You may have seen some commentary and debate on a recently updated Cochrane review on physical interventions to interrupt the spread of respiratory viruses. I’m stepping into the debate only to clarify a few small points – and to provide an overview of what the review does (and does not) tell us. However, my firm advice is to read the review for yourself and come to your own conclusions.
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Face coverings, surgical masks, and face filtering piece (FFP) respirators: what’s the difference and how are they tested?
You’ll all have seen wide variety of masks and face coverings worn in a wide (and often alarming!) variety of ways. Leaving aside the (in)correct wearing of masks, it’s useful to see some comparative data on the relative respiratory protection offered by different mask materials. This study, published years ago (pre COVID!), does just that.
COVID-19 & PPE / face coverings / masks / shields: personal safety depends on more than what you wear
There’s a huge amount of academic and pragmatic discussion and debate about the appropriate levels of PPE to wear in various healthcare settings to reduce the risk of spreading COVID-19 to yourself and others in healthcare settings. And more recently, when to wear face coverings / masks / shields in public areas of hospitals, on public transport, and in shops. However, there is much, much less discussion about the importance of careful doffing (removal) of PPE and face coverings etc in order to ensure the safe and effective use of PPE. This helpful Cochrane Review, updated for the COVID-19 era, covers a lot of ground and one key conclusion is that doffing is key: if it is done carefully, the risk of self-contamination is lower.
PPE for preventing highly infectious diseases
The use of PPE and the protection of HCWs against highly infectious diseases was (and is) a topic of major importance, around the globe. The recent Cochrane review by Verbeek et al. was probably hoping to offer this “vital” information.
Unfortunately, they found no studies on the effects of goggles, face shields, long-sleeved gloves or taping on the risk of contamination. All they found was very low quality evidence, with high risk of bias and uncertain estimates of effect, that:
- More breathable types of PPE offer more comfort without increasing the risk of contamination
- Double gloving and CDC doffing guidance appear to decrease the risk of contamination, and
- Active more than passive training in PPE use may reduce PPE and doffing errors.
Their conclusions are obvious: we need high-quality studies of the materials, their use and protective effects, safe ways of doffing, and the most adequate training to achieve safe use of PPE for HCWs in the presence of highly infectious diseases or those (even less infectious) that may cause severe harm to HCWs.
But what to do until than? My personal opinion is that we should only use PPE, we are used to and know how to use. First-time users, even if supplied with the best available products, will inevitably fail to remove the PPE without error. Consequently, institutions should have a stable selection of PPE, and in the case of preventing highly infectious diseases, a selected group of HCWs with continuous active training, as it is too late to start when the next epidemic is hitting our healthcare centers.
MERS-CoV: a survival guide for you and your patients
This time last week, we were on red alert that a MERS-CoV pandemic was gathering pace. The news over the last few days has been more encouraging, with no new cases reported in Saudi Arabia, the epicenter of the MERS-CoV cases. However, there are still plenty of patients with MERS-CoV who need to be cared for around the world. Like SARS-CoV, but unlike the “usual suspects” that cause HCAI such as MRSA and C. difficile, MERS-CoV has the capacity to affect both healthcare workers and patients. Thus, I hope that this ‘survival guide’ will prove useful to those on the front line.
I presented a webinar on ‘MERS-CoV: coming to a hospital near you? Infection prevention and control challenges’. You can download the slides here. I came across a fantastic blog whilst preparing the webinar: ‘Virology Down Under’ by Dr Ian Mackay. I’ve used some of his excellent images in the slides, with his kind permission.
There are two transmission routes to consider for MERS-CoV: droplet / aerosol and contact / fomite. CDC recommends both airborne and contact isolation procedures to reflect these transmission routes. This involves placement of the patient in a negative pressure airborne infection isolation room, and the use of gloves, gowns, eye protection and N95 (FFP3) mask, and, of course, hand hygiene. PHE recommends a similar approach.
First and foremost, as a respiratory virus, inhalation of infected droplets is likely to be the most important transmission route. However, whilst not an ‘airborne’ virus (such as measles), aerosols can be generated by MERS-CoV patients that comprise small droplet nuclei that travel for long distances. A recent study of influenza suggests that the generation of aerosols is surprisingly common, to the extent that ‘living and breathing is an aerosol generating procedure’. Indeed, a recent study showed that a MERS-CoV aerosol diminished by only 7% over 10 minutes (compared with 95% for influenza). The use of an N95 (FFP3) mask will prevent direct inhalation of droplets / aerosols, and gloves, gowns and eye protection will prevent contact with mucous membranes and contamination of clothing or hands for subsequent nasal inoculation. But, if MERS-CoV aerosol is generated in the patient’s room (which seems likely), how long will it last and will the subsequent admission to the next room be at risk?
Let’s assume a patient sheds a MERS-CoV infectious aerosol of 6-log. I’m not aware of any infectious dose data for MERS-CoV yet, but for SARS-CoV it can be as low as <20 plaque forming units. Given the decay rate of 7% over 10 minutes, infectious aerosol above the infectious dose could be present after the discharge of the patient for a little under 26 hours! Even if the virus was shed at a lower titre, infectious aerosol times would still be considerable (Table). Could this be a job for automated room disinfection systems, which address both surface and airborne contamination? One such system, hydrogen peroxide vapour, has recently been shown to inactivate the SARS-CoV surrogate, TGEV.
| Shed titre | Time to reach 20 virus particles |
| 1000000 | 26 hours |
| 100000 | 20 hours |
| 10000 | 15 hours |
| 1000 | 9 hours |
| 100 | 4 hours |
Table: Relationship between shed titre of MERS-CoV and time to reach 20 virus particles.
Whilst respiratory viruses are not that great at surviving on surfaces compared with C. difficile spores and some vegetative bacteria, they can survive long enough to bring contact / fomite transmission into play. A number of reviews have concluded that contact / fomite transmission is an important route for influenza and other respiratory viruses such as rhinovirus. The SARS-CoV and surrogates exhibit unusual survival properties compared with other respiratory viruses, with survival times often measured in days, weeks or even months. Recent data suggests that MERS-CoV shares this property, surviving for >2 days when dried onto hard surfaces compared with only a few hours for influenza tested in the same study. Fortunately, these enveloped viruses are inactivated rapidly by usual hospital disinfectants, so I can understand the CDC’s recommendation for standard environmental disinfection.
So, how to protect yourself and your patients? The answer is simple for direct patient care: wear your gown, gloves, goggles and N95 (FFP3) mask, and wash your hands! It’s simple in theory, compliance with these measures in practice is not as good as you may expect. Prof Seto published a study in the Lancet in 2003 about compliance with personal protective equipment (PPE) and hand hygiene during the SARS epidemic. Remarkably, even when caring for patients known to be infected with SARS, <30% of healthcare workers self-reported that they wore a mask, glove, gown and washed their hands as they should have done. And this was self-reported, so you’d expect there to be a bias towards compliance! Most importantly, none of the healthcare workers who complied with all four measures became infected.
Figure: Healthcare worker compliance with mask, glove, gown use, and hand washing during the SARS epidemic, stratified by those who became infected with SARS.
To summarise: how to protect you and your patients from MERS-CoV:
- Place patient in negative pressure airborne infection isolation room, where available.
- Wear the correct PPE when in the room (gloves, gown, N95 / FFP3 mask, goggles), and wash your hands.
- Pay attention to the potential for contaminated surfaces and air, particularly following the discharge of the patient.
- Oh, and if you go on holiday to Saudi Arabia, don’t kiss any camels!
Reflections on Infection Prevention and Control 