One of the key issues for healthcare systems around the world during the covid-19 pandemic has been the lack of sufficient personal protective equipment (PPE) available for healthcare workers. We recently updated a Cochrane review on PPE for healthcare workers.  The review included 22 simulation studies and two field studies comparing types of PPE used within a full-body PPE ensemble. The review found evidence that covering more parts of the body, such as the neck and the head, may lead to better protection, but at the cost of being more difficult to put on or take off. Studies showed that modifications to the design of PPE, including tabs to grab or better coverage of the glove-gown interface may lead to less contamination.  Better guidance on doffing, one-step glove and gown removal, double-gloving, verbal instructions during doffing, and using glove disinfection may all reduce contamination and increase compliance. We found only three studies that evaluated improving instruction and training for PPE use; none looked at maintaining skills in the long run.  All evidence was rated as low to very low quality. We downgraded simulation studies because they were indirectly related to the PPE issues and most comparisons were based on single studies. So, what can we learn from the Cochrane review in light of the current covid-19 pandemic?
Recently, debate and controversy have surrounded the types of masks or respirators that should be used by healthcare workers. A key point, often overlooked, is that it is not just masks or respirators that help protect their users from infection. It is the totality of the PPE elements used in combination, including gloves, gowns, masks, and face shields that offer protection within a larger hierarchy of control measures. 
Healthcare workers are at much greater risk of acquiring serious infections than the general population. This fact has been demonstrated during epidemics such as SARS, Ebola, and covid-19. In general, the risk of acquiring infection depends on the chance of encountering an infected person and on the time being exposed to this person. Compared to non-healthcare workers, many healthcare workers have a much greater risk because they are routinely exposed to contaminated body fluids such as secretions, excretions, and aerosolised droplets from patients who are infected with highly contagious diseases for prolonged periods. 
Measures to help prevent healthcare workers from becoming infected at work should be considered from the perspectives of occupational health and infection control point of view. From the occupational health perspective, it is a matter of reducing and preventing exposure to contaminated body fluids and other potentially infectious materials and contaminated surfaces. It is good practice to use a hierarchy of controls. This means that there should be a fixed order in which to consider measures to control exposure. First, one should consider measures that eliminate exposure. For example, reorganising patient flows in a hospital will greatly reduce exposure of those healthcare workers not directly involved in clinical work to patients with confirmed infectious diseases. Next, technical measures to reduce exposure should be considered, such as, when possible, choosing local or regional anaesthesia to avoid aerosol generating intubation or ensuring adequate ventilation and cleaning. Exposure can be further reduced by establishing sustainable infection prevention and control measures. PPE should be considered as the last line of defence since PPE generally reduces healthcare workers’ comfort, restricts their movement, and necessitates time and a designated place to put it on and take it off.  In addition, the protection provided by PPE depends on human factors including proper selection and use of the PPE and correctly donning and doffing it. Nevertheless, it is hard to imagine a situation in general in which healthcare workers could do without PPE. Therefore, it is important to find out if PPE works and which types work best.
The theory behind PPE is simple. One should block the main routes of pathogen entry by covering the mouth, nose, eyes, and exposed body parts with sufficiently protective materials. It must be possible to take the materials off without the risk of self-contamination. Gowns cover more of the exposed body parts than aprons while they are both easy to remove safely.  However, balancing the goal of providing adequate coverage and safety while donning and doffing can also be difficult. For example, as highlighted in our Cochrane review, gowns are relatively easier to put on and, in particular, to take off compared to coveralls. Gowns are generally more familiar to healthcare workers and hence more likely to be used and removed correctly, but gowns do not provide continuous whole-body protection because of openings in the back and coverage to the mid-calf only.  Coveralls, on the other hand, typically provide 360-degree protection because they are designed to cover the whole body. The level of heat stress is greater when using coveralls rather than gowns. Removing coveralls without self-contamination is probably more difficult. In addition, when aerosol transmission is likely there should also be proper respiratory protection to prevent inhalation of airborne virus particles. Observational studies during the SARS and Ebola epidemics have shown that putting on even one PPE-item such as gloves helped to reduce the risk of infection with additional items, such as gowns, masks, or goggles providing additional protection and greater reduction.  This still leaves us with the question which PPE ensemble, or combination of items, is most appropriate in each healthcare setting.
There should be a clear objective about what PPE should achieve. For example, to protect body parts from exposure to viral contamination, one must specify which body parts need covering, and what types of garment can be used to achieve this.
The next consideration is the technical quality standards of the PPE that need to be followed. Even though there has been progress in unifying technical quality standards, there is still variation. For example, EU and US standards for surgical gowns differ, and there is no specific EU standard for isolation gowns. [6,7] The interpretation of the standards is still difficult and requires expert knowledge.
PPE needs to be feasible in health care settings because protection depends not only on the technical qualities of the garment but also on the composition of PPE items, interfaces between pieces of PPE, and the ways in which they are put on and taken off. Simulation studies can measure the feasibility. 
Finally, and ideally, there should be evidence that the PPE reduces infection in “real-life” health care situations, because we do not know how well simulation studies can predict protection. Randomised trials are needed to increase the certainty of the evidence. A cluster randomized trial has been shown to be feasible for the evaluation of surgical masks versus filtering facepiece respirators.  However, we do realize that it is difficult to conduct such studies during the hectic and uncertain times of epidemics or a pandemic. A realistic alternative is to conduct observational studies in which the PPE of health care workers is registered prospectively, and the health care workers are followed for their risk of infection.
The covid-19 pandemic has once again made it clear how important PPE is for the safety of millions of healthcare workers across the world. It is very disappointing that the evidence base for the effectiveness of PPE is still so small. Nevertheless, we believe that current guidance about PPE use can be improved by considering the balance of increased coverage of exposed body parts such as neck and head against increased discomfort and safety of donning and doffing. Doffing procedures can also be improved by better designed PPE. There is a need for harmonisation of standard specifications and test methods. We especially call on PPE manufacturers to improve their products according to the needs of healthcare workers and the existing evidence, and to have them evaluated under real life-circumstances.
Jos Verbeek is an occupational health physician and the coordinating editor of the Cochrane Work review group. Together with the review team, he conducted the Cochrane Review and wrote this opinion piece.
Cochrane review group:
Jos H Verbeek, Cochrane Work Review Group, Academic Medical Center, University of Amsterdam, Amsterdam, Netherlands
Elaine Toomey, University of Limerick, Ireland.
Blair Rajamaki, School of Pharmacy, University of Eastern Finland, Kuopio, Finland.
F Selcen Kilinc Balci, National Personal Protective Technology Laboratory (NPPTL), National Institute for Occupational Safety and Health (NIOSH), Centers for Disease Control and Prevention (CDC), Pittsburgh, PA, USA
Jani H Ruotsalainen, Assessment of Pharmacotherapies, Finnish Medicines Agency, Kuopio, Finland.
Bronagh Blackwood, Centre for Experimental Medicine, School of Medicine, Dentistry and Biomedical Sciences, Queen’s University Belfast, Belfast, UK.
Riitta Sauni, University of Tampere, Tampere, Finland.
Christina Tikka, Finnish Institute of Occupational Health, TYÖTERVEYSLAITOS, Finland.
Sharea Ijaz, Population Health Sciences, NIHR ARC West, Bristol Medical School, University of Bristol, Bristol, UK.
Competing interests: None of the authors has competing interests to declare in relation to this topic
Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention or the NIHR ARC West.
- Verbeek JH, Rajamaki B, Ijaz S, et al. Personal protective equipment for preventing highly infectious diseases due to exposure to contaminated body fluids in healthcare staff. Cochrane Database Syst Rev 2020;4:CD011621. doi: 10.1002/14651858.CD011621.pub4
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- Houghton C, Meskell P, Delaney H, et al. Barriers and facilitators to healthcare workers’ adherence with infection prevention and control (IPC) guidelines for respiratory infectious diseases: a rapid qualitative evidence synthesis. Cochrane Database of Systematic Reviews 2020(4) doi: 10.1002/14651858.CD013582
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