Air is not “the new poop”, Covid is not cholera

Equating the transmission of waterborne and airborne pathogens is beguiling but wrong

The new-found interest in airborne transmission following the emergence of Covid-19 is welcome. It provides new impetus for focussing more on building ventilation and improving the quality of the air we breathe, especially when indoors. It brings all kinds of benefits beyond simply reducing risks of disease transmission.

The enthusiasm has however in some cases gone too far, including comparisons between the provision of clear water in the elimination of many waterborne diseases, to being able to eliminate transmission of airborne pathogens in the same manner.

“Air is the new poop”

I am sorry to say this is incorrect.

Why can we control waterborne transmission?

Pathogens which are transmitted through water almost invariably follow the same path. They enter water through faeces (poop). Someone later ingests the water which someone has pooped in. That person is now infected, and when they poop into some water, the chain continues.

We can control this by cleaning water. Since we can control the source of drinking water, we can ensure it has been cleaned of any poop which may have contaminated it. We can also provide separate, contained sources of water for people to poop into (sewage) and keep this completely separate from drinking water.

We can do this because for waterborne pathogen transmission, the processes of contaminating the water (pooping) and ingesting it (drinking) are both discrete. For a few defined episodes a day, you drink, or you poop. If you need water, you can make sure you only drink it from a clean source. If you need to poop, you can make sure you only do it in a place where it will not contaminate clean water.

Because the processes of contamination and ingestion are both discrete, you can control where they happen and separate the sources.

Why can’t we control airborne transmission?

The issue with airborne pathogens is that the process of both “ingestion” of the source (breathing in) and “contamination” of the source (breathing out, laughing, speaking, shouting, etc) are continuous.

I cannot control the source of my air, because I have to breath whatever air happens to be around me wherever I am. In the same way, I cannot control what air I “contaminate”, because I have to breathe out, speak etc wherever I am at the time.

If I improve ventilation, I can control the speed at which contaminated air is replaced or diluted, but if someone else is close to me at the time they will get exposed regardless. Similarly, if I am filtering contaminated air, it may often need to pass by someone else on its way to the filter.

High quality, well fitting masks can reduce this risk if worn appropriately in a given setting, but masks have to come off sometimes, and we have to keep breathing even when they do. Masks also cannot be worn during some of the highest risk activities for transmission, like when eating, drinking and socialising.

The poop pool

I apologise in advance for this analogy. If you are eating, I suggest you come back to it later.

To properly compare Covid-19 to waterbourne pathogens such as cholera, it would be the equivalent of everyone living in swimming pools, and continuously pooping and drinking the water in the pool. Even with the most efficient filtration/decontamination systems in the world, you cannot prevent yourself from ingesting poop. Worse, if you want to speak to someone you will almost certainly have to poop on them.

I apologise once more for this analogy.

That is not to say we wouldn’t want good provision of fresh water and cleaning of our water - these things will obviously help. But clearly we cannot gain complete control over transmission in this setting.

If you think this analogy is stupid, I agree - which compounds the point that airborne diseases are not analogous to waterborne.

Stigma

There is another reason we should avoid these comparisons. There is a clear social, and biological necessity for privacy when pooping. This is driven by the need to prevent disease transmission. You do your business away from other people. Contaminating other peoples water is, rightly, highly stigmatised.

Because airborne transmission occurs predominantly during socialisation, we risk directly stigmatising socialisation by equating “dirty water” with “dirty air”. As a public health message we can easily cause increased anxiety by making people feel as though they risk exposing themselves to “dirty air” when socialising, which as discussed, cannot be avoided due to its continuous nature of contamination and ingestion.

Humans are innately social creatures. Excessive anxiety associated with basic human needs is deeply harmful to wellbeing and mental health. We can promote the benefits of healthy air without stigmatising socialisation.

Summary

Engineering solutions eliminated many waterborne pathogens from high income countries. It is not possible to achieve the same thing for airborne pathogens, due to the continuous processes of both ingestion and contamination.

However, we can substantially improve the quality of the air we breathe through engineering processes, and this can reduce the likelihood of transmission in these settings. In addition, improved ventilation has health benefits beyond disease transmission which make it worthwhile.

Improving ventilation and air quality should be much higher up the priority list, and would help in reducing illness from airborne disease - but we must be realistic about what it can achieve. We cannot end the pandemic with improved ventilation.