The size distribution of SARS-CoV-2 genetic material in airborne particles sampled in hospital and home care environments occupied by COVID-19 positive subjects
Graphical abstract
Introduction
The dynamic of the COVID-19 pandemic is complex in terms of transmission pathways, infection risks and treatment approach. Despite of all efforts made by the medical experts and scientific community, many challenges remain unsolved in order to better understand epidemiology, pathology and transmission of COVID-19 (Dinoi et al., 2022, Domingo et al., 2020, Nazaroff, 2022, Tellier, 2022).
Expiratory human activities such as coughing, sneezing, and speaking generate a large size spectrum of respiratory particles which size can range from the sub-micrometric range to several hundreds of μm (Morawska et al., 2009; Nazaroff, 2022; Seminara et al., 2020; Shen et al., 2022; Stadnytskyi et al., 2021). The aerodynamic diameter is an important parameter for airborne particles since it can serve as a vector of pathogens which could be carried away by air currents or air jets well beyond the separation distance recommended during the current pandemic (2 m) (Bourouiba, 2020; Milton, 2020). The lifetime of particles in the air is heavily dependent on the size: fine (<2.5 μm) and especially sub-micrometric particles remain airborne for longer periods of time and may travel further than 2 m (Bahl et al., 2022).
A large body of evidence was reported on detection and different aspects of SARS-CoV-2 airborne transmission. First, SARS-CoV- 2 was reported to remain viable in the air for up to 3 h, with a half-life of 1.1 h, in laboratory experiments (van Doremalen et al., 2020). In other field studies, viable SARS-CoV-2 was detected in air samples collected in hospital wards and rooms occupied by COVID-19 patients (Lednicky et al., 2020; Santarpia et al., 2022). Numerous studies have detected SARS-CoV-2 RNA in airborne samples of total suspended particles (TSP) without size fractionation (Binder et al., 2020; Ding et al., 2021; Kenarkoohi et al., 2020; Lednicky et al., 2020; Razzini et al., 2020; Santarpia et al., 2020); whereas other studies collecting TSP did not detect the presence of any forms of SARS-CoV-2 RNA in samples (Cheng et al., 2020; Faridi et al., 2020; Liu et al., 2020; Masoumbeigi et al., 2020; Ong et al., 2020). Even though the evidence suggests that smaller respiratory particles, may be a vector for COVID-19 (Morawska and Cao, 2020; Morawska and Milton, 2020; Noorimotlagh et al., 2020; Stadnytskyi et al., 2020) and that the size of the particles containing pathogens impacts the likelihood of infection (Thomas, 2013), little is known about the size distribution of SARS-CoV-2 genetic material and its airborne transmission through different particle size fractions in indoor and outdoor air. Few studies consider size distribution in hospital environment: Liu et al. (2020) found SARS-CoV-2 in two size ranges (between 0.25 and 1.0 μm and >2.5 μm); del Real et al. (2022) in one size range (<2.5 μm); Santarpia et al. (2022) in three size ranges (<1 μm, 1–4 μm, and >4.1 μm); Chia et al. (2020) in two size ranges (1–4 μm and >4 μm); Stern et al., 2021b, Stern et al., 2022 in three size ranges (<2.5 μm, 2.5–10 μm, and >10 μm) and Oksanen et al. (2022) in six size ranges (0.65–4.7 μm, 7.0–12.0 μm, >10 μm, and <100 μm). All of these studies found SARS-CoV-2 RNA positive samples in multiple size fractions, however, they all report a rough size distribution (up to 6 size ranges), without detailed information on virus distribution in sub-micrometric particles.
Here we show for the first time the fine resolution of the size distribution of SARS-CoV-2 genetic material (originated from respiratory particles of COVID-19 positive patients) in airborne particles (down to the sub-micrometric size range) collected in different hospital and home care environments. Since there are still unanswered questions about the severity of risk of submicron particle-associated COVID-19 transmission and potential further infection, the evaluation of individual infection risk on the basis of hypothetical exposure scenario was also performed.
Section snippets
Study design, setting and participants
This study is an experimental investigation on the concentration and aerodynamic characteristics of size-segregated airborne particles containing SARS-CoV-2 genetic material in home care and different areas of hospital environment occupied with COVID-19 patients. Details about the patients in different environments studied can be found in SI Table 1. In order to collect proper amount of particles also in the sub-micrometric range, then allowing a proper RNA detection within, we decided adopting
Detection and quantification of SARS-CoV-2 genetic material
SARS-CoV-2 genetic material was detected at all investigated sampling sites (three hospital sites and one home care site). Positive qPCR results were detected in 10 out of 14 overall inspected particle size fractions (14), nine in 0.180–32 μm and one in 0.0180–0.032 μm size range. The genetic material was not found in the four (0.010–0.018, 0.032–0.180 μm) size fractions (Table 2). The broadest size distribution of SARS-CoV-2 genetic material was found in the MSW, where the genetic material was
Size distribution of SARS-CoV-2 genetic material in hospital and home care environments
The determination of the size of particles carrying viral RNA is critical to understanding their respiratory tract deposition, health impact, residence time in ambient air, and the potential for longer distance transport. Thus, the importance of different particle size contribution to the spread of COVID-19 is widely debated during the pandemic (e. g. Tang et al., 2021; Wang et al., 2021). However, the existing data are still scarce. A limited number of studies have presented size-resolved
Conclusions
The conducted study detected SARS-CoV-2 genetic material and determined its size distribution in airborne particles generated by infected subjects in hospital and home environments in order to carry out the assessment of the risk of infection, and generate data for future research. The SARS-CoV-2 genetic material was detected in all investigated sampling sites (three hospital sites and one home care site) throughout 71.4 % of investigated particle size fractions, nine ranging from 0.180 to
CRediT authorship contribution statement
Ana Cvitešić Kušan: Conceptualization, Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization, Project administration, Funding acquisition. Jurica Baranašić: Investigation, Formal analysis, Data curation, Writing – review & editing. Sanja Frka: Writing – original draft, Writing – review & editing, Visualization, Resources, Funding acquisition. Tomo Lucijanić: Writing – review & editing, Resources. Andrej Šribar: Writing – review &
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors specially acknowledge prof. Jasminka Peršec from University hospital Dubrava and School of Dental Medicine for her support in accessing the intensive care unit. The authors would like to thank Jadranka Škevin-Sović, Dipl. Ing, from the Croatian Meteorological and Hydrological Service for her efforts in granted concession for the use of the nanoMOUDI R122 instrument, acquired through the project “AIRQ - Expansion and Modernization of the National Network for Continuous Air Quality
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