Health Systems Action

Hospital-acquired Covid-19. The HAI we ignore, but can fix, by taking a CAB

In England, two and a half years into the global pandemic, a third of patients hospitalised with Covid acquire it in the hospital. What’s going on?!

Hospital-acquired Covid in England – updated 20th October 2022 – in 28 days, 11,234 of 30,439 people in hospital with Covid probably or definitely caught it there (36.9%).

The variation is huge across hospitals – as low as 7.5%, all the way up to 80%.

Prevention of healthcare-associated infection (HAI) (also known as hospital-acquired infection) has been at the core of patient safety for decades. Consequently, it’s no longer acceptable for patients to acquire an infection during a routine hospital admission, though many still do, especially in low- and middle-income countries (LMICs).

Scaled up quality improvement initiatives over the last 15-20 years, including in SA, showed that serious infections, like those associated with invasive devices like central lines (drips inserted into large blood vessels in the chest), for example, could decline to almost zero over sustained periods even in busy ICUs caring for very sick patients. Care bundles and a culture of safety do the trick.

How then is it acceptable, in this “controlled” phase of the Covid-19 pandemic, for 30% of documented Covid infections to be hospital-acquired? 

Would the high numbers in most English hospitals be different to rates in SA or anywhere else? The huge extent of variation across hospitals, in a country where every town and village has seen the Covid pandemic pass through, suggests that local hospital factors are important.

What is the mechanism of disease transmission? Are these infections spread by staff or patients? Does hand hygiene help?

The mechanism is airborne, the medium is air. Viruses are breathed out, carried by small particles that float, by patients or staff who are, mostly, not coughing or sneezing, in spaces with poor ventilation.

Hand hygiene is critical for preventing other HAIs but has little or no impact on prevention of Covid. Or TB, for that matter.

Staff working in special TB hospitals, caring for patients harboring the nastiest airborne pathogen, seldom get TB. TB hospitals pay special attention to ventilating all their indoor spaces, and staff wear properly fitted, high quality masks. No hazmat suits and no special surface antisepsis.

What about staff who acquire Covid in hospital, during the course of a normal working day? How does this happen?

The early pandemic concept of the “aerosol-generating procedure” – putting tubes in and other procedures on the airway of patients with Covid being the highest risk thing for people to do – turns out to be the wrong idea (see Bibliography below). Covid, and probably TB, is transmitted mostly by people breathing and talking, indoors, close up, in poorly ventilated spaces; often they are asymptomatic spreaders. Nurses working in regular wards, not ICUs are at higher risk than anaesthetists. 

Hospitals most places are short of personnel. In this post-pandemic period, Covid and other preventable infections exacerbate the pressure, creating risk for patients and more stress on staff. Amidst staff shortages, there’s a compulsion to attend work even when ill, thereby worsening the risk of disease for everyone else, staff and patients, in hospital wards containing include our most vulnerable.

In the setting of a moribund vaccination campaign, and ongoing viral mutation with immune escape, this spells trouble.

It’s not only about Covid. As noted, Covid’s airborne mechanism of spread is how not only tuberculosis, but influenza and RSV are transmitted too. As Covid testing slows, and mitigations are abandoned, other viral illnesses surge, their impact on the health system becoming indistinguishable in severity from Covid-19.

Interesting studies in Cambridge suggest that even bacterial infections that cause problems like wound infections may be airborne also. These bacteria can be sampled from air, and their concentration can be reduced by air filtration devices positioned strategically in hospital wards.

An appropriate response to rising rates of illness caused by respiratory pathogens would be to test and spread evidence-based interventions that can reduce all forms or airborne disease transmission in hospital wards and other clinical areas, including primary care clinics and GP waiting rooms. I propose the Clean Air Bundle (CAB).

1.    Check and improve the ventilation in all occupied indoor spaces. Various tools, including CO2 meters, are available for this task; occupational health and industrial hygiene experts do the work routinely. Good ventilation dilutes levels of airborne germs, even up close to infected persons (up to a metre or two), significantly reducing risk for everyone, patients and staff.

2.    Filter the air – the cost is down, availability up; HEPA and MERV-13 filters can be built into central ventilation (“HVAC”) systems and portable ones.

3.    Ultraviolet (UV) light technology is newer, with increasing evidence of efficacy; devices can be placed at the upper level of rooms with good circulation of air so bugs float up, get irradiated and die; people are not harmed.

4.    Staff who are sick get tested and stay home; R50 Covid self-testing kits are now licensed and available; tests for flu and other viral illness may be on the way.

5.    Last but not least, masks. We got used to them but have now given them up. When infection rates, and hospital admissions are high, we need to go back to them. Staff and patients. Furthermore, we need to be reminded that any mask worn on the chin is not protective, it is pure ritual. High quality masks have to be worn properly.

Bundle item #5 is the hardest to implement. Preferred interventions are those that rely least on behavioural change. Clean the air! Take a CAB!

PS Where’s vaccination? Vaccination protects individuals and populations but no longer significantly limits the spread of transmission. Still recommended but not in the CAB!

Article updated: November 29, 2022 07:47


Brown J, Gregson FKA, Shrimpton A, et al.  A quantitative evaluation of aerosol generation during tracheal intubation and extubation. Anaesthesia 2021; 76: 174–81.

Shrimpton AJ, Brown JM, Gregson FKA, et al. Quantitative evaluation of aerosol generation during manual facemask ventilation. Anaesthesia 2022; 77: 22–7.

Shrimpton AJ, Gregson FKA, Brown JM, et al. A quantitative evaluation of aerosol generation during supraglottic airway insertion and removal. Anaesthesia 2021; 76: 1577–84.

Wilson NM, Marks GB, Eckhardt A, et al. The effect of respiratory activity, non-invasive respiratory support and facemasks on aerosol generation and its relevance to COVID-19. Anaesthesia 2021; 76: 1465–74.

Hamilton FW, Gregson FKA, Arnold DT, et al. Aerosol emission from the respiratory tract: an analysis of aerosol generation from oxygen delivery systems. Thorax 2021; 77: 276–82.

Shrimpton A, Brown J, Cook T, et al. A quantitative evaluation of aerosol generation from upper airway suctioning during tracheal intubation and extubation sequences. Journal of Hospital Infection 2022; 124: 12–21.

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top