








key: cord-316266-6m9g3bdr
authors: Jones, Peter; Roberts, Sally; Hotu, Cheri; Kamona, Sinan
title: What proportion of healthcare worker masks carry virus? A systematic review
date: 2020-06-24
journal: Emerg Med Australas
DOI: 10.1111/1742-6723.13581
sha: 
doc_id: 316266
cord_uid: 6m9g3bdr

BACKGROUND: Concerns have been raised by healthcare organisations in New Zealand that routine mask use by healthcare workers (HCW) may increase the risk of transmission of SARS‐CoV‐2 through increased face touching. Routine mask use by frontline HCW was not recommended when seeing ‘low risk’ patients. The aim of this review was to determine the carriage of respiratory viruses on facemasks used by HCW. METHODS: A systematic review was conducted with structured searches of medical and allied health databases. Two authors independently screened articles for inclusion, with substantial agreement (k=0.66, 95%CI 0.54 to 0.79). Studies that at least one author recommended for full text review were reviewed in full for inclusion. Two authors independently extracted data from included studies including the setting, method of analysis and results. There was exact agreement on the proportion of virus detected on masks. RESULTS: 1233 titles were retrieved, 47 underwent full text review and five studies reported in four articles were included. The studies were limited by small numbers and failure to test all eligible masks in some studies. The proportion in each study ranged from 0 (95% CI 0‐10) to 25% (95%CI 8‐54). No study reported clinical respiratory illness as a result of virus on the masks. CONCLUSIONS: Although limited, current evidence suggests that viral carriage on the outer surface of surgical masks worn by HCW treating patients with clinical respiratory illness is low and there was not strong evidence to support the assumption that mask use may increase the risk of viral transmission. This article is protected by copyright. All rights reserved.

During the current novel coronavirus disease 2019 (SARS-CoV-2, COVID-19) pandemic, the Ministry of Health (MOH) and District Health Boards (DHB) have not recommended routine use of surgical masks for healthcare workers (HCW) in emergency departments (ED) in New Zealand (NZ). Such advice was contrary to the experience of countries that had faced similar pandemics previously who recommended use of masks for ED staff within days of the first cases presenting. 1 2 The initial drivers for this were a belief that the risk to HCW from patients without epidemiological (travel/known contact) risk factors and clinical respiratory illness (CRI) and fever was very low and that overuse of masks could jeopardise the available supply later in the pandemic when the prevalence of CRI in the population presenting to ED would be higher. This advice was consistent with the contemporaneous World Health Organisation (WHO) guidelines on rational use of personal protective equipment (PPE) for coronavirus disease 2019, based on droplets being the most likely mode of virus transmission. 3 However, emerging evidence from the current SARS CoV-2 pandemic suggests that aerosol and asymptomatic spread are both possible. [4] [5] [6] The case definition in NZ subsequently changed to include any respiratory illness regardless of fever or epidemiological risk. Evidence has also emerged that as many of 50% of infected people are asymptomatic. 6 7 This prompted a change in advice such that currently mask use is permitted, with warnings that incorrect use of masks may be harmful, including concerns that mask use may "actually increase your risk of COVID-19". 8 The aim of this review was to determine the carriage of respiratory viruses on facemasks used by HCW in acute care settings, to inform a recommendation on mask usage in the ED in the setting of an emerging viral pandemic. The primary outcome is the proportion of masks positive for any respiratory viruses. The secondary aim was to determine whether viral carriage on masks used by HCW increased or decreased the risk of CRI for staff.

Structured searches were conducted in Medline, Embase and CInAHL using free text and MeSH terms for 'mask'; 'touch'; 'nosocomial infection'; 'contamination' and 'virus' (supplementary file).

The final search was run on 23/4/20. These were supplemented by a citation search of included articles. There was no restriction on year or language.

Two authors independently screened titles and abstracts for relevance and selected articles for full text review. Articles were included if they were clinical studies that reported virus detection on masks worn by HCW. Experimental studies and computer simulation studies were excluded, as were letters to the editor or opinion pieces. Agreement between authors on study selection was substantial, 10 with 97.6% exact agreement (k=0.66, 95%CI 0.54 to 0.79). All studies that at least one author recommended for full text review were reviewed in full for inclusion. Two authors independently extracted data from included studies into a table including the setting, type of study, method of analysis and results. There was exact agreement on the proportion of virus detected on masks from the included studies.

Accepted Article 6 Data from included studies was shown using descriptive statistics: n, proportion, 95% confidence interval (calculated using Graphpad https://www.graphpad.com/quickcalcs/confInterval1/), San Diego CA, USA.

When it was unclear whether studies reported virus detection on multiple sites on the same mask, we reported the highest and lowest possible proportions.

Risk of bias was assessed in the studies based on mask selection, method of sampling and detection, and reporting and rated as high, low or unclear.

As a secondary analysis of published aggregate data, ethical approval was not required. This review was not registered in a review registry.

Patients and the public were not involved in this study.

The searches retrieved 1233 titles and abstracts, 1186 were either irrelevant or duplicates and 47 underwent full text review (figure 1). Forty studies did not report viral presence on masks and three were simulation or theoretical modelling studies 11-13 so were excluded. Five studies reported in four articles met the inclusion criteria and were included. [14] [15] [16] [17] The settings, methods, proportion positive and types of viruses are presented in Table 1 . The risk of bias for each study is also shown in this table.

The proportion in each study ranged from 0 (95% CI 0-10) to 25% (95% CI 8-54). For the largest study with 148 participants, the proportion was 10.1% (95% CI 6-16), shown in Figure 2 . None of the included studies reported whether any staff subsequently developed CRI related to detectable virus on their masks.

This is the first systematic review of viral detection on masks worn by HCW to our knowledge.

No studies were conducted in the ED setting in the context of an emerging viral pandemic, which means the evidence relating to ED is indirect.

The available evidence suggests that between 0 and 25% of masks worn by staff seeing patients with symptomatic viral illness had a detectable virus and few had virus detected on their faces after doffing masks. Where reported, the viral loads on masks were small, and infectivity was not reported. Without a control group not wearing masks (which may be considered unethical) it is not possible to say whether this was better or worse than not wearing a mask.

The studies ranged in quality, with the main methodological concern being lack of testing of all eligible masks in several studies. There was a tendency for more testing in higher risk settings and masks that were more likely to be contaminated, which would bias towards finding a higher proportion of viral carriage on the tested masks. Whilst all five studies used molecular methods to detect viral particles, the method of sampling differed with two studies reported in one article removing the outer layer of the mask, 15 two punching full-thickness 25 mm coupons from the mask 14 17 and one swabbing the surface of the outer layer. 16 Three studies reported the level of detection (LOD) for the polymerase chain reaction (PCR) assay. 14 16 17 This limits the comparison between studies.

With respect to whether wearing masks increases facial touching by HCW, one study found that HCW wearing masks touched their faces during 29% and heads in 8% of care episodes for patients with CRI. The median number of mask contacts ranged from one per hour in the near patient zone and five per hour in the far patient zone. 18 In this study, there was no control group to see how often staff touched their faces or heads when not wearing masks. In comparison, a study of medical students in a lecture found the rate of face touching to be 23 times per hour per student (without Accepted Article 9 masks). 19 Another study found that gloves (31%) and gowns (21%) of HCW had more detectable virus than masks after single use caring for a patient with CRI (12%). 16 Wearing masks for more than six hours continuously and seeing more than 25 patients per shift were associated with a higher chance of mask contamination in one study. 15 None of the included studies reported CRI in the staff studied, so it is not possible to say whether detecting virus on the mask leads to a higher risk of contracting CRI.

Systematic review evidence from a previous coronavirus pandemic suggests that general use of masks may be protective for HCW in this setting, 20 21 with a Number Needed to Treat (NNT) of six to prevent one HCW infection (meta-analysis of case control studies). 22 In contrast, there is one case report of a HCW who contracted Middle Eastern Respiratory Syndrome-related coronavirus (MERS-CoV) after performing CPR for one hour in full PPE on a patient with cardiac arrest due to MERS-CoV pneumonia with gross haemoptysis. 23 During the resuscitation the staff member was seen to adjust their mask and goggles with a heavily soiled glove. General use of masks by staff early in the course of the current 1 and previous 2 The current WHO advice on use of surgical masks emphasises that these should be prioritised for HCW rather than for general public use in the community. The advice for HCW is to wear a surgical mask when entering rooms "where patients with suspected or confirmed COVID-19 are admitted" but does not address the use of surgical masks by HCW in ED who are seeing other patients. 25 26 Given the low proportion of virus detection on masks and lack of evidence that this is linked to CRI, it may be prudent for HCW in the ED to wear masks routinely in clinical areas as part of a comprehensive bundle of measures to prevent nosocomial infection. This is especially so when

This article is protected by copyright. All rights reserved. 

Although limited, current evidence suggests that viral carriage on the outer surface of surgical masks worn by HCW treating patients with CRI is between 0 and 25%.

No funding was sought or received for this study. The author has no financial or other relationships of interest with any manufacturer of medical masks.

Accepted Article

Accepted Article 

This article is protected by copyright. All rights reserved.

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Accepted Article This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved. Accepted ArticleThis article is protected by copyright. All rights reserved.

