Selective Nonroutine Microbial Surveillance of In-Use Hospital Nebulizers by Aerosol Entrapment and Direct Sampling Analyses of Solutions in Reservoirs

Abstract

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.

Direct dilution sampling, quantitation, and microbial assessment of open-system ventilation circuits in intensive care units

“…The inspiratory effluent or aerosol entrapment method has been traditionally used to assess RT equipment; however, the direct sampling technique is apparently more sensitive (detecting .10 CFU/ml) than at least one aerosol entrapment method we tested previously (20). Direct sampling, thus, can assist in the detection of low numbers of microbes that have the potential to serve as infective agents in the compromised host.…”

“…Currently, respiratory infections are the third most common type of nosocomial disease (10,25). Because of the persistence and regularity of reservoir contamination in several hospitals, we expanded our direct dilution method of sampling (19) and evaluated other surveillance methods for their potential value in assessing microbial burdens of in-use RT equipment and solutions (20,21). An additional and hitherto unemphasized potential problem is the breathing circuitry of in-use RT equipment and its management by personnel.…”

Limulus amoebocyte lysate and direct sampling methods for surveillance of operating nebulizers

“…Also isolated were the fermentative bacteria Flavobacterium meningosepticum, Enterobacter cloacae, and Staphylococcus sp. DISCUSSION Our experiences clearly indicate that the use of contaminated nebulizing RT equipment on patients is a problem that still occurs in some hospitals (25)(26)(27). There is a need to detect contamination problems before the situation arises in which the only alert is an occurrence of nosocomial disease in one or more patients.…”

“…Furthermore, abuses or improper maintenance of RT nebulizing equipment within 24-h operating periods may occur. In these situations, or when there are actual or suspected epidemics associated with RT, it is sometimes necessary to determine the nature and extent of microbial contamination as an index of the cleanliness of the equipment and its suitability for further use (6,21,24,27,28). The value of selective surveillance, particularly for RT, has been noted (4, 7).…”

“…We designed the direct dilution sampling procedure for this purpose (26). We recently reported on a comparison of this procedure with the Aero-Test device (27).…”