Dissertation
Characterization of simulated cough with virus bioaerosol and evaluation of face shields for controlling inhalation exposure
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2022
DOI: 10.25820/etd.007230
Abstract
Healthcare workers are exposed to SARS-CoV-2 when treating COVID-19 patients. Over 350,000 healthcare workers (HCWs) in the United States have contracted COVID-19 since November 2019, demonstrating a burden of disease among workers in healthcare. Virus aerosol exposure is considered one of the primary routes of transmission of SARS-CoV-2. Coughing is a primary symptom of COVID-19 and a source of SARS-CoV-2 aerosol. Therefore, there is an urgent need to understand how SARS-CoV-2 can be transmitted through coughing, as well as evaluating control strategies to reduce exposure to healthcare workers and other patients. Our central hypothesis is an aerosolized virus, through coughing, is a significant source of exposure for healthcare workers and controlling aerosol generation is essential to reducing exposure and therefore reducing the risk of infection. In the first study, we developed a prototype machine to simulate human coughing to conduct experiments on exposure and exposure control of aerosolized virus (e.g., SARS-CoV-2). The “coughing machine” operates by exhaling a volume of air through the mouth of a mannequin that contains aerosolized virus to simulate a human cough. We used a spirometer to compare the simulated cough to published characteristics of a human cough. We aerosolized ultraviolet reactive dye using the coughing machine to visualize and photograph the simulated cough. We also characterized the aerosols generated by the cough at 0.41 meters (m) and 1.8 m (sixteen (16) inches and six (6) feet) using two optical particle counters. The distances were chosen because they represent the distances a HCW may be from infected patient when they are exposed to cough. We successfully generated a simulated cough with a similar flow rate to a human cough. We generated a plume with the coughing machine that is similar in shape to a human cough. We also characterized aerosols generated from the coughing machine and found that increasing the distance an HCW stands from a patient (from 16 inches to 6 feet) does not significantly change the amount of particles they are potentially exposed to across the particle sizes measured. Our observations suggest that we have successfully created a simulated cough containing live virus using our prototype coughing machine. Our plan is to use the coughing machine to study virus aerosol transmission dynamics in healthcare environments.
In the second study, we compared virus aerosol particle concentrations across a face shield, worn on an HCW, during a simulated patient cough. The bacteriophage, MS2, was used as a surrogate virus for SARS-CoV-2 and was aerosolized using the coughing machine. An impinger sampler, the SKC Biosampler, was used to collect the aerosolized MS2 in front of and behind a face shield worn by a simulated HCW exposed to a patient cough. A double layer plaque assay was used to determine the concentration of viable virus. GRIMM 11-D optical particle counters were used to measure the airborne number concentration across 1-second time intervals on both sides of the face shield. We found that the face shield significantly reduced the virus concentration (p<0.01), however viable virus was observed in the breathing zone of the simulated HCW. There was a significant difference in number particle concentration across the face shield for most particle sizes (i.e., channel size) measured, however not all channel sizes were significantly different across the face shield. These results suggest that a face shield does not adequately protect HCWs from aerosols generated from a coughing patient and additional PPE should be used. A face shield is still effective as a barrier protection device (i.e., prevent from splatter and sprays as well as reduce HCW touching eyes, nose, and mouth) although based on our observations, did not eliminate viable virus concentrations in the breathing zone of the HCW.
In the third study, we evaluated two types of face shields, placed on a simulated coughing patient, for reducing virus aerosol exposure to HCWs. The two face shields, a typical disposable plastic face shield and a novel negative pressure face shield (NPFS), were designed to be used during scope procedures at the Otolaryngology clinic at the University of Iowa Hospitals and Clinics. The NPFS is designed to evacuate potentially contaminated air away from the breathing zone of the HCW before HCW exposure. The SKC Biosamplers and GRIMM 11D OPCs were placed on the inside of the face shields (i.e., near the mouth of the coughing machine mannequin) and 0.41 meters from the cough which is where an HCW would be when performing a laryngoscopy scope procedure. We observed that when the simulated coughing patient wore the disposable plastic face mask and the NPFS was set to a low flow rate [e.g., 10 Liters Per Minute (LPM)] there was no significant difference in virus concentration across the NPFS, therefore potentially exposing the HCW (p > 0.05). However, when the flow rate of the NPFS was increased (i.e., 38.6 LPM) there was a significant reduction in viable virus concentration as well as particle concentration (p<0.05). These results indicate that the NPFS face shield, when used at a flow rate of 38.6 LPM, can effectively reduce viable virus and aerosol particle concentrations, therefore reducing HCW exposure to during laryngoscopy procedures.
Details
- Title: Subtitle
- Characterization of simulated cough with virus bioaerosol and evaluation of face shields for controlling inhalation exposure
- Creators
- Alessandra Pratt
- Contributors
- Matthew W Nonnenmann (Advisor)Kelly K Baker (Committee Member)Grant D Brown (Committee Member)Aloysius J Klingelhutz (Committee Member)Philip Polgreen (Committee Member)Jarrett Walsh (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Occupational and Environmental Health
- Date degree season
- Summer 2022
- DOI
- 10.25820/etd.007230
- Publisher
- University of Iowa
- Number of pages
- xvi, 121 pages
- Copyright
- Copyright 2022 Alessandra Pratt
- Grant note
- Thank you also to the Heartland Center for Occupational Safety and Health, NIOSH, and the CDC for funding my research or me.
- Language
- English
- Date submitted
- 07/25/2022
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references (pages 101-118).
- Public Abstract (ETD)
Severe Acute Respiratory Syndrome (i.e., the COVID-19 virus) spreads throughout the air. Healthcare workers (HCWs) are exposed to the virus when they are treating sick patients that cough. A coughing machine was developed to mimic a sick patient and study how HCWs might get infected. The first analysis of the coughing machine examined how well the coughing machine compared to a human cough and how increasing distance from a patient’s cough may affect exposure. It was found that the coughing machine was very similar to a patient cough and that with increasing distance away from the cough there may be some protection to an HCW, but it is not fully protective and other control measures need to be used. The second analysis looked at how effective a face shield is a preventing exposure when an HCW wears it. The results were that an HCW, wearing a face shield, is not protected from exposure when they are near the cough. The third analysis examined how effective two different types of face shields are at reducing exposure to HCWs when a coughing patient wears them. One face shield type that was tested was a typical disposable plastic face shield and the other was a negative pressure face shield (NPFS). The NPFS is designed to evacuate potentially contaminated air away from the patients face before it can expose HCWs. What was found was that the NPFS, when evacuating a high amount of air, was very protective and no virus was found where the HCW is.
- Academic Unit
- Occupational and Environmental Health
- Record Identifier
- 9984454645002771
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