The only randomized, controlled study of cloth masks warns against their use, as they INCREASE the risk of COVID-19 infection by 13%

[Mark Crispin Miller]

A cluster randomised trial of cloth masks compared with medical masks in healthcare workers 

C Raina MacIntyre,1 Holly Seale,1 Tham Chi Dung,2 Nguyen Tran Hien,2 Phan Thi Nga,2 Abrar Ahmad Chughtai,1 Bayzidur Rahman,1 Dominic E Dwyer,3 Quanyi Wang4 To cite: MacIntyre CR, Seale H, Dung TC, et al. 

https://bmjopen.bmj.com/content/bmjopen/5/4/e006577.full.pdf

A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ Open 2015;5: e006577. doi:10.1136/ bmjopen-2014-006577 ▸ 

Prepublication history for this paper is available online. To view these files please visit the journal online (http://dx.doi.org/10.1136/ bmjopen-2014-006577). 

Received 9 September 2014 Revised 25 March 2015 Accepted 26 March 2015 For numbered affiliations see end of article. Correspondence to Professor C Raina 

MacIntyre; r.mac...@unsw.edu.au 

ABSTRACT 

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 laboratoryconfirmed 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 laboratoryconfirmed 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 Z