Keywords: Key words and database search strings: Related to masks: masks, respirators, face coverings, non-pharmaceutical interventions (NPIs), respiratory protective devices. Related to respiratory outbreaks: respiratory outbreak, respiratory pandemic, epidemic control, public health intervention, Specific respiratory illness keywords: COVID-19, SARS-CoV-2, influenza, SARS (Severe Acute Respiratory Syndrome), MERS (Middle East Respiratory Syndrome). Outcome and Effect Keywords: transmission rate, infection rate, disease spread, hospitalization rate, mortality rate, community transmission, effectiveness, impact, efficacy. Mechanism keywords: aerosols, air filtration, filtration efficiency, adsorption, absorption, breathability, fit factor, mask efficiency, mask coatings, antibacterial Database Search Strategies: Combine keywords using Boolean operators (AND, OR, NOT). Example: (mask*) AND (COVID-19 OR influenza) AND transmission rate Use truncation (*) to capture variations of words. Example: mask* will find masks, masking, etc. Use phrase searching (quotation marks) to find exact phrases. Example: public health intervention Use MeSH terms (Medical Subject Headings) in PubMed/MEDLINE for more precise results. Example Search Strings: PubMed: (mask*[Title/Abstract] OR face covering[Title/Abstract]) AND (COVID-19[MeSH Terms] OR influenza[MeSH Terms]) AND (transmission[Title/Abstract] OR infection[Title/Abstract]) Google Scholar: mask* AND (respiratory outbreak OR pandemic) AND (transmission OR effectiveness) These keywords and search strategies will be piloted in the specific databases and modified in response to emerging findings.