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. 2022 Aug 2;11(8):871.
doi: 10.3390/pathogens11080871.

Efficacy of Dry Heat Treatment against Clostridioides difficile Spores and Mycobacterium tuberculosis on Filtering Facepiece Respirators

Aswathi Soni  1 , Natalie A Parlane  2 , Farina Khan  2 , José G B Derraik  3 , Cervantée E K Wild  3   4 , Yvonne C Anderson  3   5   6   7 , Gale Brightwell  1   8
Affiliations

Efficacy of Dry Heat Treatment against Clostridioides difficile Spores and Mycobacterium tuberculosis on Filtering Facepiece Respirators

Aswathi Soni et al. Pathogens. .

Abstract

The COVID-19 pandemic has required novel solutions, including heat disinfection of personal protective equipment (PPE) for potential reuse to ensure availability for healthcare and other frontline workers. Understanding the efficacy of such methods on pathogens other than SARS-CoV-2 that may be present on PPE in healthcare settings is key to worker safety, as some pathogenic bacteria are more heat resistant than SARS-CoV-2. We assessed the efficacy of dry heat treatment against Clostridioides difficile spores and Mycobacterium tuberculosis (M. tb) on filtering facepiece respirator (FFR) coupons in two inoculums. Soil load (mimicking respiratory secretions) and deionized water was used for C. difficile, whereas, soil load and PBS and Tween mixture was used for M. tb. Dry heat treatment at 85 °C for 240 min resulted in a reduction equivalent to 6.0-log10 CFU and 7.3-log10 CFU in C. difficile spores inoculated in soil load and deionized water, respectively. Conversely, treatment at 75 °C for 240 min led to 4.6-log10 CFU reductions in both soil load and deionized water. C. difficile inactivation was higher by >1.5-log10 CFU in deionized water as compared to soil load (p < 0.0001), indicating the latter has a protective effect on bacterial spore inactivation at 85 °C. For M. tb, heat treatment at 75 °C for 90 min and 85 °C for 30 min led to 8-log10 reduction with or without soil load. Heat treatment near the estimated maximal operating temperatures of FFR materials (which would readily eliminate SARS-CoV-2) did not achieve complete inactivation of C. difficile spores but was successful against M. tb. The clinical relevance of surviving C. difficile spores when subjected to heat treatment remains unclear. Given this, any disinfection method of PPE for potential reuse must ensure the discarding of any PPE, potentially contaminated with C. difficile spores, to ensure the safety of healthcare workers.

Keywords: COVID-19; PPE; SARS-CoV-2; bacteria; deionized water; disinfection; healthcare workers; inactivation; personal protective equipment; reuse; soil load.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Presence/absence of C. difficile spores recovered on selective media (a) and non-selective media (b) on the positive controls (room temperature at 18–22 °C for 10 min) and after dry heat treatment at 85 °C for 30, 60, 120, and 240 min, while being suspended in soil load and inoculated onto filtering facepiece respirator (FFR) coupons. Each test was carried out on 6 coupons to ensure replication.
Figure 1
Figure 1
Presence/absence of C. difficile spores recovered on selective media (a) and non-selective media (b) on the positive controls (room temperature at 18–22 °C for 10 min) and after dry heat treatment at 85 °C for 30, 60, 120, and 240 min, while being suspended in soil load and inoculated onto filtering facepiece respirator (FFR) coupons. Each test was carried out on 6 coupons to ensure replication.
Figure 2
Figure 2
Presence/absence of C. difficile spores recovered on selective media (a) and non-selective media (b) on the positive controls (room temperature at 18–22 °C for 10 min) and after dry heat treatment at 30, 60, 120 and 240 min, while being suspended in deionized water and inoculated onto filtering facepiece respirator (FFR) coupons. Each test was carried out on 6 coupons to ensure replication.
Figure 2
Figure 2
Presence/absence of C. difficile spores recovered on selective media (a) and non-selective media (b) on the positive controls (room temperature at 18–22 °C for 10 min) and after dry heat treatment at 30, 60, 120 and 240 min, while being suspended in deionized water and inoculated onto filtering facepiece respirator (FFR) coupons. Each test was carried out on 6 coupons to ensure replication.
Figure 3
Figure 3
Inactivation of C. difficile spore numbers using dry heat treatment at 85 °C (a) and 75 °C (b) in a soil load (black bars) and deionized water (grey bars) inoculums. Data are the least-squares means (adjusted means) with error bars representing the respective 99% confidence intervals. **** p < 0.0001 for a difference between inoculum types at a given treatment duration. At each heat treatment temperature, all pairwise comparisons between treatment durations for a given inoculum type were statistically significant at p < 0.0001. Further, for the given treatment duration and inoculum type, all differences in the magnitude of inactivation between 75 and 85 °C were statistically significant at p < 0.0001. Controls indicate “no thermal treatment”.
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