We commend Lee et al. on their attempt using a real-time particle monitor to detect possible aerosol generation from phacoemulsification.1 Such devices can be powerful tools to assist with bioaerosol exposure assessment, but the generated real-time data should only be used as surrogate data and interpreted with great caution.
The very low total cumulative particle counts from very short-grab sampling collection time of 21-second windows might not have sufficient signal-to-noise ratio for numeric quantification. The typical estimated limit of detection—the value above which it is considered truly detectable—and limit of quantification—value above which it is considered quantifiable—are 3× and 10× SD, respectively.2 Because the short sampling duration, particle counts were near or below limit of detection, thus offering low confidence to the reported values. Moreover, because the measured mean particle counts for all experiments were below limit of quantification, the reported numbers could be neither accurately quantified nor compared.
To improve accuracy, a longer sampling time of several minutes is recommended. To rule out buildup of bioaerosol from multiple operations, full-shift (8 hours) personal monitoring at the breathing zones of the operating personnel is also recommended. The volume of the room along with air change rate should be stated to help standardize equivalent observation in other room settings. The number of occupants in the room, temperature, relative humidity, and so on should also be noted to ensure that the observed data would not be affected by interday variations.
SARS-CoV-2 virus particle sizes were reported to exist as a continuum from less than 0.3 to more than 5 μm.3 An aerodynamic characterization study at Wuhan Hospital suggested virus particles found in the personal protective equipment doffing room were predominantly small particles between 0.25 and 0.5 μm.4 Therefore, it is crucial for any particle size study to accurately capture bioaerosol at all size ranges including size less than 0.3 μm. The data from Lee et al., suggesting no elevation of bioaerosol observed from less than 0.3 to 10 μm, was based on the TROTEC PC200 (Trotec GmbH) optical particle counter, which has a stated detection range between 0.3 and 10 μm diameter. Although it is claimed that the monitor can quantify particles below 0.3 μm, the accuracy of particle detection of less than 0.3 μm is highly questionable. As per instrument specification, the counting efficiency of 0.3 μm particle was reportedly only 50% at best.5 It is, therefore, unsure whether the monitor can detect particles smaller than 0.3 μm. If so, what is the counting efficiency for these smaller particles? Thus, the low count of particles at less than 0.3 μm range in the study might be insufficient to rule out fine bioaerosol generation during simulated phacoemulsification. Recommendations to lower personal protective equipment might be premature, especially when the major part of bioaerosol production in the operating environment is expected to be generated from the respiratory tracts of patients and staff, which is not captured in this simulation study.
1. Lee H, Naveed H, Ashena Z, Nanavaty M. Aerosol generation through phacoemulsification. J Cataract Refractive Surg 2020 [Epub ahead of print.]. Available at https://journals.lww.com/jcrs/Fulltext/9000/Aerosol_generation_through_phacoemulsification.99841.aspx
2. Shrivastava A. Methods for the determination of limit of detection and limit of quantitation of the analytical methods. Chron Young Scientists 2011;2:21–25
3. ASHRAE. Position paper on infectious aerosols [online]. 2020. Available at: https://www.ashrae.org/file%20library/about/position%20documents/pd_infectiousaerosols_2020.pdf
. Accessed July 23, 2020
4. Liu Y, Ning Z, Chen Y, Guo M, Liu Y, Gali NK, Sun L, Duan Y, Cai J, Westerdahl D, Liu X, Xu K, Ho KF, Kan H, Fu Q, Lan K. Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals. Nature 2020;582:557–560
5. Trotec PC200 Particle Counter Operating Manual. Trotec GmbH & Co. KG. Available at: https://uk.trotec.com/fileadmin/downloads/Messgeraete/Emission/PC200/TRT-BA-PC200-TC-004-EN.pdf
. Accessed June 28, 2020