Modeling of nursing care-associated airborne transmission of SARS-CoV-2 in a real-world hospital setting

Abstract

Respiratory transmission of SARS-CoV-2 from one older patient to another by airborne mechanisms in hospital and nursing home settings represents an important health challenge during the COVID-19 pandemic. However, the factors that influence the concentration of respiratory droplets and aerosols that potentially contribute to hospital- and nursing care-associated transmission of SARS-CoV-2 are not well understood. To assess the effect of health care professional (HCP) and patient activity on size and concentration of airborne particles, an optical particle counter was placed (for 24 h) in the head position of an empty bed in the hospital room of a patient admitted from the nursing home with confirmed COVID-19. The type and duration of the activity, as well as the number of HCPs providing patient care, were recorded. Concentration changes associated with specific activities were determined, and airway deposition modeling was performed using these data. Thirty-one activities were recorded, and six representative ones were selected for deposition modeling, including patient's activities (coughing, movements, etc.), diagnostic and therapeutic interventions (e.g., diagnostic tests and drug administration), as well as nursing patient care (e.g., bedding and hygiene). The increase in particle concentration of all sizes was sensitive to the type of activity. Increases in supermicron particle concentration were associated with the number of HCPs (r = 0.66; p < 0.05) and the duration of activity (r = 0.82; p < 0.05), while submicron particles increased with all activities, mainly during the daytime. Based on simulations, the number of particles deposited in unit time was the highest in the acinar region, while deposition density rate (number/cm²/min) was the highest in the upper airways. In conclusion, even short periods of HCP-patient interaction and minimal patient activity in a hospital room or nursing home bedroom may significantly increase the concentration of submicron particles mainly depositing in the acinar regions, while mainly nursing activities increase the concentration of supermicron particles depositing in larger airways of the adjacent bed patient. Our data emphasize the need for effective interventions to limit hospital- and nursing care-associated transmission of SARS-CoV-2 and other respiratory pathogens (including viral pathogens, such as rhinoviruses, respiratory syncytial virus, influenza virus, parainfluenza virus and adenoviruses, and bacterial and fungal pathogens).

Keywords: Aerosol dispersion; Aerosol measurement; Airborne transmission; Elderly; Lung deposition; Nursing; SARS-CoV-2.

Fig. 1

The layout of the three-bed patient room. A Patient with COVID-19 confirmed with PCR test. B Optical particle counter located at the head position of an imagined patient. C Optical particle counter at the foot position of an imagined patient

Fig. 2

Time series of the measured number concentrations in two size bins, below 1 µm (orange curve) and above 1 µm (blue curve) with 1-min time resolution. The grey rectangles show the six selected events indicating the duration of the activities by their width

Fig. 3

Contributions on top of the baselines in the two size bins. The baselines are the concentrations preceding the events. The contributions were calculated by subtracting the baseline concentrations from the measured concentrations during the events

Fig. 4

Extrathoracic, bronchial, and acinar deposition density rates of the number of inhaled aerosol particles in the studied patient room. A All anatomical regions. B Extrathoracic airways. C Bronchial region. D Acinar region. Note the logarithmic vertical scale of the top-left summary plot. Calculated Pearson correlation coefficients with two-tailed test of significance: ♦r = 0.972, p < 0.05; ♣r = 0.977, p < 0.05; ♠r = 0.999, p < 0.05