Routes of Transmission
Based on current understanding, three main routes of viral transmission are relevant for SARS-CoV-2, the virus that causes COVID-19. COVID-19 outbreak investigations and infectious disease models indicate that all three routes of transmission are important, and the relative importance of the different routes of transmission can vary depending on scenario-specific details.
When we breathe normally, speak, sing, and cough or sneeze, we release aerosols of all different size ranges. These aerosols produced in the respiratory system can carry the SARS-CoV-2 virus if someone is infected. Some of these aerosols, or particles, are large (in a physics sense) and do not travel far (see Droplet Transmission). These droplets will fall out of the air within six feet. However, most of the aerosols that carry the virus are small enough that they can float in the air for longer periods of time, travel beyond six feet, and can concentrate in a room that does not have good ventilation and/or filtration. Airborne transmission can occur if someone breathes these aerosols that contain the virus. Importantly, being closer to someone who is infectious and releasing virus increases the intensity, or amount, of the airborne virus that is inhaled. Airborne transmission risk can be reduced by mask wearing, increasing distance between people, and by implementing changes to the building, such as increasing the amount of outdoor air ventilation and/or opening windows to bring extra outdoor air into an indoor space, and increasing the degree to which air is filtered in the building mechanical system.
Droplet transmission is a type of direct transmission that refers to close-range transmission of virus by sometimes-visible droplets that are coughed or sneezed by an infectious person. These “respiratory droplets,” as they are called, are large enough that they travel only a short distance before settling out of the air onto surrounding surfaces. If, however, droplets produced by a person who is shedding virus get into the eyes, mouth, or nose of a person in their immediate vicinity, this second person may get infected. In a theater scenario, this type of “close contact” droplet transmission could occur, for example, when audience members are crowded together in a busy lobby or when performers interact intimately onstage. Droplet transmission of a virus can be minimized by physical distancing (e.g. de-densifying indoor spaces so individuals do not come into close proximity with each other), wearing masks, and covering coughs and sneezes.
Fomites are any inanimate objects that can act as a source of transference for a virus. The term “fomite” (or “fomes”) goes as far back as the 1500s, when it was recognized that surfaces could be “seeds of disease.” This type of indirect transmission happens when a surface is contaminated with virus after an infectious person coughs directly onto the surface or after they sneeze into their hand and then touch the surface. The fomite could be a source of viral illness for anyone who touches it while the virus remains present and then transfers that virus into their body through their mouth or nose. In a theater context, fomites could include shared props, bathroom faucets, or door handles. Fomite transmission of a virus can be minimized through frequent cleaning and disinfection of commonly-touched objects, through use of automatic or touchless alternatives (e.g. automatic doors), and through hand-washing immediately after touching a shared object. While fomite transmission can happen, the latest science indicates it is rare, and it is best addressed through good hand hygiene.
Hierarchy of Controls
The Hierarchy of Controls is a “layered defense” framework used in the field of worker health and safety that helps clarify what kinds of interventions should be considered and prioritized when trying to address a workplace hazard.
The levels of the Hierarchy, explained in detail below, are ordered from most effective (elimination) to least effective (PPE), and interventions on multiple levels can and should be combined. When using the Hierarchy as a framework to develop protections against a specific hazard like COVID-19, it is helpful to start at the first level (elimination) and consider what aspects of theater can be addressed at this level (i.e. what activities can be done remotely). If elimination of the hazard is not possible, proceed to each subsequent level to determine whether, and how, that control can be used to address the hazard. This process helps to make sure that the most effective interventions are implemented first and that additional protections are pursued when more effective interventions are not possible.
The levels of the Hierarchy of Controls, along with examples of how they could be used to address COVID-19 in a theater context, are listed below.
Hazard elimination refers to altering a task or process to entirely remove the threat of a potential hazard. This is the most effective way to address a hazard. In a theater context, hazard elimination involves identifying which activities could be conducted remotely, in order to directly eliminate the possibility of virus transmission in the workplace. For example, theaters might consider having administrative staff continue to work from home and moving segments of the rehearsal process online.
Substitution refers to replacing a hazard with a non-hazardous alternative when elimination is not feasible. In a theater context, this might involve asking what in-person work routines might be replaced with safer alternatives. For example, outdoor rehearsals could be substituted for indoor ones, always following additional administrative controls (e.g. distancing requirements) and PPE guidelines. This control strategy also involves identifying the minimum number of core people that need to be physically present in the building for any activity.
Engineering controls refer to technologies or barriers that are installed to prevent people from encountering a hazard. These can be broadly thought of as “Healthy Building” strategies. Theater companies might ask what changes to their facilities could be made in order to minimize risk. For example, management could consider enhanced ventilation and filtration, the use of portable air cleaners in smaller rooms, enhanced cleaning and disinfection protocols, plexiglass shielding in some locations, and no-touch bathrooms.
Administrative controls are protocols, procedures, or rules that are put in place to reduce risk. In the context of theaters managing their response to COVID-19, this control strategy involves policies and procedures which can be used to minimize shared surfaces and maintain sufficient physical distancing. For example, everyone at in-person rehearsals adheres to policies for proximity and physical contact, as well as rules requiring frequent hand washing. Administrative controls at theaters could also include strategies for screening and de-densifying audiences, including measures taken to choreograph crowd flow into and out of performance spaces.
PPE stands for personal protective equipment and includes items such as gloves or masks worn by people exposed to various hazards. The goal is always to try to reduce the risk of the hazard through the other levels of control before having to resort to PPE. However, this is not always possible, as is the case with SARS-CoV-2. Therefore, universal masking is essential as a control strategy. Importantly, not all masks are created equal. Some cloth masks may provide only 50% capture efficiency for respiratory aerosols, while a common three-layer mask (e.g., blue surgical mask) can provide 70% efficiency. A three-layer mask is the minimum recommended level of protection. When everyone is wearing this type of mask, the combined benefit is 91% exposure reduction, because respiratory aerosols have to pass through two masks. For higher-risk activities, consider masks with higher filtration efficiencies, such as a certified N95 made in the U.S. or certified KF94 made in South Korea.