A cluster randomised trial of cloth masks compared with medical masks in healthcare workers
C Raina MacIntyre, Holly Seale, Tham Chi Dung, Nguyen Tran Hien, Phan Thi Nga, Abrar Ahmad Chughtai, Bayzidur Rahman, Dominic E Dwyer, Quanyi Wang
The authors of this article, published in 2015, have written a response to their work in light of the COVID-19 pandemic. We urge our readers to consider the response when reading the article. https://bmjopen.bmj.com/content/5/4/e006577.responses#covid-19-shortages-of-masks-and-the-use-of-cloth-masks-as-a-last-resort
Objective The aim of this study was to compare the efficacy of cloth masks to medical masks in hospital healthcare workers (HCWs).
The null hypothesis is that there is no difference between medical masks and cloth masks.
Setting 14 secondary-level/tertiary-level hospitals in Hanoi, Vietnam.
Participants 1607 hospital HCWs aged ≥18 years working full-time in selected high-risk wards.
Intervention Hospital wards were randomised to: medical masks, cloth masks or a control group (usual practice, which included mask wearing).
Participants used the mask on every shift for 4 consecutive weeks.
Main outcome measure Clinical respiratory illness (CRI), influenza-like illness (ILI) and laboratory-confirmed respiratory virus infection.
Results The rates of all infection outcomes were highest in the cloth mask arm, with the rate of ILI statistically significantly higher in the cloth mask arm (relative risk (RR)=13.00, 95% CI 1.69 to 100.07) compared with the medical mask arm.
Cloth masks also had significantly higher rates of ILI compared with the control arm.
An analysis by mask use showed ILI (RR=6.64, 95% CI 1.45 to 28.65) and laboratory-confirmed virus (RR=1.72, 95% CI 1.01 to 2.94) were significantly higher in the cloth masks group compared with the medical masks group.
Penetration of cloth masks by particles was almost 97% and medical masks 44%.
Conclusions This study is the first RCT of cloth masks, and the results caution against the use of cloth masks. This is an important finding to inform occupational health and safety. Moisture retention, reuse of cloth masks and poor filtration may result in increased risk of infection. Further research is needed to inform the widespread use of cloth masks globally. However, as a precautionary measure, cloth masks should not be recommended for HCWs, particularly in high-risk situations, and guidelines need to be updated.
Trial registration number Australian New Zealand Clinical Trials Registry: ACTRN12610000887077.
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Strengths and limitations of this study
The use of cloth masks is widespread around the world, particularly in countries at high-risk for emerging infections, but there have been no efficacy studies to underpin their use.
This study is large, a prospective randomised clinical trial (RCT) and the first RCT ever conducted of cloth masks.
The use of cloth masks are not addressed in most guidelines for health care workers—this study provides data to update guidelines.
The control arm was ‘standard practice’, which comprised mask use in a high proportion of participants. As such (without a no-mask control), the finding of a much higher rate of infection in the cloth mask arm could be interpreted as harm caused by cloth masks, efficacy of medical masks, or most likely a combination of both.
The use of facemasks and respirators for the protection of healthcare workers (HCWs) has received renewed interest following the 2009 influenza pandemic,1 and emerging infectious diseases such as avian influenza,2Middle East respiratory syndrome coronavirus (MERS-coronavirus)3 ,4 and Ebola virus.5 Historically, various types of cloth/cotton masks (referred to here after as ‘cloth masks’) have been used to protect HCWs.6 Disposable medical/surgical masks (referred to here after as ‘medical masks’) were introduced into healthcare in the mid 19th century, followed later by respirators.7 Compared with other parts of the world, the use of face masks is more prevalent in Asian countries, such as China and Vietnam.8–11
In high resource settings, disposable medical masks and respirators have long since replaced the use of cloth masks in hospitals. Yet cloth masks remain widely used globally, including in Asian countries, which have historically been affected by emerging infectious diseases, as well as in West Africa, in the context of shortages of personal protective equipment (PPE).12 ,13 It has been shown that medical research disproportionately favours diseases of wealthy countries, and there is a lack of research on the health needs of poorer countries.14 Further, there is a lack of high-quality studies around the use of facemasks and respirators in the healthcare setting, with only four randomised clinical trials (RCTs) to date.15 Despite widespread use, cloth masks are rarely mentioned in policy documents,16 and have never been tested for efficacy in a RCT. Very few studies have been conducted around the clinical effectiveness of cloth masks, and most available studies are observational or in vitro.6 Emerging infectious diseases are not constrained within geographical borders, so it is important for global disease control that use of cloth masks be underpinned by evidence. The aim of this study was to determine the efficacy of cloth masks compared with medical masks in HCWs working in high-risk hospital wards, against the prevention of respiratory infections.
A cluster-randomised trial of medical and cloth mask use for HCWs was conducted in 14 hospitals in Hanoi, Vietnam. The trial started on the 3 March 2011, with rolling recruitment undertaken between 3 March 2011 and 10 March 2011. Participants were followed during the same calendar time for 4 weeks of facemasks use and then one additional week for appearance of symptoms. An invitation letter was sent to 32 hospitals in Hanoi, of which 16 agreed to participate. One hospital did not meet the eligibility criteria; therefore, 74 wards in 15 hospitals were randomised. Following the randomisation process, one hospital withdrew from the study because of a nosocomial outbreak of rubella.
Participants provided written informed consent prior to initiation of the trial.
Seventy-four wards (emergency, infectious/respiratory disease, intensive care and paediatrics) were selected as high-risk settings for occupational exposure to respiratory infections. Cluster randomisation was used because the outcome of interest was respiratory infectious diseases, where prevention of one infection in an individual can prevent a chain of subsequent transmission in closed settings.8 ,9 Epi info V.6 was used to generate a randomisation allocation and 74 wards were randomly allocated to the interventions.
From the eligible wards 1868 HCWs were approached to participate. After providing informed consent, 1607 participants were randomised by ward to three arms: (1) medical masks at all times on their work shift; (2) cloth masks at all times on shift or (3) control arm (standard practice, which may or may not include mask use). Standard practice was used as control because the IRB deemed it unethical to ask participants to not wear a mask. We studied continuous mask use (defined as wearing masks all the time during a work shift, except while in the toilet or during tea or lunch breaks) because this reflects current practice in high-risk settings in Asia.8
The laboratory results were blinded and laboratory testing was conducted in a blinded fashion. As facemask use is a visible intervention, clinical end points could not be blinded. Figure 1 outlines the recruitment and randomisation process.