COVID-19 cases slow a little in Australia

Posted onAuthorIan M Mackay, PhD (EIC)14 Comments

Our borders have been shut to non-citizens for about a week and despite being regularly admonished for being terrible at obeying confusing, constantly changing or poorly communicated new rules, the past few days have seen some signs of slowing in Australia’s COVID-19 numbers. Let’s explore this clear change in the pattern a little further.

A few quick facts

The average incubation period – the time from infection to showing symptoms – is about 5 days. The whole range is between 2 to 14 days.

Our national borders were closed to travellers from 20th March. As I write this, that deadline was about one week ago.

Most cases in Australia – nearly two thirds – have been introduced via infected travellers.

Most Australian cases for which information is available, have originated in infected travellers arriving in Australia from overseas. If that balance shifts to become about local transmission – with or without a link, we enter a new phase. Physical distancing within Australia combined with inhibiting travel from outside Australia can eliminate both sources/ We should be seeing some impact now on travel-related case numbers. And we may be. Source: The excellent ABC COVID-19 numbers page.[1]

By my rudimentary calculations, we should now be seeing an impact on the case numbers. And it looks like we could be.

Are total Australian cases slowing?

For the past five days – the numbers have either increased by a smaller amount than the day before (23rd, 24th and 25th) or they have decreased compared to the biggest days (26th).

  • 🙄The next day…
The previous five days saw slowing of total daily numbers. On March 26th and 27th, a drop in daily totals occurred from a peak daily number on March 25th. This is the first time we’ve seen such a consistent slowing since case numbers really took off around 13th March. It’s too early to say a lot, but any change in a pattern like this has meaning; whatever that may be.
But as you cans see, the day after this blog post saw a record number of cases reported by New South Wales and Victoria.
Source: The excellent ABC COVID-19 numbers page.[1]

To be clear – this could be just a bump slowing the journey of a very long road. I’m not saying Australia is done and dusted or that we should relax even a little bit yet. In fact – seeing thing do nothing is exactly what we want! But this could be a sign that border closures have impacted what has so far been the biggest known source of COVID-19 cases; infected travellers arriving from overseas.

The other source that we need to know more about? Cases spreading within the local community with no known links to infected travellers.

How sure are we about this local community transmission thing?

We have heard much about Australia having very little sustained or widespread local transmission of SARS-VoCV-2 out in the wider community, away from travel-related cases and their contacts. But until recently, testing mostly targetted those groups plus the elderly and those in a hospital with unexplained pneumonia. We may have been missing lots of locally transmitted cases. Right?

Maybe not.

Hospitalisations

We haven’t seen lots of new severe respiratory disease cases turning up in our hospital. Even if severe disease represents perhaps less than a fifth of COVID-19 disease outcomes, we’d still expect to see the number in hospital grow in proportion to any widespread local but noticed (or cryptic) transmission.

As far as I know, we haven’t seen that happening.

Deaths

We also haven’t seen any spike in deaths. This one is a bit more problematic as death can take weeks to occur so there is an expected lag between a case being detected when ill, and that person dying if they do. A death today could have been from an infection happening more than a month ago. So we will probably see among the bolus of cases we’ve recently had, around 1% die (just going by one f the more common predicted and adjusted figures).

We’ve had cases in Australia since late January. As of today, we have 13 deaths and 3,177 cases – 0.4% of cases dying doesn’t suggest we had a lot of missed cases early on. But we do need to keep watching that as a lot of cases have occurred in a short and recent time.

Iran is reporting that 7.6% of cases have died, Italy 10.2%, Indonesia 8.7%, Philippines 6.3% and the United Kingdom at 4.9%. On the other end of the spectrum, the United States has so far seen 1.5% of cases die, South Korea 1.4%, Germany 0.61% and Singapore 0.29%. Of course, these could also swing upwards at any time, becoming worse if healthcare services become overwhelmed.

A surge in deaths beyond the expected 1% or less of all cases, could be the canary in the coalmine; the indirect measure of danger due to large numbers of undetected cases.[5]

But these are the main reasons to think that unseen or cryptic spread isn’t happening to a large extent in Australia. Good news if true!

It will be happening to some extent because it has everywhere. But our new measures to prevent the entry of so many travellers into Australia should help keep numbers down, as have our rapid and flexible testing approaches. China has also now restricted travel into the country except by returning citizens.[4] Perhaps we are all learning from each other.

The asymptomatic and presymptomatic conundrum

We have read about cases being tested when they have no signs or symptoms of COVID-19 and also milder cases that get missed possibly.[2,6-9] When they do get tested, it’s often because they were close contacts and usually we see this as part of a written-up scientific study. Some of these people remain asymptomatic but test positive for a short time.

NOTE: I’ve been told in the past by those who look after asymptomatic cases (not ill but tested positive), that if you look hard enough, many will probably have a very short temperature spike, headache, feel a bit hot or unwell etc. The sort of thing that might not be recalled but could be noted at the time.

The rest are in a presymptomatic phase; they will go on to develop illness of varying severity.

We know it is possible for those in either group to host infectious virus in their airway, so there is some risk for transmission.[2] But whether they are a big source of unseen or unnoticed spread of SARS-CoV-2 still seems hard to nail down in Australia.

With more relaxed testing guidelines (see below), we’ll soon learn whether Australia has missed a significant portion of infections, or has remained ahead of the virus. Right this minute, it looks more like the latter.

Australia’s testing criteria were relaxed in some important ways, 26th March.[3]

This isn;t the end of things in fact, if this trend is real, its happening because of some of the most unfamiliar, unexpected and fairly surreal changes made to our way of life. These changes will need to stay in place for many weeks or else that peak will just bounce straight back up. It may still bounce up if we do start to see local transmission take hold.

Everbody’s eyes should be on these daily bars – we want them to keep going down. At the very least, to stop going up.

Time will tell. In the meanwhile – wash your hands more than you do, don’t touch your face until you do and stay physically – but not socially – apart from each other.

References

  1. Charting the COVID-19 spread in Australia
    https://www.abc.net.au/news/2020-03-17/coronavirus-cases-data-reveals-how-covid-19-spreads-in-australia/12060704
  2. Evidence of SARS-CoV-2 Infection in Returning Travelers from Wuhan, China
    https://www.nejm.org/doi/full/10.1056/NEJMc2001899
  3. National Cabinet Update. Media release 26 Mar 2020 Prime Minister
    https://www.pm.gov.au/media/national-cabinet-update
  4. China reports deeply disturbing coronavirus development
    https://7news.com.au/lifestyle/healthmedicine/china-reports-deeply-disturbing-coronavirus-development-c-765460
  5. https://www.flickr.com/photos/jocelyn777/8724420354/in/photolist-ehWWdA-8uSL86-8uSLf2-8aHKeW-4C6ZwQ-9DLNoz-ehWuEw-9DLMXx-8uVP9C-8Hrvih-8mJwKh-8BC69q-8eYqB-8oVUxg-8BC6sw-7XSZVY-8N2FL4-9E2oq6-8N2FHg-9agSem-9agUBb-9adGSD-cKeQrQ-oW4GTz-aQtLi2-8Mnef4-98XnAJ-98Ye2f-4C2Gmc-98Ye2m-7s1Yri-p6751q-8Le5AG-8E1A1A-98XnAN-cKAQXb-8Y1pp1-q7qNG2-oSMCMn-8uVNVY-a4Bcaa-oQDvnE-98XnAQ-8uSLcM-8sS4v4-8FEzYb-8uVPfU-9Y3bpo-98V95B-98VcKH
  6. Estimating the asymptomatic proportion of coronavirus disease 2019 (COVID-19) cases on board the Diamond Princess cruise ship, Yokohama, Japan, 2020
    https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2020.25.10.2000180
  7. Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China
    https://www.ncbi.nlm.nih.gov/pubmed/32146694
  8. Presumed Asymptomatic Carrier Transmission of COVID-19
    https://jamanetwork.com/journals/jama/fullarticle/2762028
  9. Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV2)
    https://science.sciencemag.org/content/early/2020/03/24/science.abb3221.abstract

14 thoughts on “COVID-19 cases slow a little in Australia”

  1. Nice to see some positive news. I know its early but I realised this a few days ago but NOONE reported it?

    Weird.

  3. This account does not cover community transmission at all. The real story was told by the UK Daily Mail and is now, slowly, being picked up by Australian media. Until now, the shape of the curve in Australia has been dominated by the influx of cases by air and sea and measures taken in the community are irrelevant to these changes. We had a bulge. Now we’re moving into the real curve. Community restrictions take about 13 days to begin to show an effect, so come back in a fortnight. Save the sanitizer for your hands.
    https://www.abc.net.au/news/2020-03-31/coronavirus-community-transmission-on-rise-in-nsw/12103390
    https://7news.com.au/lifestyle/health-wellbeing/the-coronavirus-trend-everyones-worried-about-c-770807

  4. Death rates (correct term “case fatality rates”) are underestimated during epidemics due to the time lag between testing for cases and time to death. In Hubei Province the case fatality rate looked to be 2% during the peak of infection but the slowing of new cases and the continued increase in deaths saw the case fatality rise eventually to 4%. The case fatality rate in Spain and Italy will similarly rise over their epidemics and are likely to reach 20% in Spain, 17% in Italy, and up to 15% in the UK and Netherlands. These data are publicly available and simple to analyze.

      1. Hi Dave, Asymptomatic cases are not cases of COVID-19 (the illness). If you mean infection by SARS-CoV-2 then this rate is called the Infection Mortality Rate and is a different measure to Case Fatality Rates.

  6. Could a COVID 19-like corona virus have previously circulated in Australia. Herd immunity against that virus would potentially explain the very low number of reported cases and deaths due to COVID 19 in Australia. Unless the numbers in Brisbane, Sidney and Melbourne are more like New York and Philadelphia, then empirically something very different seems to be occurring in Australia. Best wishes – stay well.

    1. We had testing rolled out and in use on infected travellers almost immediately. We have exemplary contact tracing and isolated the ill. We’ve been constantly refining isolationism as well and then closed our borders. Australia couldn’t be more different from how the US started off.
      It’s not impossible that a related CoV circulated but if it did it didn’t cause noteworthy disease and there’s been no sign of it using serology methods so far – that I’ve heard of anyway

  7. Australia’s border controls focussed on Asian germs until 11 March when Italy was added to the travel ban list. By then the epidemic in Italy had far exceeded the circumstances when Iran and then South Korea were targetted by our travel bans. The Commonwealth Department of Health weekly surveillance reports on COVID-19 show from testing of travellers that the large majority of cases arriving from overseas in early March came from the US and Europe not from Asia. Those reports are publicly available on line. Check out Report 7:
    https://www1.health.gov.au/internet/main/publishing.nsf/Content/novel_coronavirus_2019_ncov_weekly_epidemiology_reports_australia_2020.htm

  8. I think Australia has done a good job at reducing the number of cases. It’s so funny reading books or watching movies about disease during this time. We watched World War Z the other day, which was surreal.

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