Ventilation with fresh outdoor air has recently gained considerable attention as a means to reduce the potential risk of indoor aerosol transmission of respiratory pathogens such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus causing coronavirus disease 2019 (COVID-19). Commercial carbon dioxide (CO2) monitors are increasingly used in schools, long-term care facilities, offices and public buildings to monitor indoor ventilation. However, no formal evidence is available to support the effectiveness of feedback from CO2 monitoring devices. Moreover, modern hospitals have superior indoor air quality control systems.

The aim of this prospective pilot randomized controlled trial (RCT) is to evaluate whether CO2 monitoring devices would be useful as a means to further maintain lower indoor CO2 concentrations in hospitals.

In this pilot, randomized, sham-controlled open-label RCT, hospital rooms will be fitted with Aranet4 Home CO2 sensors.

Each device will continuously measure indoor CO2 concentrations at 1-minute intervals during 4 time periods:

1. Baseline: staff blinded to CO2 levels displayed on sensor

2-3. Sham/Intervention period: sensors on the same ward will be randomized to placebo (sensor not showing CO2 levels to staff) or Intervention (sensor displaying CO2 levels to staff) in a cross-over design

4. Post-intervention phase (3 weeks post-intervention): staff blinded to CO2 levels

Each measurement period will consist of 7 days with no washout period.

Our primary hypothesis is that CO2 sensors will record less time (minutes) with elevated CO2 levels during the intervention period, compared to the Sham periods. However, carry-over effects will be investigated by comparing the Intervention periods to the Baseline and Post-intervention phases.

Note [February 27, 2021]: due to technical problems with the Aranet4 device Bluetooth connection, outcome data will be analyzed according to measurement data at 2-5 minute intervals (measurements can be made every minute, but data cannot be downloaded with the current version of the app due to technical problems).

Inclusion Criteria:

• Double-bed hospital rooms

Exclusion Criteria:

• Unoccupied rooms

When applicable, patients stay in double-bed rooms based on gender.

The full set of sensor data will be made available to established investigators upon simple request.

Data will be available upon fulltext print publication in a peer-reviewed journal, for a duration of at least 10 years.

Simple e-mail request to the corresponding author by an established scientific investigator