In a systematic approach, 37 duplicate samples of open system circuits (Bennett MA-1 ventilators) of patients in medical and surgical intensive care units were processed by direct and serial (APHA guidelines) dilutions. The paired difference test on 15 of the in-use circuitry solution samples indicated no difference between the direct and serial dilution methods (P < 0.001). Seventy-seven additional respiratory therapy circuitry samples from similar intensive care patients were analyzed via a direct dilution method alone and processed microbiologically. The direct dilution procedure was a rapid and accurate means of evaluation of microbial contamination in the range of .10 to s106 CFU/ml. High densities of organisms frequently were found. Sites of contamination included the proximal or patient end of the circuitry (heaviest), the nebulizer trap, and the distal or humidifier portions of the circuitry. The contaminants found were predominantly gram-negative nonfermenters: Acinetobacter calcoaceticus var. antitratus, Pseudomonas aeruginosa, Pseudomonas maltophilia, and Flavobacterium meningosepticum. Fermenters were Klebsiella pneumoniae, Proteus sp., Enterobacter cloacae, Citrobacter diversus, and Enterobacter agglomerans. Infrequently, gram-positive Streptococcus spp. and Staphylococcus spp. were noted.
Effluent aerosols and liquid reservoir samples from 255 in-use hospital nebulization devices were analyzed by Aero-Test samplers (Olympic Corp.) and direct dilution procedures (0.1-, 0.01-, and 0.001-ml plated samples). Thirty-five percent (89 of 255) of the in-use hospital reservoir samples were positive by direct dilution, and 24% (61 of 255) were positive by Aero- Test samplers. Acinetobacter calcoaceticus var. anitratus was found either alone or in association with Pseudomonas spp. in 50% of all the contaminated in-use reservoirs. This indicates a high endemicity for Acinetobacter in the environment studied. Viable microbes in the reservoirs of contaminated nebulizers ranged from as few as 20 to >2 × 10 5 colony-forming units/ml. Microbial contamination at moderate to heavy levels (1 × 10 4 to >2 × 10 5 ) was regularly detected by both procedures. Microbial densities of 10 3 colony-forming units/ml and less in contaminated reservoirs often were negative in the Aero- Test but positive by direct dilution techniques. These hospital-based results were similar to laboratory data obtained with sterile nebulizers intentionally contaminated in graduated densities with either Staphylococcus aureus or Pseudomonas aeruginosa . Sensitivity of the Aero- Test system was best when ≥10 4 colony-forming units/ml were present in the reservoirs of operating nebulizers. The manufacturer suggests that five or less colonies appearing after sampling on Aero- Test plates upon 48-h incubation does not indicate contamination of the reservoir. Our data show that even a single colony, particularly if it is typical, water-associated, gram-negative bacterial species, may well indicate low levels of reservoir contamination. Both the Aero- Test and direct dilution methods indicated the need for more rigorous management of the in-use respiratory therapy equipment in the hospital surveyed. These studies demonstrate the value of selective nonroutine surveillance for identifying potential or actual contamination problems of in-use nebulizing equipment, particularly when recommended care guidelines are not followed due to choice or unawareness. Ameliorative-corrective measures, which included routine 24-h substitution of old units with new sterile units, were initiated as a result of this surveillance program.
One hospital sought to study the differences in using resterilizable permanent versus disposable ventilator circuits and changing the circuits on a 24-h versus a 48-h basis. Over a period of 13 months 656 condensate samples from 92 permanent and 72 disposable circuits were collected and plated by a loop dilution technique. Two samples were collected from the inspiratory limb (humidifier; tubing or nebulizer), and two were collected from the expiratory limb (tubing and trap) of each circuit. Contamination rates were higher for disposable circuits than for permanent circuits and for 48-h changes than for 24-h changes. Results of x2 testing by site indicated there was more contamination on the inspiratory and expiratory limbs each with use of disposàb1l circuits than with the use of permanent circuits. The total results (X2 analysis) showed significantly greater microbial growth with the use of disposable circuits (permanent versus disposable, P < 0.001) and extension of time to 48-h changes (24 h versus 48 h, P < 0.05). In the experience of this hospital permanent circuits proved more advantageous from the standpoint of contamination risk and cost.
The contamination of semiclosed disposable circuits of Healthdyne and Bourns ventilators was studied in a newborn intensive care unit over a 2-year period. A total of 379 fluid samples was obtained from inspiratory and expiratory tubing condensates and traps and from thermal humidifier columns fed with prefilled containers of sterile water. In addition, 100 tryptic soy agar plates were exposed to the exhalation mist of the circuits sampled. With 24-h changes of circuits a 2.5% contamination rate was observed (phase I). In an effort to contain costs, circuits were changed every 48 h (phase II); the concentration of potential pathogens increased to >105 CFU/ml with this extension of changing time. Two long-term (15and 9-month) infants were colonized and intermittently infected, one with Klebsiella pneumoniae and Staphylococcus aureus and the other with Pseudomonas aeruginosa. When the protocol was readjusted from 48to 24-h circuit changes (phase II), the contamination rate decreased; for the two colonized infants (35 circuits, 123 samples) the contamination rate decreased from 19 to 6% (P < 0.01; chi-square test), and for seven noncolonized infants (59 circuits, 217 samples) the contamination rate decreased from 5 to 0.5% P < 0.001; (chi-square test). These data suggest that frequent changing of the circuits reduces colonization and cross-infection.
The Limulus amoebocyte lysate test for detection of endotoxin (Pyrogent; Mallinckrodt Chemical Co.) and the Easicult method (Orion Diagnostica) for detection of bacteria were compared with direct dilution sampling, a standardized technique for respiratory therapy surveillance previously developed in our laboratory. Tests of 206 reservoirs of nebulizers were done in three hospitals in Georgia. Forty-five percent of all reservoirs sampled were contaminated. Gramnegative, nonfermentative bacilli were the predominant contaminants. The results of the Limulus test and the Easicult system were in agreement with those of the direct dilution sampling tests approximately 84 and 90% of the time, respectively. Direct dilution of water samples onto blood agar plates was the most sensitive, reliable, and informative method for detecting viable bacteria. The Easicult and Limulus systems were sensitive enough to detect _103 colony-forming units per ml. Positive Limulus tests and negative culture tests, reflecting detection of endotoxin but not of viable gram-negative bacteria, occurred in 20 of 206 (9.7%) instances. Positive cultures and negative Limulus tests were noted in 13 of 206 (6.8%) samplings. The Limulus test is a valuable procedure, for it can detect moderate-to-heavy microbial contamination within 1 h of testing and affords the opportunity to remove contaminated equipment from patients within minutes of a positive test result. These results demonstrate the potential value of the Easicult and Limulus tests for selective surveillance of operating nebulizers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.