The Covid-19 pandemic has seen three fundamental infection prevention and control (IPC) failures: an erroneous assumption of the mode of transmission; a failure to recommend respiratory protection equipment (RPE) for healthcare workers (HCWs) caring for people with Covid-19; and the mistaken assertion of equivalent efficacy between RPE and fluid resistant surgical face masks (FRSMs).
These failures have all happened in an era of evidence-based healthcare, and national and organisational guidance on this is still incorrect and unsafe.
Here I address these failures and provide evidence that: Covid-19 is airborne; HCWs caring for people with Covid-19 need RPE; and RPE provides greater protection than FRSMs. I do not discuss the consequences of these failures on the people who have been affected, rather my focus is on the need to change guidance. This is against the continuing backdrop of high Covid-19 infections and the risk of new variants as we move into autumn, and the high probability of future pandemics involving respiratory transmission of new and emerging pathogens.
“The UK still has no infection prevention guidance or evidence review that states Covid-19 is airborne”
The pre-Covid-19 pandemic paradigm of respiratory transmission was that pathogens enter to infect either via infectious droplets sprayed onto mucous membranes, or the inhalation of aerosols (Siegel et al, 2007). This paradigm defies physics (Marr and Tang, 2021).
Even in publications advocating the paradigm there were clear instances where outbreak data broke the paradigm’s rules. For example, in one SARS1 outbreak, the proximity of cases to the source suggested droplet transmission, but transmission far afield from the source could have been airborne (Wong et al 2004). Another SARS1 outbreak also demonstrated airborne transmission (Yu et al 2004). This led to a suggestion that some pathogens were either obligate, preferential, or opportunistically airborne (Roy and Milton, 2004). In hindsight, this was a failure to see that near-to-source-transmission could be airborne.
Aerosols are densest close to the source where they are inhaled; far afield transmission arises after their dispersal depending on air currents/ventilation. The paradigm also failed in terms of work-for-pandemic preparedness as influenza was identified as a pathogen that could be transmitted via both droplets and aerosols (Pandemic Influenza Preparedness Team, 2011). So, despite evidence that the ‘either airborne or droplet paradigm’ failed to fit some respiratory transmission, it did not result in reassessment.
Another flaw was an assumed cut-off point of 5µm in size that allegedly determined which pathogens were sprayed on and which were inhaled (Siegel et al, 2007). This also cannot be evidenced. It is accepted by aerobiologists that most of the gas cloud emitted when we exhale is made of small <5µm sized aerosols, most pathogens are in these aerosols, and most respiratory diseases are spread by the airborne route (Marr and Tang 2021; Fennelly, 2020).
Extant guidance erroneously considers that most respiratory infections are transmitted via droplets (NHS England and NHS Improvement, 2022). However, what broke the paradigm was an off-the-scale-infectious pathogen that brought largely non-infection control specialists to the fore to explain that the presentation of multiple separate Covid-19 outbreaks could only be explained by airborne transmission (Greenhalgh et al, 2021).
SARS-CoV-2 was and is airborne. Over a year into the Covid-19 pandemic, international public health bodies agreed, but the UK still has no infection prevention guidance or evidence review that states Covid-19 is airborne (NHS England and NHS Improvement, 2022).
The SARS1 outbreak identified that HCWs involved with aerosol generating procedures (AGPs) had a higher risk of nosocomial acquisition (World Health Organization, 2014). This is an association – not causation. Much work was done to establish which clinical procedures presented an aerosol-generating risk (Tran et al, 2011).
However, efforts in another direction – the production of aerosols during normal respiratory activity – countered the assertion that it was the AGP per se presenting the risk.
Oksanen et al (2021) showed there are more aerosols generated during coughing than during clinical AGPs. It is now proposed that the primary risk factors for nosocomial SARS-CoV-2 transmission are community incidence rates, viral load, symptoms, proximity, duration of exposure, and poor ventilation (Klompas et al, 2021a). Thus, the combination of aerosols being generated during normal respiratory activity and duration of time close to the infectious patient explains the association between AGPs and HCW acquisition (Klompas et al, 2021b).
However, without recognition of this closeness and duration risk, the list of AGPs necessitating HCWs to use RPE has been reduced (NHS England and NHS Improvement 2022). This is the worst of all outcomes, as this means HCWs are now at increased SARS-CoV-2 risk.
Recognising that during a pandemic the demand for RPE would rapidly deplete stockpiles, and as an alternative to solving supply issues, researchers evaluated infection prevention equivalency between RPE or the cheaper alternative FRSMs (Loeb et al, 2009). One examination of these endeavours stated that “All of these reviews, [of which there were 12] including a recent Cochrane review have surmised that there is inconclusive evidence to suggest that N95 respirators are superior to surgical masks when treating patients with predominantly droplet spread respiratory infections” (Antimicrobial Resistance and Healthcare Associated Infection (ARHAI) Scotland, 2021).
This statement contains erroneous assumptions of safety. First, the papers referred to in the review (and the reviewers) assume that the mode of transmission is droplets. Thus, the protocol would require mask use when close to a Covid-19 positive patient, rather than continuous use in a clinical area to protect against infectious airborne pathogens. Therefore, as droplet protocols would fail to protect HCWs against airborne pathogens, these studies were designed to fail to show benefit. One three-arm study of continuous mask use to prevent respiratory infections showed greatest benefit with RPE (MacIntyre et al, 2013).
Second, the Loeb et al (2009) study (the most frequently cited in all papers within the review) contains another error and a red flag. The error is a lack of controls. The trial compared RPE versus FRSMs against an assumed droplet pathogen and measured serological evidence of exposure to influenza over a season. As there were no controls, it is impossible to determine if the rate of influenza acquisition, which was equivalent in both arms, resulted from a failure of both masks or from both masks having the same impact.
The red flag was the positive serology rate of 23% in both arms – which appears high. Of note, another study found background influenza acquisition in HCWs who did not use masks over a season was also 23% (Elder et al, 1996).
FRSMs are neither classified as RPE, nor (with four leaky sides) designed to prevent virus inhalation. RPE has been shown to offer significantly greater protection in laboratory testing (Health and Safety Executive (HSE), 2008). And during the Covid-19 pandemic, one hospital’s change to RPE showed immediate benefit in reduced nosocomial cases (Ferris et al, 2021). Moreover, hospitals using RPE have been shown to have significantly fewer nosocomial Covid-19 cases than those using FRSMs (Lawton et al, 2022).
“The mistake here is not getting it wrong when the evidence is absent; rather it is not putting it right when the evidence is present”
Errors in outbreak management are to be expected; people at the beginning of an outbreak are working with incomplete evidence. The mistake here is not getting it wrong when the evidence is absent; rather it is not putting it right when the evidence is present.
I have demonstrated three fundamental pandemic failures all related to the erroneous interpretation of evidence. These relate to the mode of transmission, the precautions needed to protect against virus inhalation, and the efficacy of FRSMs versus RPEs. I have shown that SARS-CoV-2 is spread by aerosols, which are inhaled, HCWs need RPE when caring for infectious patients, and RPE is more efficacious than FRSMs against airborne pathogens. The failures I describe have resulted both in unsafe guidance and unsafe practice, and merit immediate rectification.
Dr Evonne Curran is honorary senior research fellow at the School of Health and Life Sciences, Glasgow Caledonian University
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