Effect of relative humidity on the survival of airborne opportunistic Gram-negative pathogens

Abstract number: P1530

Airey P.J., Beggs C.B., Kerr K.G., Snelling A.M.

Objectives: There is increasing evidence that the hospital environment plays a major role in nosocomial infections. Bacteria can be disseminated to both patients and surfaces via the air, but it is not clear how readily different opportunistic pathogens persist in an airborne state. We investigated the ability of 4 such Gram negative species to survive in air under conditions typical of a ward environment, and looked at the effect of changing relative humidity (RH) as a potential control measure.

Methods: Representative isolates of Acinetobacter baumannii, Steno­trophomonas maltophilia, Burkholderia cepacia and Pseudomonas aeruginosa were nebulised (in water) into a 72m3 aerobiological chamber, in which temperature, relative humidity (RH) and ventilation rate was controlled. Air was sampled at 10–15 min intervals using a 6-stage Anderson sampler, and surviving bacteria recorded as cfu/m3 of room air. Firstly survival rates under ambient (50% RH, 23°C) conditions were determined in a series of decay-curve experiments. Then, under steady-state conditions, the effects of RH under two ramping humidity profiles were investigated. Bacteria were nebulised into the chamber for 240 min with RH held at 30% (LOW) for the first 80 min, 50% (AMBIENT) for the central third (80–160 min) and 70% (HIGH) for the final 80 minute phase (160–240 min). In repeat experiments the humidity profile was reversed (i.e. HIGH-AMBIENT-LOW for consecutive 80min periods).

Results: Bacteria were nebulised into the chamber to a concentration of ~104 cfu/m3. There was an immediate 3-log decrease in counts observed with each species on the decay curves. However, viable cells were still recovered from the air after 90mins, for all species except P. aeruginosa.

In the steady-state experiments (bacterial numbers maintained at an input of ~104 cfu/m3) the number of cfus recovered was 1–2 log higher at 70% RH than 50% RH. Few, or in most cases no, cfu/m3 were recovered in the dry, 30% RH phases for three of the species. In contrast, larger numbers of B. cepacia were always recovered (~100 cfu/m3) at low RH.

Conclusion: Low levels of three of these Gram negative nosocomial pathogens can survive in an airborne state for at least 90 min, which would facilitate their dissemination around a ward space. These results suggest that, by reducing the RH, even for a short period, such dissemination could be limited, thereby helping to reduce cross-infection of patients and contamination of surfaces.

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
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