Overview
- Researchers report in PLOS One that a shared vertical bathroom duct was the most plausible transmission route in a 2020 Santander outbreak that sickened 15 residents across four stacked flats.
- Investigators linked cases by genome sequencing and detected high breath-derived CO2 in a vacant unit, showing air from occupied apartments moved through the common shaft.
- Airflow tests and computer modeling found that weather shifts and kitchen exhaust hoods can flip or speed flow, pulling bathroom air from one home into another within minutes.
- The authors call for updates to building standards for older high-rises and recommend low-cost steps such as adding exhaust fans with backdraft flaps to block incoming air.
- The shaft design was phased out in Spain in 1975 yet remains in many older buildings worldwide, and researchers note similar cross-room spread has been observed in hotels.