Opinion: What’s the environment got to do with health?

Clive Broadbent, AM, L.AIRAH, is a world-renowned expert on microbial control and was involved in responding to the SARS outbreak in 2003. At that time he formed part of a WHO team that travelled to China to analyse the spread of the virus and produce guidelines on laboratory standards, hospital practices and appropriate ventilation for SARS patients. He shares his views on the concept of environmental health.

When thinking of health, we generally think of public health, i.e., the transmission of disease from one person to another. And for the past year, front pages of newspapers have hardly covered any topic other than that of COVID-19.

But such public health concerns are only part of overall health. For example, there’s occupational health, generally styled as occupational health and safety (OHS). There’s economic health. There’s social/cultural health. There could even be an example of health styled as the “political health” of a country.

In terms of actual human disease, though, there is a wider type that is called environmental health. This is concerned with the impacts of the environment on the human population. It was once recognised as the cornerstone of public health, and as such was responsible for most of the improvements in life expectancy and health and wellness on life’s journey.

Many of the fundamental lessons on health, however, were arguably lost as modern societies travelled an increasingly medical and clinical road during the years since, say, World War II. Behind such advances is the need for environmental health in sustaining population health. Changes to our lifestyle, increasing urbanisation, population growth, resource depletion, air and water pollution, and building designs have created challenges within the discipline of environmental health.

Environmental health

Environmental health was once the backbone for maintaining effective sewage systems and clean water supplies – aspects now taken for granted, although they were once hidden from view, as such. Now such aspects have been joined by the need to tackle the impacts of global warming, ozone layer depletion, habitat loss, species depletion, chemical pollution, environmental degradation and other unforeseen issues.

Environmental health is not quite the same as environmental protection, which is concerned with protecting the environment from people. But environmental health overlaps both public health and environmental protection.

Historically, much modern public health began in the UK at a time when the governments circa 1810 to 1870 had the view that governments shouldn’t interfere in such matters. But then came an epidemic of cholera in London and the work of John Snow in 1854. Snow removed the handle of a water pump in Broad Street London because the epidemiology pointed to that well water being the centre of a major outbreak.

Eventually the connection with sewage in the underground aquifer was recognised. This led to a Public Health Act in the UK on sanitary conditions for water supplies, which was quickly followed by the state of Victoria in the 1850s – the first jurisdiction outside the UK. 

Perhaps simplistically put, basic public health needs were then followed by a focus on personal protection such as vaccination, curative medicines, testing, treatment and latterly behaviour and lifestyle. Environmental protection laws too, after a series of pollution disasters worldwide, led to a transfer of functions from health departments to environmental protection agencies.

Community health plans now abound. These are all good, but the fundamentals of environmental health seem to have gone nowhere. One reason may be that the science associated with environmental matters is complex, disputed, and uncertain. With complexity and uncertainty prevalent, the emphasis is sure to return to straightforward public health pursuits, which focus on measurables (testing) and controllability (social distancing).

COVID-19 and aerosols

COVID-19 has thrown a spanner in the works. It draws attention to the underlying interfaces that humans have with

• The air
• Water
• The built environment
• Vector-borne disease (pathogens).

The evidence for COVID-19 outbreaks is that they are all, or mostly, associated with the indoor built environment. The virus is transmitted from person to person indoors. Further, we know now that the contagion can travel within aerosols. This is possibly the main means of contagion rather than from droplets.

Aerosols are particles that are small enough to be invisible, yet remain suspended in the atmosphere for long periods; they actually behave as if they were dissolved in the air, and the drag forces such as gravity essentially have little or no influence. Such aerosol suspensions in the outdoor ambient are quickly dispersed due to temperature, evaporation, wind effects, solar UV and general outdoor air factors. Not so indoors.

The built environment

In the indoor environment, which is essentially stagnant, settling of aerosol is only influenced by substantial air movement as may be created by openable windows and doors, and by exhaust fans. The aerosol is otherwise free to move according to air drifts and drafts such as gaps under doors – but also those far-less-obvious places such as around wall-mounted power points or along plumbing risers.

Tests with Drager smoke tubes in Beijing during the SARS crisis found such airflows explained how a patient in a hospital on another floor from that of an index patient caught the disease. The Australian experience suggests that the hotels used for quarantining purposes could also be a type of built environment with such invisible pathways.

It would be prudent for quarantining facilities to allow copious air exchange with the outdoors, preferably by use of verandas and wide-opening doors to them; otherwise the use of purpose exhaust fans should be satisfactory.

In Beijing at the time of the SARS crisis the most successful quarantine hospital was one in which all patients with SARS were separated, the air conditioning system comprised a tempering supply ductwork arrangement to each room, and each room provided with a simple exhaust fan to maintain negative pressures. Aerosol discharges from patients are thereby moved to the outdoors and to the natural environment for removal.

Because aerosol particles take the line of least resistance, it is the drafts found at most buildings that would determine flow direction – rather than air movements from a conventional air conditioning plant. One unfortunate (in this context) objective for conventional air conditioning is to avoid uncomfortable drafts by ensuring air velocities are low.

Although all buildings differ in their features, an understanding of the behaviour of aerosols in the built environment should assist with designs to prevent illness. This is especially the case for those buildings of a public nature in which infected individuals may be present, and their airborne discharges may be contagious.

As a component of environmental health, the built environment is seen as the prime preventative focus for ensuring public health is maintained. Indoor air quality is at the heart of the fight to handle COVID-19, but the manner in which that knowledge is used is central to solutions. It includes an understanding of the role of aerosol suspensions and their characteristics. For best public health it is in the sphere of environmental health that the appropriate solutions may be found.