James Martins, MSc (c), BSc, Bevin McMullin, PhD, MappSc, RRT, Chris Miller, PhD, BA, RRT
Patients performing lung function tests at home have expressed concerns as to whether they need to use pulmonary function filters on their spirometers. Considering the cost of filters, it could be a barrier to performing frequent measurements. We explored the impact of patients exhaling microorganisms into their spirometer without use of a filter and the likelihood of them re‐infecting themselves with subsequent tests.
Background
For almost two centuries, spirometers were used by patients without complete circuit disinfection between patients.
Hygiene was limited to changing out the mouthpiece that went in the patient’s mouth. In the early 1900’s, some institutions using volumetric measuring devices such as dry rolling seal, wedge or water seal spirometers would change the hoses, valve and mouthpiece between subjects without concern for cross contamination from the air in the spirometers. It wasn’t until the mid to late 1970’s that institutions began using spirometer filters on their equipment to minimize the risk of cross contamination.
There have been limited reports in the literature regarding the potential for cross contamination using spirometers. While there have been a handful of studies reporting on the bacterial load in spirometers, there is only one in‐vivo study evaluating the mobilization of microorganisms between patients. Burgos, et al, studied the contamination of spirometers in fifty‐four patients and then the actual effect on subsequent patients.1 They disinfected their spirometers before starting the trial and then sampled after each patient. Ninety percent (90%) culture samples from the water‐sealed spirometer showed microbial growth with prevalence of Penicillium sp. (62%), Pseudomonas fluorescens (32%), and Burkholderia cepacea (48%). While they were able to demonstrate contamination of the spirometer,
they found that they could not demonstrate any transmission sequence of potentially pathogenic microorganisms from the equipment to patients or vice versa.
One of the only studies suggesting microbe mobilization from spirometers was by Bracci, et al.2 Using a mechanical syringe system they pulled air back into the syringe through a microbial collection filter from an unfiltered spirometer.
These spirometers were used on a patient immediately before a test on a subsequent patient and they identified the potential for microbe mobilization between patients. Their conclusion was that this droplet contamination was more likely when spirometers were used immediately between subjects. They also found that turbine spirometers mobilized
more organisms than Fleisch type flow meters attributing it to the spinning vane. However, they hypothesized that “use of a heated pneumotachograph, or drying the spirometers between subjects, would probably have reduced the risk of bacterial mobilization related to the presence of condensation and droplets of sputum”. Zhang, also suggested flushing air through the sensor by a calibration syringe or an unheated hairdryer after each subject to remove condensation to reduce the likelihood of cross contamination.3
Heibert, et al.4 studied the retrieval of nonpathogenic Escherichia coli after aerosolizing organisms into standard pulmonary function tubing for volume spirometers. The arrival of the aerosol at the distal end of the tubing was documented by culture. After delays of 0, 1, 5, and 10 min, respectively, air was forcibly withdrawn from the proximal end of the tubing through a special petri plate assembly. The plates were cultured and the colonies were counted. Immediately after insufflation of organisms, air withdrawn from the proximal tubing had counts similar to the air sampled at the distal end. After a 1‐min delay, the proximal samples contained only rare organisms.
No organisms were recovered from proximal air samples after a delay of 5 or 10 min after insufflation of organisms. They concluded that “the absence of detectable aerosolized E. coli after delays of 5 and 10 min after insufflation of organisms into spirometry tubing supports the hypothesis that a significant transfer of aerosolized organisms does not occur during routine pulmonary function testing as long as an interval of 5 min or more is allowed between tests.”
Kendrick, et al.,5 reported on a practical approach to infection control in lung function and included a review much of what has been reported in the literature. While concluding that there is no data to indicate cross contamination between patient from lung function equipment, they noted that there is no data on unheated spirometers, turbine spirometers or hot‐wire spirometers.
Pulmonary function filters are single use items costing between $0.35 and $2.00 each. For patients self‐testing at home on a daily basis, this cost could make the test financially prohibitive. Because these patients usually test themselves once a day, it was determined that we should test the effects of heavy contamination of a turbine spirometer that was allowed to rest overnight and then tested the following day for microbe mobilization.
Purpose
To test whether a single‐patient use spirometer would likely re‐ inoculate a patient with their own bacteria when reused without a filter.
Procedure
Each test series was done in two stages, a turbine contamination stage followed by 24 hours in a warm room temperature incubator and then followed by a stage where the mobilization of bacteria was evaluated. These were performed with both aerosolization contamination and direct swab placement of bacteria.
Aerosolized Contamination
Stage 1
Pseudomonas aeruginosa was grown in BHI broth overnight. Bacteria was diluted in saline to achieve a 105 cfu/mL concentration. Three (3) mL of the microbial solution was added into a standard small volume nebulizer which was attached to the mouthport side of the turbine from a GoSpiro® (Monitored Therapeutics, Inc, Dublin, OH) spirometer. Using 6 L/min air flow, the solution was aerosolized for about 30 seconds. A Blood‐Heart‐Infusion (BHI) agar plate was placed approximately 1 cm below the exit port of the spirometer turbine to catch aerosolized bacteria to confirm the delivery of the P. aeruginosa. A swab was also taken from the inside of the spirometer turbine outlet and plated.
The plates were placed into a 37°C incubator while the spirometers were placed into sterile containers and in a 30°C incubator overnight to simulate a warm environment that might be more amenable to bacterial reproduction and growth. This procedure was repeated for three (3) turbines.
Stage 2
The following day, each spirometer turbine was connected at its outlet to a 3 L syringe from the bottom side (Figure 2). Three litres of air were pumped at >300 L/min to simulate inhalation back through the device. On the mouth side a BHI plate was placed about 1 cm below the mouthport of the spirometer turbine in a similar position and distance to contamination stage to capture any aerosolized bacterial particulates. This was performed for the three turbines.
Results
Confirmation of contamination was demonstrated by confirming bacterial growth after aerosolizing the bacterial suspension and through the growth that was found from samples obtained during the aerosolizing process (Figure 3a). However, no bacterial growth was found from samples obtained from swabbing or forcibly blowing air through the opposite end (Figure 3b).
Direct Bacterial Contamination
Stage 1
The following procedure was done to represent a full positive contamination with a large bacterial surface contamination within the spirometer. P. aeruginosa was grown in BHI broth overnight. Bacteria (~108 cfu/mL) was swabbed directly onto the spirometer turbine at both the elbow that is located very proximal to the patient interface and on the internal bladesat the distal area of the spirometer. From a smaller area than the inoculation, a swab surface sample was taken as a positive control and plated onto BHI plates to confirm contamination.
The plates were placed into a 37°C incubator while the spirometer turbines were placed into sterile containers and in a 30°C incubator overnight to simulate a warm environment that might be more amenable to bacterial reproduction and growth. This procedure was repeated for three (3) turbines.
Stage 2
The following day, each spirometer turbine was connected at its outlet to a 3 L syringe from the bottom side (Figure 2). Three litres of air were pumped at >300 L/min to simulate inhalation back through the device. On the mouth side a BHI plate was placed about 1 cm below the mouthport of the spirometer turbine in a similar position and distance to contamination stage to capture any aerosolized bacterial particulates. This was performed for the three turbines.
Results
No bacterial growth was found from samples obtained by forcibly blowing air back through the device towards the proximal end where the patient would be inhaling through their mouth (Figure 4b). To confirm the continued presence of bacterial growth within the device, a swab sample was taken from the inner surface of the elbow of the spirometer turbine and incubated for another 24 hours. This sample showed bacterial growth on the BHI plate (Figure 4c).
Conclusion
Based on these data, and assuming patients wash the mouthport adapter from the spirometer and allow their turbine to dry overnight, it is unlikely that a subject will re‐inoculate themselves by re‐using the spirometer without a filter. We conclude that there is a very low to no chance that bacteria will be aerosolized and then subsequently inhaled and that it is safe for single patients to use their home spirometer without a filter. We do note that for some spirometers, there might be a concern with large exhaled particle altering the characteristics of the flow sensor such as in Fleisch type pneumotachs and causing these sensors to produce erroneous results. Each spirometer should be evaluated individually to determine if this is a concern.
References
- M. Bracci, E. Strafella, N. Croce, S. Staffolani, A. Carducci, M. Verani, M. Valentino, L. Santarelli. Risk of bacterial cross infection associated with inspiration through flow‐based spirometers. Am J Infect Control 2011; 39:50‐5.
- F. Burgos, A. Torres, J. Gonzáles, J. Puig de la Bellacasa, R. Rodriguez‐Roisin, J. Roca. Bacterial colonization as a potential source of nosocomial respiratory infections in two types of spirometer. Eur Respir J, 1996; 9:2612–2617
- Zhang Y. Using barrier filters to protect spirometer sensors from droplet deposition. Chest. 2005; 127(6):2294
- Hiebert T1, Miles J, Okeson GC. Contaminated aerosol recovery from pulmonary function testing equipment. Am J Respir Crit Care Med. 1999; 159(2):610‐2
- Kendrick AH1, Johns DP, Leeming JP. Infection control of lung function equipment: a practical approach. Respir Med. 2003; 97(11):1163‐79.
