SARS-CoV-2 and Health Care Worker Protection in Low-Risk Settings: a Review of Modes of Transmission and a Novel Airborne Model Involving Inhalable Particles

Abstract

SUMMARY Since the beginning of the COVID-19 pandemic, there has been intense debate over SARS-CoV-2’s mode of transmission and appropriate personal protective equipment for health care workers in low-risk settings. The objective of this review is to identify and appraise the available evidence (clinical trials and laboratory studies on masks and respirators, epidemiological studies, and air sampling studies), clarify key concepts and necessary conditions for airborne transmission, and shed light on knowledge gaps in the field. We find that, except for aerosol-generating procedures, the overall data in support of airborne transmission—taken in its traditional definition (long-distance and respirable aerosols)—are weak, based predominantly on indirect and experimental rather than clinical or epidemiological evidence. Consequently, we propose a revised and broader definition of “airborne,” going beyond the current droplet and aerosol dichotomy and involving short-range inhalable particles, supported by data targeting the nose as the main viral receptor site. This new model better explains clinical observations, especially in the context of close and prolonged contacts between health care workers and patients, and reconciles seemingly contradictory data in the SARS-CoV-2 literature. The model also carries important implications for personal protective equipment and environmental controls, such as ventilation, in health care settings. However, further studies, especially clinical trials, are needed to complete the picture.

Positive no-touch surfaces and undetectable SARS-CoV-2 aerosols in long-term care facilities: An attempt to understand the contributing factors and the importance of timing in air sampling campaigns

“…The sample collection protocol in this work was guided by previous literature and expertise on the study of viral bioaerosols and on the very few published articles at the beginning of the pandemic 38 , 42 . To date, a consensus regarding a reproducible air sampling approach has not been reached even considering the various studies published to date 32 .…”

“…The level of contribution of the airborne route of transmission of SARS-CoV-2 is still to be defined and new models of a broader airborne model involving inhalable aerosols for SARS-CoV-2 transmission in low-risk health care settings is to be considered 32 . Cumulative data and positive air and no-touch surface samples found in healthcare facilities suggest that airborne transmission does not occur only for smaller aerosols, but that some larger particles normally classified as droplets can remain airborne and be transported inside building such as LTCFs 32 . In addition, contamination of no-touch surfaces likely involve larger particles or droplets given their ability to settle.…”

“…In addition, contamination of no-touch surfaces likely involve larger particles or droplets given their ability to settle. In that context, improper ventilation could contribute to viral accumulation in these environments 32 .…”

“…In addition, the contribution to viral aerosolization of common interventions in LCTF such as the use of continuous positive airway pressure (CPAP) machines or toilet flushing were not described in the COVID literature, nor was the impact of poor ventilation. All these limitations and differences in experimental approaches complexify interpretation and makes it difficult to generalize published knowledge to long-term-care facilities 32 . Nonetheless, these studies report positive air samples and no-touch surfaces in healthcare settings (≈8% to 100% positive) 31 , 33 , 34 , 35 , 36 , 37 , 38 , suggesting SARS-CoV-2 may be aerosolized in COVID-19 LCTFs.…”

Transmission and protection against re-infection in the ferret model with the SARS-CoV-2 USA-WA1/2020 reference isolate

“…The clinical manifestations of SARS-CoV-2 are referred to as coronavirus disease (COVID-19), and at the time of writing, SARS-CoV-2 has infected over 50 million people worldwide causing more than a 1.3 million deaths (5). Early during the pandemic, the mode of viral transmission was unclear; however, the growing consensus is large respiratory droplets are the predominant mode of transmission, with small droplets (sometimes referred to as “aerosol”) transmission also playing a role under certain environmental conditions (i.e., indoors with poor ventilation)(6).…”