Can Breathing Filters protect against the spread of the Hepatitis C virus?

One in one hundred anesthesia patients may carry the Hepatitis C virus (HCV)3. Despite pre-operative testing and precautionary measures, asymptomatic patients may undergo surgery unnoticed. In a recent case report from the University of Amsterdam[1] it was not only that the patient was undiagnosed for the Hepatitis C Virus, but also had massive lung bleeding and was therefore able to contaminate the anesthesia breathing equipment. The hospital operated under the assumption, that their patient side filter would retain liquid contamination and that it was safe to use the circuit for the following patients. Dried out, HCV-containing blood flakes from the breathing circuit, which were found on the machine side of the filter on one of the following cases, showed that this assumption was wrong.

The device used was a so-called electrostatic breathing filter. Because of the open micro-structure of electrostatic filter media, a small sheet of media still gives an acceptable flow resistance. Electrostatic breathing filters can therefore be small, are not too complex to produce, only need small amounts of filtration media, and usually can be made at an attractive cost. On the downside they have been shown to present only a weak barrier to liquids and the contaminants contained therein.[2] The blood-borne HCV has no difficulty to pass through the electrostatic filter to the clean side of the anaesthesia system, as shown above.?

The authors of the case report from Amsterdam point out the fact, that on the other side mechanical filters have a higher performance in retaining liquid-borne contaminants.

The Pall Ultipor 25 is a hydrophobic mechanical filter. By nature of its hydrophobic (water-repellent) filtration medium it acts as a reliable barrier against liquid-borne contaminants. This has been demonstrated in the Ultipor 25’s validations to retain blood-borne viruses (Hepatitis C Virus[3], HIV[4]), but also air-borne human pathogens (e.g., Mycobacterium tuberculosis[5], Influenza A[6], SARS-CoV-2[7]).

?Can Breathing Filters protect against the spread of the Hepatitis C virus? Yes, some can!

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References

[1] Pel M.E. at al. (2022). Delayed recognition of breathing system contamination with blood containing hepatitis C virus following failure of a heat and moisture exchange filter. Anaesth Rep; 10(1):e12171

[2] Cann C. et al. (2006). The pressure required to force liquid through breathing system filters. Anaesthesia; 61: 492–497

[3] Lloyd G. et al. (1997). Barriers to hepatitis C transmission within breathing systems: efficacy of a pleated hydrophobic filter. Anaesth Intensive Care; 25(3):235-8

[4] Lloyd G. and Howells J. (1997) Efficacy of a pleated hydrophobic filter as a barrier to human immunodeficiency virus transmission within breathing systems. Centre for Applied Microbiology and Research Report

[5] Speight S. et al. (1995). Efficacy of a pleated hydrophobic filter as a barrier to Mycobacterium tuberculosis transmission within breathing systems. Centre for Applied Microbiology and Research Report.

[6] Heuer J.F. et al. (2013). Can breathing circuit filters help prevent the spread of influenza A (H1N1) virus from intubated patients? GMS Hyg Infect Control; 29: 8(1)

[7] Spiers S. & Quarti C. (2021). Filtration Efficiency of the Pall Ultipor 25 for SARS-CoV-2. Pall SLS Technical Report

Author:

Dr. Wolfgang Hares, MSc PHD- Sr. Global Manager Scientific Affairs for Gas Filtration and Respiratory Care

He supports with a range of products, which includes filters for mechanical ventilation, surgical and medical gas applications, and pulmonary function testing. He has held several roles in regional and Global marketing functions and holds a MsSc from the University of Cologne and a PhD in Biochemistry from the University Hamburg, Germany.