Fig 1.
Timeline of confirmed COVID-19 cases in Santander from March 2020 through October 2021.
Fig 2.
Plan view of one of the floors of the multi-family housing building in Santander (a), and vertical diagram of the natural ventilation opening of the bathroom and the duct that connects to the roof (b).
There are four homes on each floor, grouped two by two around four patios. The red box represents the affected homes and patio that share the same vertical bathroom ventilation duct.
Fig 3.
Side and three-dimensional view of the Santander building.
The index cases were on the 3rd floor-Home A (dark red), testing positive on Jun 21, 2020. Subsequent infections (light red) occurred on floor 1-Home B, floor 4-Home A, and floor 6-Home A. Letters A and B indicate that the infection occurred in Home A or Home B on that floor. Homes A and B shared a vertical bathroom duct and patio area. The other 10 homes sharing the vertical bathroom duct were either inhabited or not occupied, or their bathroom duct was modified, and no infection was documented.
Fig 4.
Maximum likelihood phylogenetic tree obtained from complete genome sequences of SARS-CoV-2.
Sequences derived from samples of inhabitants with COVID-19 in the Santander building outbreak are labeled COV007081, COV007082, and COV007085 and marked with a red dot. The Wuhan-1 sequence is labeled as MN908947.3. The remaining sequences correspond to local controls from Santander taken in June and July 2020. Bootstrap support values higher than 70% are shown in the corresponding nodes. The scale bar represents inferred substitutions/site.
Table 1.
Measurements Conducted in the 4th Floor Apartment of the Santander Building in 2022.
Fig 5.
Schematic representation of the CFD model geometry (dimensions in millimeters) used to model two vertically aligned, adjoining bathrooms.
Table 2.
Boundary Conditions for the Simulated Conditions.
Table 3.
Comparison of CFD Simulated Airflow Rates and Carbon Dioxide Concentrations with Measurements.
Fig 6.
Air velocities in the central plane of the bathroom ventilation duct for patio window open.
Fig 7.
CO₂ concentrations in the central plane of the bathroom ventilation duct for patio window open.
Fig 8.
Air velocities in the central plane of the bathroom ventilation duct for kitchen exhaust hood on.
Fig 9.
CO₂ concentrations in the central plane of the bathroom ventilation duct for kitchen exhaust hood on.
Fig 10.
CONTAM-Quanta model for the Santander residential building, Northern Spain.
The building is shown in (a), and the floor plan of each floor is outlined in (b), with the gray area indicating Home A, which is where the infected residents lived on the 3rd floor. The index cases were located on the 3rd floor, specifically in Home A (Rooms A and Bath A). Simulations were conducted exploring the impacts of outdoor wind, window opening, and bathroom fan and kitchen operation on airborne infection.
Table 4.
Cases Investigated with the CONTAM-Quanta Model*.
Fig 11.
Comparison between CONTAM Model simulated airflows and 4th Floor bathroom Santander building field measurements.
The flow rate time profile is shown in (a), and the correlation between model and measurements is in (b).
Fig 12.
Schematics showing quanta concentrations for CONTAM-Quanta simulation Cases 1–4 on different floors of the building and in different rooms.
The index cases were located on the 3rd floor, Home A. Five infected individuals were in Room A, and one infected individual was in Bath A on level 3. The white color indicates zero quanta concentration, the dark green color is 0.03-0.11 quanta/m3, and the red color is 2.0-8.6 quanta/m3.
Fig 13.
Schematics showing quanta concentrations for CONTAM-Quanta simulation Cases 5 and 6 on different floors of the building and in different rooms.
The white color indicates zero quanta concentration, the dark green color is 0.03-0.11 quanta/m3, and the red color is 2.0-8.5 quanta/m3. Five infected individuals were in Room A, and one infected individual was in Bath A, on level 3.
Fig 14.
Probability of infection on the 2nd, 3rd, and 4th floors for every room that was simulated in the CONTAM model.
Panels (a) through (f) correspond to wind and weather simulation Cases 1 through 6. Five infected individuals were in Room A, and one infected individual was in Bath A, on the 3rd floor.
Fig 15.
Schematics showing quanta concentrations for CONTAM simulation Cases 7-9 on different floors of the building and in different rooms.
The white color indicates zero quanta concentration, the dark green color is 0.03-0.11 quanta/m3, and the red color is 2.0-8.5 quanta/m3. Five infected individuals were in Room A, and one infected individual was in Bath A, on level 3.
Fig 16.
Probability of infection on the 2nd, 3rd, and 4th floors.
Panels (a) through (c) correspond to window opening Cases 7 through 9. Five infected individuals were in Room A, and one infected individual was in Bath A, on the 3rd floor.
Fig 17.
Schematics showing quanta concentrations for CONTAM simulation Cases 10–12 on different floors of the building and in different rooms.
The white color indicates zero quanta concentration, the dark green color is 0.03-0.11 quanta/m3, and the red color is 2.0-8.5 quanta/m3. Five infected individuals were in Room A, and one infected individual was in Bath A, on level 3.
Fig 18.
Probability of infection on the 2nd, 3rd, and 4th floors.
Panels (a) through (c) correspond to Bathroom fan simulations Cases 10 through 12. Five infected individuals were in Room A, and one infected individual was in Bath A, on the 3rd floor.
Fig 19.
Schematics showing quanta concentrations for CONTAM simulation Cases 13–15 on different floors of the building and in different rooms.
The white color indicates zero quanta concentration, the dark green color is 0.02-0.10 quanta/m3, and the red color is 1.8-8.0 quanta/m3. Five infected individuals were in Room A, and one infected individual was in Bath A on level 3.
Fig 20.
Probability of infection on the 2nd, 3rd, and 4th floors.
Panels (a) through (c) correspond to kitchen exhaust Cases 13 through 15. Five infected individuals were in Room A, and one infected individual was in Bath A, on the 3rd floor.