The gap is in the epidemiology of the COVID-19 disease, so far as it affects people in the general population. Three months of experience, some hard-gained, has taught us a good deal about the aetiology of the viral disease - how it is caught by an individual, progresses into a disease, and is best treated according to the symptoms demonstrated.

But we still know very little about how the disease moves around the general population. We can generalise, up to a point, from what we have seen about those who got infected. But what have we learnt from those who were not? Until we have a more thorough understanding of the dynamics of the disease in cities, suburbs, towns and rural populations, our capacity to get the best value for money from the measures we have adopted is compromised.

Getting a good epidemiological picture involves testing the general population, including those we have no reason to believe are infected. And, probably, doing it on several occasions, to see how the incidence, prevalence and severity varies over time.

Such studies are critical to proper management of the risks to particular populations - such as Indigenous Australians in remote settlements, or, indeed, on the fringes of our capital cities. Or in assessing risks and strategies for the mobile older population, and for pre-schoolers. We cannot fashion strategies simply from what we know about hospital cases.

European nations appear to be so overwhelmed by active cases that they have had little opportunity to see the COVID-19 presentations in context. The Chinese have begun publishing some papers on their experience - and with a good many properly expressed reservations about their data - but most of their material depends on their experiences with people, or groups (such as young people) who got sick. In China, lots of people got sick. But lots did not, whether because of quarantine or other active measures designed to reduce the chance of exposure, or, perhaps because the disease simply did not take. As yet we have no understanding of why some won and some lost.

Although the Australian incidence is rising, the prevalence is still small. We must keep sufficient screening tests for those presenting as sick, but we now have the time, and the scope, for extensive latitudinal and longitudinal studies among different populations, temperature zones, and social groups. And even if most Australians are, in theory, following similar rules designed to reduce exposure, there might be scope too to look at the impact of particular containment regimes.

Some other countries which ought to have been well placed to conduct epidemiological studies will inevitably be badly behind our capacity. The US was very slow to get going, and, although the number of cases is beginning to mount, in part as a consequence, still has no real idea of how bad the problem is. That is because of serious shortages of testing materials, and failures to do proper testing of many early cases presenting with acute pneumonia conditions, a good proportion of which was almost certainly COVID-19. Likewise, Britain lost the plot for a while, in part because of the chaos, disorganisation and indiscipline of the Boris Johnson government, and in part because of nutty - indeed dangerous - misunderstandings of medical advice about the development of herd immunity. South Korea and Japan have the expertise and the experience to add to the body of knowledge necessary for an understanding of strategies.

As does China. Because the Chinese government is communist and totalitarian, and is seen by some rival nations as being in a dangerous and expansionist mood, there is a tendency for some observers to dismiss anything emanating from China, particularly if it contains statistics, as deeply suspicious, and probably propagandistic if not consciously misleading. COVID-19, or "the Chinese virus" as President Trump calls it, is simply another stick to beat China with. And it goes without saying that the nation's leadership responded too slowly, with too much concern for appearances, and thus, by negligence, allowed the disease to get out of control.

Perhaps, but I am not convinced that it is a total disaster story. Indeed, I doubt that the US (or Australia) would have mobilised as quickly as China, or as effectively, within the time that China did. Indeed the shambles we are still seeing in the US, three months after the first cases, suggests the US was too political, too complacent, and suffered from an anti-intellectual stripping of the capacity, resources and access to power of its systems for dealing with epidemics. As a result, the US is not leading the world in handling the disease, nor in discovering the way out. Indeed, as Australia is discovering, it is now a major source of export of the virus.

China might have been slow to take the people into its confidence, but had notified WHO within weeks of discovering a pneumonia of unknown origin in the Wuhan area. Within three weeks, its quarantine and containment systems had reduced the rate of spread of the disease, and its rate of growth. That's a formidable achievement. Perhaps it might have done better, but its measures have been, so far, better than in most of the first world. And the scientific reviews it has published, as well as the WHO reviews, are credible, and consistent with the experience elsewhere. They do not appear to have been sanitised, or bent to some propaganda purpose.

But even with China, we do not know how the disease spread among the general population, or much about its true incidence. Initially, its focus was on strange new presentations of acute respiratory disease at regional hospitals. In due course, following up of cases led to an understanding that the severity of the disease among those who had it, or were thought to have it, varied enormously.

We know from the aetiologies and published guidance materials that the disease is most severe in older people, particularly those with already compromised respiratory or immune systems, including chronic smoking - and that many younger people, particularly children, seem to survive exposure without showing symptoms, or only very mild symptoms. We are learning, if slowly, about when a patient is infectious - at least, apparently, for a day before symptoms are evident - and how long an ultimate survivor has the virus before it passes out of the body, with, apparently, at least some temporary immunity.

We also know some ways of establishing those people who seem to be most at risk, and about sorting out whether particular symptoms - fever, say, or pneumonia or gastroenteritis - are symptoms of COVID-19 or some other flu or condition. And we can now use serology and other pathological evidence to positively identify the disease. Around the world, scientists, big pharma and other parties galvanised by the disease, or the profits to be made from useful COVID-19 technology, are looking for quicker, cheaper ways of dividing those who have got the virus from those who have not. Others are working on vaccines - a number are already in testing - and others are already testing new drugs which appear to help reduce the intensity, or, it is to be hoped, fatality of the condition.

Around the world, and around the Commonwealth and the states, politicians and public health officials have been making the most of what we know of non-medical means of reducing exposure to the disease. We have quarantined and we have sought to contain; we have sought to isolate active cases, in an acute hospital environment if the disease is severe, or by isolation if infection is only suspected or the disease is not critical. We have urged older people and others at risk to remove themselves as far as possible, usually in their own houses, from exposure to those who might infect them (or whom they may infect). We have attempted to close down large public gatherings and now smaller ones, have closed down many public entertainments, and have urged people to maintain a greater space between each other. We have flirted with, and in Australia so far rejected the idea of closing schools and universities, if only because that would have an immediate effect on the availability of doctors, nurses and other medical personnel. Many of these would be forced into being at home looking after children.

Thousands of Australians with a cough, a cold, or a raised temperature have presented themselves to health officials wondering whether what they have is COVID-19. A good many are turned away without really being tested, in part because the rationing of scarce resources so far has meant that active case-finding is focused on those who have recently travelled abroad, or those who have been exposed to people known to have the virus (usually after being abroad). We can take it that every case of the virus in Australia originally came from abroad, whether the United States (the most likely) or China, Italy, Iran or any other of the many countries where the condition is now pandemic, and to a greater extent than in Australia.

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But here as in the rest of the world, Australia has mostly got the cart before the horse. We really have very little idea of how many people in Australia are carrying the COVID-19 virus. Estimates, based on active conditions, or the daily scoreboard of cases and deaths could be out by a factor of 10 to 50, here as much as in Italy, or Spain, or the United States. That means the "real" death rate from COVID-19 could be anything from 3 per cent to 0.06 per cent - a significant difference.

No one yet, except to a limited extent in South Korea, is actively going out and screening the general population. They are, rather, merely ticking off cases presenting to medical services, and then doing some active (and worthwhile) detective work to find out with whom these victims have been in contact, whether so as to establish new people who may be at risk, or to try to establish who got what from whom.

Meanwhile, it is quite possible that the virus has already moved into the general population, and is now established in particular communities well-separated from those who have returned from overseas. This is the very definition of the word pandemic - that the Australian government used when anticipating the World Health Organisation declaration, and trying, as it thought, to get ahead of the action.

If the community reservoir is among younger people, where many fewer cases have severe or critical consequences, the spread of the disease (at this stage) may not be obvious in the form of critically ill presentations to hospitals, doctors, or drive-in clinics. Though the protective measures have massively heightened public awareness of the symptoms, there has also been considerable publicity about the fact that many COVID-19 symptoms are just like coughs, colds and mild fevers, and are probably just that, particularly if one has not recently returned from overseas or been in contact with a sick person who has. Very few Australians who have presented have actually been clinically tested unless they report travel or exposure to a sick person who has travelled.

Those most closely involved in trying to restrict exposure, and to prevent a hump of serious cases overwhelming critical care and intensive care beds, can be excused, so far, for the relative lack of attention to the epidemiology. So far, we have not had enough testing equipment, and the tests have been expensive and not very fast. It has been natural that they have been rationed out to those most likely to be infected, with a view to getting them, as quickly as possible, to isolation and treatment. When the testing has involved serology, or efforts to establish the actual presence of the virus (rather than, say, an antibody response) it has often been integrated into the treatment rather than the screening regime.

Epidemiological studies could anticipate, rather than follow, even cheaper screening materials. Selective mass screening among particular populations - say of Central Australian Aborigines, or the population of Wangaratta, or the students at the University of NSW - might, for example, collect blood samples as well as other evidence. It might, right now, be too expensive to completely analyse these samples, or they may be lower in priority for analysis than samples among people already diagnosed and fighting for their lives. But gathering the data now would be much more useful than attempting to do it in arrears, or by later attempts to deduce what the antigen load was, based on a few samples.

Sardonic readers, with a well-developed mistrust of politicians and a developing cynicism about the shifting certainties of public health experts, extend their doubts to the commentators as well. How come, one reader asked me in a friendly enough manner, the very same people who were experts four months ago on the drought, and then the bushfires, as well as its connection with climate change, are now writing with confidence about disease control?

It's a fair question. But bear in mind that on almost any such subject, there is an extensive literature. It is one of the duties of journalists - alas, not always taken up - to read and try to understand this material and to summarise it for a public that usually does not have the time. One quickly learns, moreover, that the policy questions they invite are the usual ones of politics - the rationing of public resources, making decisions between different priorities, and applying to issues general philosophies of management, control and accountability. That's far more than scoring the brawls between the players, but it does involve an understanding of competing interests and priorities, and of the calibre of various decision-makers.

For myself, I worked with Professor Fred Hollows in the National Trachoma Program in the late 1970s - when it examined and provided services to more than 100,000 people in about 500 communities around mainland Australia. I helped with the epidemiological analysis of its survey results, and helped write the report. The program also had the benefit of advice from one of the fathers of modern epidemiology, Archie Cochrane, after whom the authoritative Cochrane Collaboration reports are named. This does not make me an expert, but it means that I have read and can understand the literature.

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