CO₂ Monitoring to Spot Airborne Illness in Hospitals

Shoubridge, A. P. et al., (2025) summarised by Amanda Harrington-Vail

Introduction

Hospitals have strategies for infection control person to person, in the air and on surfaces. The COVID-19 pandemic identifies the specific need to control airborne infection. Use of facemasks, social distancing and reduced in-person outpatient clinical services demonstrated substantial decreases in respiratory infection rates, that are spread by airborne transmission. Although it has long been argued that increased rates of air exchange are effective in reducing airborne transmission in hospitals, the associated heating and cooling costs can be prohibitive. However inexpensive carbon dioxide (CO₂) monitors can be used to swiftly survey large indoor facilities to identify areas of high airborne transmission risk. CO₂ is exhaled through human breath, its concentration indicates levels of occupancy and ventilation. Elevated CO₂ levels are widely used as a marker of indoor air quality and as a basis for assessing air exchange and ventilation efficiency. Low air quality relates to high transmission of airborne illness. This research took place in a hospital that provides advanced medical procedures for specialist care in South Australia.

Summary

The study focused on nonclinical areas, which typically have less stringent infection control measures than clinical areas. Air samplers were disinfected before use and placed as recommended by the American Society of Heating, Refrigerating and Air- Conditioning Engineers. Air quality was assessed remotely using wall-mounted CO₂ sensors, they were not placed near doors, windows or ventilation ducts and multiple sensors were used in large spaces. The assessed areas were:

• Hospital main entrance
• Waiting areas for: women’s health; outpatient clinic; ultrasound; medicine clinic; emergency department; cancer treatment clinic; rehabilitation clinic
• Staff areas: tearooms; student rooms; shared staff offices; consulting rooms

16 zones were assessed and only 1 had CO₂ levels that consistently exceeded the threshold. It was the waiting area for women’s health with its outpatient clinics for antenatal, midwifery, obstetrics and gynaecology. The area had 3 staff members, seating for 45 people and 12 adjoining examination rooms. As the area had no external walls it was not possible to remedy the excessive CO₂ levels by installing a simple ventilation appliance, and clinicians did not favour the rescheduling of appointments to stagger visitor arrival. However, resetting the sites heating, ventilation and air conditioning (HVAC) system resulted in CO₂ levels decreasing to acceptable levels.

Conclusion

Research findings highlight the importance of assessing nonclinical areas and ensuring the use of HVAC systems are monitored for their effectiveness. In hospitals, and other medical settings, it is the waiting area that has the highest occupancy and turnover of visitors. CO₂ monitors easily identify risk areas, these areas should be targeted to improve air quality, which will reduce transmission of airborne illness to increase staff and visitor wellbeing.

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