If you live in a major city when do you want to start panicking about COVID-19 Allan Greenwood Follow Mar 17 · 10 min read

Disclaimers upfront!

I have a background in data analytics with a formal education in Physics. I have utilized public data and sourced hard facts where available and called out assumptions when the data is not available. This is an educated opinion and has not been peer reviewed.

Edit. New South Wales has announced a lock down just in time. They are locking down on the 24th of March. On the 21st they had 83 confirmed cases. By Tuesday under current growth this will be at around 160. The trigger talked about in this article was 320 cases for Sydney and with the under testing in Australia they are probably hitting this tipping point.

Summary

COVID-19 has a substantially different mortality rate when you get hospital care vs when there is no hospital care.

The mortality rates being discussed in the popular media is assuming hospital care but like what was seen in Wuhan and now Italy this virus will overwhelm hospitals.

My view is that we should start panicking about a lack of government action before the hospital system starts failing due to a lack of ICU beds for new coronavirus cases. It is not helpful to be panicking before this point as both personal risk and societal risk is low. Social Isolation works we just need the authorities to have the courage to implement and enforce.

The article has lots of mathematics and in many cases an unfortunate need for assumptions but if you want to skip all the fun bits then the answer for when to panic is

· For Melbourne or Sydney when there are between 300–800 cases a day (Assuming a reasonable level of testing is being carried out). If you do not trust the testing it is when daily deaths reach the 6 to 12 level per city.

· For other regions it is 1 to 2 deaths per 1,000,000 population or 60 to 160 daily cases per 1,000,000 population. Note hospital capacity varies by country so this ratio is not perfect elsewhere in the world.

For Australia my guess is that Sydney is at least 2 weeks away from this point and probably longer with the recent banning of gatherings of 500 or more people. Melbourne is even further away as there is very little community spread being identified and Queensland is in between the two.

Incidental this level of virus penetration is about the level when Italy or more precisely the Lombardy region went over the cliff in regard to hospital resources even though they did not realize it for 5 days. On the 15th of March when Spain and France entered full lockdown, Spain was at this tipping point and France a week away.

Before this tipping point if you suffer the 1 in 10,000+ event that results in you personally catching the virus (or any other condition requiring ICU) there will be medical care available to treat you. For reference being killed by a car as a pedestrian is a 1 in 70,000 event in NSW.

Analytical Approach

This analysis paper will look at SARS-COV-2s impact on hospital as a proxy for when extreme social isolation action like China, Italy, France and Spain is required. I will be using publicly available information to look at what point a SARS-COV-2 epidemic in Australia is likely to start resulting in increased mortality rate due to patients not receiving the required medical resources.

This whole exponential fatal disease problem reminds me of the old Mathematics problem, where you are presented with the statement of.

There is one lily pad in a lake, and it doubles everyday till it finally fills the lake after 28 days.

You are then asked.

How many days does to take to fill half the lake?

The answer of course is 27 days (at which point there are 67 million lily pads). In the same situation if I asked how long it would take to fill 1 percent of the lake most people would not know. 1 percent fills on the 22nd day. Basically, you have a slight lily pad problem right up till the entire lake is filled with them.

That is what this epidemic is like. Melbourne or Madrid or Manila will have cases occurring without overloading hospitals and everything will be under control and then it will all fall apart when suddenly the cases and the load double after 5 days and then go catastrophic 5 days later when it doubles again and then…. Well hopefully the government can do something before then.

How SARS-COV-2 presents

Asymptomatic (IceBerg) infections will be ignored in this analysis due to insufficient hard data. If they existed, the extensive testing carried out on Diamond Princess should have identified them, but a study of symptom expression indicates that the true asymptomatic rates is as low as 19 percent. If this is the case, then all death rates out of china should be reduced by at least 0.8. There is also the possible of mild symptoms not being picked up in the China data which may reduce the china death rates further.

Iceberg cases are not pertinent to this analysis as true iceberg cases are unlikely to be picked up by the scattered testing approach being deployed in most countries around the world.

How Cases Can Overwhelm Hospital System

Due to exponential growth at some point the number of cases requiring hospital resources will exceed the “mostly” fixed capacity of the hospital system. When this happens there will be deaths that would otherwise be avoidable.

The above graphs are illustrative only

Medical treatment capacity

There are two different measures you need to look at in estimating health capacity.

1) Hospital beds

2) ICU beds / Ventilator beds

From OECD statistics Australia has 92,000 hospitals beds.

ICU bed numbers are harder to track down. Experts have quoted a figure of 6000 ICU beds in newspaper articles. Separately I have tracked down an academic study for 2005/2006 that identified Australia as having 5100 ICU & ventilator beds. This number seemed low and I double checked vs an Australian Institute of Health report in 2017 that indicated that man days equivalent to 1742 ICU beds were charged meaning that a 5100 estimate should be on the high side of capability.

For the purpose of this analysis I will be scaling the bed numbers from 2005 to reflect population growth. I am comfortable with using this estimate of 6500 as overall spend on health over this time has outpaced inflation and I see no reasons for the relative number of ICU beds to have decreased.

ICU beds is the important measure as they will be the bottle neck before hospital beds based on the SARS-COV-2 statistics from China.

EDIT. Australian newspapers are reporting we have just 2229 ICU beds. I know for a fact that considerable expansion of ICU is currently occurring that is pushing this number up. Overall I am confident with the analysis to date and in the table below the 15 percent capacity (using 975 beds is probably where you want to focus on)

Impact on health care professionals.

It needs to be acknowledged that during pandemic in Australia the health practitioners are going to be hard hit by SARS-COV-2. When this occurs capacity in the Australian health system will be reduced above and beyond physical ICU capacity. When health care staff gets sick the availability of medical resources will decrease. Conversely in an emergency situation medical staff will work overtime, old beds can be used and retired nurses and doctors can be drafted back which may enable some additional capacity to be realized. How these two impacts play out is unknown and I have not attempted to address them beyond this note.

Tipping point

Tipping point represents the point where percentage of new virus cases in the community generates ICU cases equal to the number of ICU beds being released due to recovery and deaths from the Virus. Any additional cases beyond this number will not have an ICU bed available and will almost certainly die due to the lack of resources. Basically, with the bed you have a chance of survival without the bed you will definitely perish.

How long are ICU beds required for

SARS-COR-2 generates a need for ICU capacity as we see hospitals being overwhelmed in both China and Italy. Within China 4.7 percent of patients required intensive care. However, the number of patients is not on itself sufficient for estimate purposes we also need to know how long the patients used the bed for. For this I have used published studies from the previous SARS outbreak given similar progression observed between the two diseases. SARS patients that required intensive care needed their ICU beds for a median of 8 days.

Calculation of number of daily cases Australia can support

Anecdotally I have seen estimates of excess capacity in intensive care of between 10 and 25 percent. Without a definitive source I have decided to estimate 10, 25 and 35 percent spare capacity as pinning exact excess capacity is difficult.

The following table shows the logic used to calculate the number of cases a given number of available ICU beds can support.

Calculating Australian Capacity to Absorb SARS-COV-2 Cases

We can validate this against Italy experience. Italy anecdotally ran out of medical capacity around the 9th of March.

I do not trust Italy case numbers as they have only been testing serious cases however their death numbers are most likely accurate. Italy on the 9th of March had 640 deaths comparing this to China Case / death numbers we can estimate the underlying number of cases in Italy.

We can then guestimate the number of cases on the 9th when Italy got into trouble in Lombardy of 4,000 new cases and 2,200 average over the last eight days. Scaling populations to Australian population this would be equivalent to a steady state of ~5000 daily cases across Australia or in our model a utilization of ~30 percent of ICU beds for coronavirus before the Italian system overloaded.

How does this help is work out when to panic?

Our desire is to keep cases below the threshold where all our medical resources are consumed. However as it is a disease multiplying exponentially we cannot wait till this number of cases hit out tipping point number because at that point even if we prevent any new cases by isolating everyone there is still a whole lot of people who have caught the disease and are at the start of their 5+ day incubation period.

In regions/countries without social isolation policies SARS-COV-2 doubles its cases every 5 days we need to factor for this doubling when working out the number cases. A small amount of Mathematics shows you need to introduce extreme social isolation measures when cases are within 58% of the targeted cases to ensure the unavoidable case ramp up does not go over your targeted average case threshold.

For a city of 5 million (Melbourne and Sydney) our panic moment is

Table for when cases in Melbourne or Sydney will result in full use of ICU

There are lots of assumptions made in constructing these estimates. What can be concluded is that between 300 and 750 daily cases in either Melbourne or Sydney is a reasonable time to panic and you can expect the government around this point to introduce extreme social isolation measures to stop growth.

A few other important points

· The difference between 15 percent and 35 percent capacity estimate is large but represents only 8 days of exponential growth. If you panic at the lower number and the higher number is correct you will be panicking only 8 days early.

· At the upper panic point of 750 daily cases you are looking at around 1 in a thousand people (0.1 percent) being infected. Most experts are expecting 20 to 70 percent infectious level.

· A 20% epidemic level in a city/region is therefore catastrophic for health care. Even if you stretch it over six months and assume 2300 available ICU beds over 60 percent of people who need ICU will not get it which will spike mortality rate

· Sydney on the 14/3 had 20 new cases but 7 were from overseas so we have 13 community like cases which may be the start of community spread. Not all cases are being picked up so assuming there are total of 30 new ‘true’ daily cases then Sydney is 18 days away from panic stations.

· If you have read this far please reshare in your social networks as I think lots of other people will find this interesting

· I will update this post as new information becomes available

Policy points I would like to see introduced till vaccine for vulnerable is available

· Intensive Social Isolation introduced whenever a city approaches the ICU tipping point (or earlier). This will be done as often necessary and would be something like the restrictions in place in Italy. (i.e. Work from home and only essential industries keep functioning (Food, Utilities and Medical))

· Heavily restricted air travel with a compulsory SARS-COR-2 test after 5 days in quarantine for all international arrivals from a point where community SARS-COR-2 is rampant.

· I do not believe this disease can be eradicated till vaccinations become available hence policy should pivot to the containment strategy of the above two points

Links and references

Hospital beds and ICU

Total Hospital Beds (2017) — https://stats.oecd.org/index.aspx?DataSetCode=HEALTH_REAC#

ICU Beds Charged (2017) — https://www.aihw.gov.au/getmedia/d5f4d211-ace3-48b9-9860-c4489ddf2c35/aihw-hse-204.pdf.aspx?inline=true

ICU Beds 2005 Study — https://journals.sagepub.com/doi/pdf/10.1177/0310057X1003800124

Time in an ICU bed for SARS

https://www.aic.cuhk.edu.hk/web8/SARS%20outcome.html

https://jamanetwork.com/journals/jama/fullarticle/196917

China Case Information

http://weekly.chinacdc.cn/en/article/id/e53946e2-c6c4-41e9-9a9b-fea8db1a8f51

Cumulative Cases and Deaths

https://github.com/CSSEGISandData/COVID-19