Infection control in the respiratory laboratory: risk, costs, expediency

The article by Side et al.,¹ on pages 9-14 of this issue of the Journal, concerning infection control in the respiratory laboratory, raises the highly controversial issue of how best to prevent cross infection between patients sharing use of lung function testing equipment. This study compares the costs of two approaches to infection control. It is not able to address the benefit side of the balance and indeed there are very few firm data regarding either risk or benefit against which costs need to be evaluated.

In this age of highly transmissible disease such as viral hepatitis, of infectious diseases with catastrophic consequences for the individual such as HIV infection, and of significant numbers of persons with immuno-suppressive illnesses and treatments, there are a number of complex issues surrounding how best to primum non nocere in the lung function context. Spirometers and other devices from which our patients may be required to, or inadvertently breathe in, do of necessity, have nooks and crannies in which lurking organisms may flourish. Aerosolisation of organisms from internal surfaces of such equipment is a theoretical but inadequately documented risk.

The Thoracic Society of Australia and New Zealand guidelines for infection control in respiratory laboratories² are based on a universal precautions approach. They advocate decontamination of equipment by (i) between-patient sterilisation of 'critical' items entering tissue, cavities or blood vessels, eg vascular catheters; (ii) between-patient disinfection of 'semi-critical' items, eg non-disposable mouthpieces; and (iii) thorough daily cleaning with detergent of 'non-critical' items, eg spirometer tubing distal to a breathing valve. The temporal and financial implications of such a policy, however, are considerable and mitigate against full implementation of the guidelines. These factors - the ever advancing principle of cost containment in the health care system, the health hazards imposed by chemical exposure for laboratory staff and commercial influences, such as the deleterious effects of chemical solutions on equipment - have all conspired in the search for a short cut to the housekeeping - in this case, some mechanism for keeping the patient's microbial flora inside the patient and out of the equipment.

Considerable ingenuity has been applied to this task. An exquisitely simple approach has been adopted by Denison et al.,³ who suggest having the patient breathe in and out of a disposable plastic bag. This in turn displaces air within a volume measuring device or can have its gaseous contents analysed separately from their owner and other patients, by outboard sampling. This prevents the output from the gas analyser from returning to the patient's breathing circuit.

An alternative strategy is to place a disposable filter between the subject and the measurement equipment from which the next patient is required to rebreathe. The efficiency of such filters has previously been sadly short of the mark, but a more recent development is the new high-efficiency Hyper Filter disposable barrier constructed of material with 99% efficiency at excluding bacteria at physiological flow rates.⁴ We do not yet know, however, the efficiency of these filters at excluding viruses and other microbes smaller than bacteria.

Until now the commonly held view is that universal precautions remain appropriate because alternative approaches have not yet been demonstrated sufficiently safe. The problem is that most respiratory function laboratories do not have the staffing and time to instigate these practices fully, and there is no evidence base establishing the risks of cross infection as sufficient to justify all this cleaning, disinfecting and sterilising for every new patient.

The real outcome of interest in this risk management exercise, however, is how many patients actually develop clinical infection from respiratory function unit equipment used by others. Certainly organisms such as Pseudomonas,⁵ Burkholderia cepacia, Haemophilus influenzae⁶ and acid fast bacillae⁷ have been recovered from spirometers, but the number of reported cases of infection from such sources have to date been few and far between. The vagaries of missed cases, unreported cases, publication bias and the impracticality and expense of randomised controlled studies in this setting have mitigated against accumulation of an evidence base to demonstrate risk at the clinical level. Modelling of the possibility of microbial escape from equipment using bits of tubing, bicycle pumps and Petri dishes can go some way to enhance our feelings of security. However, this cannot replace the true biological data required to establish properly the risks of cross infection as a basis for determining the benefit of any infection control approach to be weighed against its costs.

Recent NSW legislation has been passed regarding the use of filters in anaesthetic circuits following reported cases of possible cross infection. Reliance on filters or plastic bags for that matter, however, will always leave open the possibility that transmissible agents capable of getting through, whatever the pore size, will emerge to cause future disease transmission in particular physical and clinical circumstances.

We need to be confident that the procedures and equipment we use to test our patients are safe. Although the risks of cross infection from respiratory function testing would appear to be low, more comprehensive studies evaluating the risks are needed before we can properly subject the cost of any infection control programme to rigorous cost-benefit evaluation.

R. J. PIERCE,
Professor,
Respiratory Medicine,
University of Melbourne,
Director,
Thoracic Services,
Austin and Repatriation Medical Centre,
Melbourne, Vic.

References

1. Side EA, Harrington G, Thien F, Walters EH, Johns DP. A cost-analysis of two approaches to infection control in a lung function laboratory. Aust NZ J Med 1999; 29: 9-14.
2. Crockett AJ, Grimmond T. Guidelines for infection control in the respiratory function laboratory - a position paper of the Thoracic Society of Australia and New Zealand. Thoracic Society News 1993; 4: 6-7.
3. Dension DM et al. Lung function testing and AIDS. Respir Med 1989: 133-8.
4. Kendrick AH, Milkins C, Smith EC, Lemmings J, Benbough JE. Assessment of Spiroguard and Vitalograph bacterial filters for use with lung function equipment. Am J Resp Crit Care med 1998; 157: A175.
5. Ilses A, Maclusky I, Corey M et al. Pseudomonas cepacia infection in cystic fibrosis: an emerging problem. J Pediatr 1984; 104: 206-10.
6. Gough J, Kraak WAG, Anderson EC, Nichols WN, Slack MPE, McGhie D. Cross infection by non-encapsulated Haemophilus influenzae. Lancet 1990; 336: 159-60.
7. Hazaleus RE, Cole J, Berdischewsky N et al. Tuberculosis skin test conversion from exposure to contaminated pulmonary function testing equipment. Respir Care 1981; 26: 53-5.