26 June 2020
A number of studies highlight the importance of layering different public health measures, due to their cumulative effect on transmission reduction. Physical distancing, combined with other interventions such as international border closures, encouragement of individual measures (including cough etiquette and hand hygiene practices) and effective contact tracing, isolation and quarantine measures; have contributed to the suppression and control of COVID-19 in Australia, and in countries around the world.
The objective of physical distancing is to limit the spread of COVID-19, specifically by preventing person-to-person transmission. Physical distancing measures can be distinguished into two types of distancing: measures that reduce mixing between people and the rate of non-household contacts, referred to as ‘macro-distancing’ in pandemic modelling (e.g. restriction of gathering sizes, closure of bars/restaurants/cafes); and measures that create distance between individuals and reduce transmission probability per non-household contact, referred to as ‘micro-distancing’ in pandemic modelling (e.g. maintaining 1.5m distance between individuals). From other respiratory viruses, it is known that droplet transmission requires a certain proximity of people. A study that examined the distribution of influenza virus demonstrated an increased risk of transmission if within 1.8m of an infected individual. This evidence, combined with emerging evidence from China where COVID-19 was first detected, indicates droplets to be a major route of COVID-19 transmission. As such, in addition to a suite of other measures, the Australian Government swiftly made the recommendation for individuals to maintain a distance of 1.5m from others.
Evidence of the relative importance of maintaining appropriate distance between individuals has since emerged which confirms the need to continue this practice throughout the course of the pandemic. This is particularly important as we continue to adjust measures. A recent systematic review published in The Lancet examined the optimum distance to avoid personto-person transmission of COVID-19. They concluded that physical distancing of at least one metre was associated with a much lower risk of infection, and that based on modelling, a distance of two metres likely confers even greater protection. AHPPC therefore continues to recommend physical distancing of 1.5m between individuals.
Person Density Restrictions
It is acknowledged that there is a suite of principles that can be applied to limit COVID-19 transmission in venues, which include:
- Enabling 1.5m physical distancing between individuals who are not known to each other.
- Limiting the rate of interactions between individuals who are not known to each other, which includes:
- limiting the size of groups or maximum total number of persons in a venue
- limiting the mixing of individual groups.
- Considering activity-specific risk and applying specific mitigations.
- Hygiene measures, such as:
- hand hygiene, cough etiquette, and respiratory hygiene
- frequent environmental cleaning and disinfection to limit fomite transmission.
A number of measures can be applied to enable these principles, but for implementation purposes such measures must facilitate planning, be practical to implement, and simple to enforce. Whilst physical distancing is an individual responsibility, a density restriction is a measure that can be used in planning for gatherings.
A density restriction of one person per 4m2 contributes to limiting disease spread by:
- Enabling physical distancing of 1.5m between individuals, while accounting for objects that might occupy the floor space and reduce the available space for individuals to occupy, and for mobility of the people within the space.
- Limiting the size of groups and restricting the total number of persons in a premises, which limits individual interactions and mixing between groups.
- Limiting fomite transmission, by reducing the total number of people in a space contributing to the contamination of surfaces.
The density restriction is simple to use for planning purposes, and enforcement, as the total floor space of a premises is known. This simple measure can reduce the burden on contact tracing should a case occur, and reduce the probability that an outbreak might become unmanageable.
Risk Management in Small Premises
The one person per 4m2 density restriction (4m2 density rule) has proved to be an effective control measure. It is acknowledged, however, that blanket density restrictions disproportionately affect smaller businesses and premises, and must be balanced with the viability of re-opening businesses and stimulating the economy. AHPPC considers that a higher density of people in small groups presents a manageable risk in the context of low or no community transmission, as the relatively small numbers present are unlikely to place an excessive burden on contact tracing should an infectious individual attend the premises.
Under the ‘3-Step Framework’ jurisdictions have the flexibility to adjust measures to best suit local epidemiology and circumstances, and with other risk mitigations in place the 4m2 density rule may be adjusted in Step 3 to mitigate against the difficulties faced by smaller premises.
Where jurisdictions make adjustments to the 4m2 density rule for small premises, the following principles apply:
- Rules for small premises are not applicable to larger venues where smaller areas are created with walls/partitions/barriers/screens/ropes etc.
- Groups of individuals known to each other may be seated together but must be separated from other individuals or groups by a distance of 1.5m.
- People must be seated, as a higher density of people than one per 4m2 does not account for mobility within an area. Posture should be considered to avoid face-to-face posture between individuals and/or groups who are not known to each other.
- Businesses must prepare a COVID-19 plan for each premises in accordance with NCCC guidance and the Safe Work Australia National COVID-19 Safe Workplace Principles, to enable their business to open in a COVID Safe manner. This acknowledges that different activities are undertaken within premises, and that these activities will each have their own risk profiles for COVID-19 transmission.
Jurisdictions may choose to adjust the 4m2 rule for small premises by either:
- Allowing businesses to choose one of two options:
- Limit the number of patrons to 20 (excludes staff)
- If more than 20 patrons are desired, the 4m2 density rule applies
- A premises has a total floor area of 60m2, so the 4m2 rule would limit them to 15 patrons. They may, however, choose to admit up to 20 patrons if 1.5m physical distancing can be maintained between individuals or groups who are not known to each other.
- A premises wishes to seat 25 patrons for a function, hence they are required to apply the 4m2 rule. The total floor area of the premises must be at least 100m2 to accommodate 25 patrons, and must allow for 1.5m physical distancing between individuals or groups who are not known to each other.
- Allowing a higher person-density, such as one person per 2m2. Jurisdictions will determine the definition of a small premises for this option (e.g. a total floor area of <= 100m2).