Evaluation of the survivability of microorganisms used in breathing filters on hospital ventilators

This study assessed whether breathing filters present in ventilating machine could be a potential reservoir for the survival and growth of bacteria and mold spores.

Using a Henderson apparatus in separate experiments under controlled conditions, six different microorganisms (B. atrophaeus 10073, S. epidermidis 12721, MS-2 coliphage (virus surrogate), E. coli 9481, B. diminuta 11091 and Aspergillus brasiliensis (formerly niger) ATCC 16404) were sprayed onto membranes from breathing filters. The contaminated loaded filter membranes were then attached to an experimental rig through which clean air was drawn at a constant rate, in order to simulate the use of the membrane filter for six days. The results included:

No decline in the viability of B. atrophaeus spores was found when the hydrophobic membranes were placed on the air flow experimental test rig over a minimum of 6 days.
In long term experiments, B. atrophaeus spores survived on the filter membrane for 7 months.
MS-2 coliphage and A. Niger showed the same resistance with very little decrease in viability.
With a 5- log reduction S. epidermidis demonstrated the least ability to survive over the 6 day period.
E. coli and B. diminuta were found to be the least stable of all microorganismsms tested, with no recovery after 24 hours.

These experiments indicate that microorganisms will survive on breathing filters used in ventilation machines. There is therefore a potential for cross infection between patients when such equipment is used.

Last reviewed: 25 October 2010