the patient end of these circuits were investigated. It was found that without a HMEF the whole interior of the anaesthetic circuits became contaminated with bacteria. Components closest to the simulated patient showed the highest levels of contamination. Higher gas flows were associated with decreased levels of circuit contamination, presumably because more bacteria were expelled from the system. Halothane (1 volume %) and soda lime were not found to have any demonstrable bactericidal action. The presence of a HMEF between the simulated patient and the Y-piece prevented any detectable contamination from reaching the circuit. Consequently, the presence of a HMEF provides protection of the anaesthetic circuit as well as other patients, healthcare workers and the environment.

Bacterial colonisation of humidifier attachments on oxygen concentrators prescribed for long term oxygen therapy: a district review

A microbiological survey was undertaken on the eight patients in the Liverpool District who have a humidifier attachment on their oxygen concentrator. All but one of the humidifiers were contaminated with potentially pathogenic bacteria.

Contamination control in long-term ventilation. A clinical study using a heat- and moisture-exchanging filter

Twenty-eight patients who required periods of mechanical ventilation for up to 22 days in the intensive therapy unit were studied to evaluate the clinical use of the Pall Ultipor Breathing System Filter (BB50T) as a heat- and moisture-exchanging bacterial filter. Results in this group of patients showed that there was no longer any need to sterilise breathing systems or decontaminate ventilators if these filters were used. They also performed satisfactorily as a heat and moisture exchanger in patients in need of long-term ventilation, and their use appears to offer substantial advantages as regards cost, ease of use and patient safety.

Bacterial contamination of ambulance oxygen humidifier water reservoirs: a potential source of pulmonary infection

The risk and benefit of oxygen humidification during ambulance transport is unknown. We cultured the water in plastic multiple-use bottles of humidifiers on 30 randomly selected area ambulances during November 1985. There were 22 positive cultures. Potentially pathogenic bacteria (four Pseudomonas maltophilia, three Pseudomonas aeruginosa, one Klebsiella pneumoniae, and one Staphylococcus epidermidis) were found in nine samples. Assuming that the water in ambulance humidifiers should have been sterile, the findings are statistically significant (P less than .01). Because there is no evidence that humidification is of benefit for nonintubated patients receiving oxygen at flow rates of 4 L/min or less when environmental humidity is adequate, we suggest that such patients should receive oxygen without humidification during ambulance transport. All other patients requiring oxygen during ambulance transport should continue to receive humidified oxygen. If a multiple-use humidifier reservoir is to be used, a written policy for its use must be developed and there must be appropriate documentation of compliance with the policy. An alternative is to replace the multiple-use humidifier reservoir with single-use sterile disposable devices, which cost approximately $2.00 per unit.

The colonization of patients in an intensive treatment unit with gram-negative flora: the significance of the oral route

An extensive survey of patients and the environment in a newly refurbished intensive care unit showed that the principle species on patients in sites other than the rectum were Pseudomonas aeruginosa, Klebsiella pneumoniae, Serratia marcescens, Acinetobacter anitratus and Enterobacter cloacae. Multiple episodes of cross-infection were occurring with 10 different strains of these organisms. Three oral solutions (mouthwashes, 'Clinifeeds' and residual water from nasogastric aspiration apparatus) were heavily contaminated with coliforms including some epidemic strains and this corresponded with the finding that colonization with the above species usually occurred first in the mouth or respiratory tract. Attempts to eliminate contamination of the solutions reduced colonization and cross-infection by over 50%, but did not eradicate it. Two sinks without heat-traps on the drains possibly provided a long term reservoir of epidemic strains.

Pseudomonas aeruginosa colonisation in an intensive therapy unit: role of cross infection and host factors

Despite the sparsity of Pseudomonas aeruginosa in the environment colonisation and infection with this organism was found at several sites by selective culture in 20 out of 46 patients in an intensive therapy unit. Three patients developed Ps aeruginosa pneumonia. Serial serogrouping and phage typing identified multiple strains in the unit and in the same patient. Rectal carriage occurred in 16 patients but rectal strains did not subsequently appear in tracheal aspirates; strains varied in their affinity for the upper respiratory tract. Colonisation was not directly related to length of stay and was detected in 16 of those colonised within 24 hours of admission. In intubated patients, who were colonised more frequently than those not intubated, upper respiratory tract colonisation correlated strongly with low initial arterial pH values. Personnel were probably responsible for cross infection among patients when the unit was busy. Strain differences and the susceptibility of patients also influenced colonisation and infection. Elimination of major reservoirs of Ps aeruginosa and compliance with procedures to control cross infection remain essential if patients in hospital are to escape colonisation by the organism.

Epidemiology and prevention of pseudomonas aeruginosa chest infection in an intensive care unit

An epidemiological investigation of Pseudomonas aeruginosa in an Intensive Care Neurosurgical Unit has shown that there were epidemic, endemic and endogenous types present simultaneously. These pseudomonads were cultured from purulent sputa postoperatively and sometimes caused systemic disease. The epidemic type was traced to a ventilator and a nebulizer whilst the endemic and endogenous types were not found in environmental sites. Effective decontamination of equipment and the use of bacterial filters where possible are essential in preventing the spread of infection. Staff hygiene remains important, particularly hand washing with antiseptic soap preparations.

Cross-infection from contaminated anaesthetic equipment. A real hazard?

A definite relationship between the use of contaminated anaesthetic equipment and subsequent pulmonary infection remains to be established. There is however indirect and circumstantial evidence suggesting that cross-infection may occur, and further an increased susceptibility of surgical patients to pulmonary infections has been demonstrated. Decontamination should be recommended before the equipment is re-used. Pasteurisation may prove sufficient and this can be obtained employing a specially designed dish-washing machine.

Bacterial filters - are they necessary on anaesthetic machines?

At the Vancouver General Hospital the effectiveness of the system for decontamination of anaesthetic equipment was evaluated to determine the need for bacterial filters on anaesthetic machines. Two groups of patients were studied. Group I consisted of 33 patients, none of whom had clinical symptoms of respiratory tract disease. Group II consisted of 17 patients who had lower respiratory tract secretions. In the latter group 16 had chronic bronchitis and had cystic fibrosis. Of 550 bacterial cultures taken from the anaesthetic equipment immediately before and after anaesthesia in our 50 patients, only five yielded a growth of non-pathogenic bacteria. The results of this study indicate that bacterial colonization of anaesthetic equipment is of a low order and is adequately controlled by pasteurization even after use in patients with chronic lower respiratory tract disease. The use of bacterial filters does not appear justified if a strict regimen of cleaning and pasteurization is followed.

Early postsurgical bacterial contamination of the airways: a study on 28 open-heart patients

One pre- and two postoperative cultures of tracheo-bronchial secretions were obtained from 28 cardiac patients, subjected to open-heart surgery. Four patients received preoperative antibiotics, and all but one received postoperative prophylactic antibiotics. Preoperatively, only one patient had potential pathogens; after surgery (mean intubation time 4.2 h), four patients (14.3%) had organisms; and after 19 h of intubation, 28% of the patients had potential pathogens in their tracheo-bronchial secretions. Only three of the seven organisms recovered from the last sample were clearly sensitive to the antibiotics given prophylactically; and two of these organisms were Group A beta-haemolytic streptococci. The early presence of organisms in the airways after intubation, the high incidence of colonization, and the ineffectiveness of prophylactic antibiotics in preventing this contamination are pointed out. The factors that may possibly influence colonization of airways among these patients are commented on.

Agricultural plants and soil as a reservoir for Pseudomonas aeruginosa

Pseudomonas aeruginosa was detected in 24% of the soil samples but in only 0.13% of the vegetable samples from various agricultural areas of California. The distribution of pyocin types of soil and vegetable isolates was similar to that of clinical strains, and three of the soil isolates were resistant to carbenicillin. Pseudomonas aeruginosa multiplied in lettuce and bean under conditions of high temperature and high relative humidity (27 C and 80-95% relative humidity) but declined when the temperature and humidity were lowered (16 C, 55-75% relative humidity). The results suggest that soil is a reservior for P. aeruginosa and that the bacterium has the capacity to colonize plants during favorable conditions of temperature and moisture.