Australia is now entering its 12th week since the first cases of COVID-19 occurred in late January 2020. The infection and mortality rates around the world have been extraordinarily variable with epicentres occurring in places like northern Italy, Spain and the UK in Europe and, of course, the major epicentre in New York. Australia, on the other hand, despite a number of warnings from so-called health authorities suggesting we would have 15 million cases and 150,000 deaths, despite being in the same timeframe as the other areas  mentioned, has experienced less than 7,000 cases and just over 50 deaths.

Since the onset of the virus in this country, It has been my opinion that we would not experience the same degree of infection rates or deaths as seen in other countries for a number of reasons. Firstly, I must say that I do agree with the vast majority of social isolation methods introduced by the government. But I have stated on a number of occasions in the media and in my articles that I believe there should’ve been a demarcation between those people who are healthy below the age of 60 and for those of us over the age of 60. The healthy people below the age of 60 should probably be engaging in their normal activities apart from large congregations of people, such as seen at sport, concerts or events such as the Sydney Royal Easter show.

In my opinion, smaller venues such as restaurants and cafes should be opened but with a restriction on numbers, with definite social distancing laws such as the 1.5 metre rule. But I believe it is clear from the accumulating evidence that the major cause for severe disease is “viral load” (defined as the amount of viral particles per ml) or the other circumstance being disease in the elderly or people with poor immune systems. Firstly, to discuss the concept of viral load – this is purely the dose of virus you receive. For example, health workers being exposed to patients with COVID-19 are receiving a much bigger dose of virus as they are caring for very sick people in intensive care units who  are distributing a huge viral load into the atmosphere. Unless there is extremely good ventilation systems to improve air circulation, the virus is being recirculated in a huge dose. Without very strong personal protection equipment, the health workers are clearly exposed. If you are a younger, healthier person with a robust immune system, despite this, a huge dose of virus may overwhelm your healthy immune system and make you very ill. I believe this is why some younger people are still succumbing to the illness.

But if healthy younger people, such as children, are exposed to a lesser dose of the virus, their robust immune systems will mop up the virus quickly and they will either not even appear sick or have a minor infection that clears within a few days. If this happens to a large portion of the population who are healthy, we will see herd immunity kicking in and the virus dwindling off rather quickly.

So we need to ask the question: why is a place such as New York experiencing such huge infection rates and very high death rates? Again, this comes back to viral load. If you look at the average population density of New York City, this is just under 26,500 per square mile, with Manhattan being just under 70,000 per square mile. To compare this to greater Sydney, we have around 1,100 people per square mile and even the inner city around 39,000 people per square mile, with inner-city Melbourne around 53,800 people per square mile.  The reality is that the population in New York City on any working day during the week, before coronavirus hit, could be up to 25,000,000 people, whereas in Australia the numbers are nothing like this. It is this heavy concentration of human beings in the one area that markedly increases the potential for viral load i.e. it's a simple matter of dose. I make the rather weak analogy that if you drink a glass of wine with a meal, that's just called being civilised and it won't hurt you. But if you drink a bottle of whisky on a daily basis, you are really heading for health problems. It's all about dose!

We have seen a resurgence of cases in Singapore over the past week. Up to this point, Singapore was the poster child for coronavirus control. But there have now been 200 new cases reported in the last few days. The headlines suggested Singapore was battling a fast moving second wave of infections. The reality is, to date, a densely populated city-state of 6 million people has only experienced just over 2,000 cases, with seven deaths. Interestingly, and reinforcing my point, the hotspots of infections in Singapore are in massive dormitory complexes housing mostly South Asian workers from places like Bangladesh and Sri Lanka. The cases from these hotspots total a quarter of all the cases in Singapore.

I also reviewed an interesting article that examined how building design can influence disease transmission. It is logical to me that large housing complexes with shared air conditioning units can't be healthy because of the potential for viral droplets being transmitted through these huge, shared, air conditioning units. Long before coronavirus reared its extremely ugly head, we have been well aware of the potential for Legionnaires disease to occur in air conditioning units. The article suggests simple suggestions for healthier buildings including the ability to open windows (wow, that’s a shock) to improve air circulation and opening blinds to admit natural daylight. To directly quote this article “whilst more research needs to be done on the effect of sunlight on COVID-19 indoors, daylight exists as a free, widely available resource to building occupants with little downside to its use and many documented health benefits”.

There is no doubt that the main transmission of coronavirus is person-to-person but we are also well aware of the potential for the virus to settle on surfaces, with some estimates from anywhere between a couple of hours to a few days, depending on the surface. Virus particles are too small to be blocked by standard air filtration strategies and interestingly humid conditions may help control the virus, which is another reason why we are seeing less disease in very humid environments.

It is important to reinforce the vital importance of regular hand washing and regular cleaning of services where many humans are touching and being exposed to these surfaces.

Of course, the holy grail for the control and management of COVID-19 is to find an effective vaccine and also effective antivirals that will treat the more severe cases. Researchers around the world are frantically working towards both of these means. In the meantime, it is vital we continue to practice social distancing, reduce our exposure to large crowds, regularly wash our hands and ensure common surfaces are regularly cleaned. The disastrous consequences to our economy and whether China should be compensating the rest of the world for introducing this virus to the planet, is a topic for other people more expert than myself in these areas but is certainly an ongoing issue that needs to be discussed.

Leslie Dietz et al, 2019 Novel Coronavirus (COVID-19) Pandemic: Built Environment Considerations To Reduce Transmission, mSystems (2020).  DOI: 10.1128/mSystems.00245-20