Use of antimicrobial mouthwashes (gargling) and nasal sprays by healthcare workers to protect them when treating patients with suspected or confirmed COVID‐19 infection

Background
COVID‐19 infection poses a serious risk to patients and – due to its contagious nature – to those healthcare workers (HCWs) treating them. If the mouth and nose of HCWs are irrigated with antimicrobial solutions, this may help reduce the risk of active infection being passed from infected patients to HCWs through droplet transmission or direct contact. However, the use of such antimicrobial solutions may be associated with harms related to the toxicity of the solutions themselves, or alterations in the natural microbial flora of the mouth or nose. Understanding these possible side effects is particularly important when the HCWs are otherwise fit and well.

Objectives
To assess the benefits and harms of antimicrobial mouthwashes and nasal sprays used by healthcare workers (HCWs) to protect themselves when treating patients with suspected or confirmed COVID‐19 infection.

Search methods
Information Specialists from Cochrane ENT and Cochrane Oral Health searched the Central Register of Controlled Trials (CENTRAL 2020, Issue 6); Ovid MEDLINE; Ovid Embase and additional sources for published and unpublished trials. The date of the search was 1 June 2020.

Selection criteria
This is a question that urgently requires evidence, however at the present time we did not anticipate finding many completed randomised controlled trials (RCTs). We therefore planned to include the following types of studies: RCTs; quasi‐RCTs; non‐randomised controlled trials; prospective cohort studies; retrospective cohort studies; cross‐sectional studies; controlled before‐and‐after studies. We set no minimum duration for the studies.

We sought studies comparing any antimicrobial mouthwash and/or nasal spray (alone or in combination) at any concentration, delivered to HCWs, with or without the same intervention being given to the patients with COVID‐19.

Data collection and analysis
We used standard Cochrane methodological procedures. Our primary outcomes were: 1) incidence of symptomatic or test‐positive COVID‐19 infection in HCWs; 2) significant adverse event: anosmia (or disturbance in sense of smell). Our secondary outcomes were: 3) viral content of aerosol, when present (if intervention administered to patients); 4) other adverse events: changes in microbiome in oral cavity, nasal cavity, oro‐ or nasopharynx; 5) other adverse events: allergy, irritation/burning of nasal, oral or oropharyngeal mucosa (e.g. erosions, ulcers, bleeding), long‐term staining of mucous membranes or teeth, accidental ingestion. We planned to use GRADE to assess the certainty of the evidence for each outcome.

Main results
We found no completed studies to include in this review. We identified three ongoing studies (including two RCTs), which aim to enrol nearly 700 participants. The interventions included in these trials are povidone iodine, nitric oxide and GLS‐1200 oral spray (the constituent of this spray is unclear and may not be antimicrobial in nature).

Authors' conclusions
We identified no studies for inclusion in this review. This is not surprising given the relatively recent emergence of COVID‐19 infection. It is promising that the question posed in this review is being addressed by two RCTs and a non‐randomised study. We are concerned that only one of the ongoing studies specifically states that it will evaluate adverse events and it is not clear if this will include changes in the sense of smell or to the oral and nasal microbiota, and any consequences thereof.

Very few interventions have large and dramatic effect sizes. If a positive treatment effect is demonstrated when studies are available for inclusion in this review, it may not be large. In these circumstances in particular, where those receiving the intervention are otherwise fit and well, it may be a challenge to weigh up the benefits against the harms if the latter are of uncertain frequency and severity.