Characterization of simulated cough with virus bioaerosol and evaluation of face shields for controlling inhalation exposure
Creators: name: Pratt, Alessandra
Publisher: name: University of Iowa
Year: 2024
Subjects: Bioaerosol
Cough
Exposure
Healthcare
Virus
Worker Safety
Occupational safety
public abstract

description: 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.
description: 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&lt;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.
description: 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 &gt; 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&lt;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.