When the air went viral: Exploring SARS-CoV-2 in aerosols during the covid-19 pandemic
Author
Summary, in English
Despite the enormous economic and health-related burdens caused by respiratory infectious diseases globally, there are significant knowledge gaps regarding how these are spread by aerosols. The covid-19 pandemic made it clear that understanding airborne transmission is especially important in healthcare, where workers and patients are highly exposed to sources of virus.
This thesis aims to advance the knowledge about airborne transmission of infectious diseases, mainly in hospital settings. More specifically, the objectives were to identify sources and risk factors for airborne virus, evaluate prevention strategies and explore the dynamics of infection via inhalation.
In total, we collected over 1100 air samples at hospitals during the covid-19 pandemic, both close to covid-19-patients and in other areas, such as ward corridors. The samples were analysed for SARS-CoV-2 RNA content to investigate presence and risk factors for airborne virus.
Overall, SARS-CoV-2 RNA was detected in around 10% of the samples collected close to patients. In corridors and anterooms, less than 5% of the air samples contained SARS-CoV-2. Interestingly, almost half of the aerosols containing SARS-CoV-2 in corridors were of submicron size. SARS-CoV-2 was also found on surfaces that are less likely contaminated by touch, but rather by airborne transport.
A number of factors significantly increased the risk of detecting airborne virus in patient rooms: smaller distance to the patient, lower ventilation rates in the room, and higher viral load of the patient, which correlated with the number of days since symptom onset. Certain medical procedures, called aerosol-generating procedures, were hypothesized to spread more aerosols. Our results indicated that aerosol-generating procedures are of lesser importance, although with a few exceptions. SARS-CoV-2 was found during both childbirth and autopsy, but with no clear risk factors.
To further understand aerosol transmission dynamics, exhaled virus from newly infected subjects was analysed for viability. This allowed us to model the emissions of infectious virus from a source in a typical office size room. The simulations showed that a susceptible person can inhale one infectious dose within minutes upon entering a room with an infected individual. The time until infection varied strongly with the individual emission rate of the source. When modelling a scenario of a patient room with a higher ventilation rate, it was found that ventilation rate had some effect on the time, especially for lower emission rates, but again the most important factor was the individual emission rate. This underlines the large individual variations and how important they are for disease spread.
In conclusion, this work contributes to increased knowledge about sources of airborne virus, risk factors and prevention strategies. Our results support the importance of airborne SARS-CoV-2 in transmission of covid-19, but also highlight the challenges of predicting risk situations and designing effective mitigation strategies. Importantly for indoor environments, the risk of infection is smaller with increased ventilation and distancing to the source. Moreover, transmission dynamics are likely highly dependent on individual variations in viral emissions.
This thesis aims to advance the knowledge about airborne transmission of infectious diseases, mainly in hospital settings. More specifically, the objectives were to identify sources and risk factors for airborne virus, evaluate prevention strategies and explore the dynamics of infection via inhalation.
In total, we collected over 1100 air samples at hospitals during the covid-19 pandemic, both close to covid-19-patients and in other areas, such as ward corridors. The samples were analysed for SARS-CoV-2 RNA content to investigate presence and risk factors for airborne virus.
Overall, SARS-CoV-2 RNA was detected in around 10% of the samples collected close to patients. In corridors and anterooms, less than 5% of the air samples contained SARS-CoV-2. Interestingly, almost half of the aerosols containing SARS-CoV-2 in corridors were of submicron size. SARS-CoV-2 was also found on surfaces that are less likely contaminated by touch, but rather by airborne transport.
A number of factors significantly increased the risk of detecting airborne virus in patient rooms: smaller distance to the patient, lower ventilation rates in the room, and higher viral load of the patient, which correlated with the number of days since symptom onset. Certain medical procedures, called aerosol-generating procedures, were hypothesized to spread more aerosols. Our results indicated that aerosol-generating procedures are of lesser importance, although with a few exceptions. SARS-CoV-2 was found during both childbirth and autopsy, but with no clear risk factors.
To further understand aerosol transmission dynamics, exhaled virus from newly infected subjects was analysed for viability. This allowed us to model the emissions of infectious virus from a source in a typical office size room. The simulations showed that a susceptible person can inhale one infectious dose within minutes upon entering a room with an infected individual. The time until infection varied strongly with the individual emission rate of the source. When modelling a scenario of a patient room with a higher ventilation rate, it was found that ventilation rate had some effect on the time, especially for lower emission rates, but again the most important factor was the individual emission rate. This underlines the large individual variations and how important they are for disease spread.
In conclusion, this work contributes to increased knowledge about sources of airborne virus, risk factors and prevention strategies. Our results support the importance of airborne SARS-CoV-2 in transmission of covid-19, but also highlight the challenges of predicting risk situations and designing effective mitigation strategies. Importantly for indoor environments, the risk of infection is smaller with increased ventilation and distancing to the source. Moreover, transmission dynamics are likely highly dependent on individual variations in viral emissions.
Department/s
Publishing year
2024-04-26
Language
English
Full text
Document type
Dissertation
Publisher
Department of Design Sciences, Faculty of Engineering, Lund University
Topic
- Other Medical Sciences
- Other Engineering and Technologies
Status
Published
ISBN/ISSN/Other
- ISBN: 978-91-8104-054-8
- ISBN: 978-91-8104-055-5
Defence date
24 May 2024
Defence time
09:15
Defence place
Lecture hall Stora Hörsalen, Ingvar Kamprad Designcentrum (IKDC), Sölvegatan 26, Faculty of Engineering LTH, Lund University, Lund
Opponent
- Digby Warner (Prof.)