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Modelling the impact of COVID‐19 on intensive care services in New South Wales

Gregory J Fox, James M Trauer and Emma McBryde
Med J Aust 2020; 212 (10): 468-469. || doi: 10.5694/mja2.50606
Published online: 15 May 2020

Coronavirus disease 2019 (COVID‐19) poses extraordinary challenges for health care in Australia. One of the greatest will be the pressure on hospitals to support people with severe disease. Modelling studies can provide valuable insights into the likely course of the epidemic, and can be particularly useful for anticipating resource requirements, including demand for intensive care services at the peak of the epidemic. In this report, we extrapolate the findings of the Imperial College model of the pandemic1 to the New South Wales population. We also developed a simple SEIR (susceptible–exposed/incubating–infected–removed) model to explore the effect of varying the infection reproduction number (R), which can be reduced by effective social distancing measures, on the timing of the peak of the epidemic. The two models are described in the online Supporting Information.

Applying the Imperial College model, the peak demand for intensive care in NSW would be at least 6965 beds if mitigation efforts — isolation of people with confirmed COVID‐19, household quarantine of their contacts, social distancing from people over 70 years of age — are implemented, or almost eight times as many as the baseline number; without mitigation, more than three times as many ICU beds (21 283) could be required (Box 1).

Applying our SEIR model to a scenario without social distancing measures (R = 2.4), the number of people requiring hospitalisation in NSW would peak at 450 per 100 000 population (35 375 beds), and the number requiring critical care at 150 per 100 000 population (11 792 ICU beds, or 1349% of baseline ICU capacity). In this scenario, viral transmission would peak during late June and ICU bed occupancy in early July. About 16% of people would be potentially infectious at this point, although a smaller proportion was modelled as exhibiting symptoms (Box 2; Supporting Information, table 3).

In a scenario of increased social isolation (R = 1.6) and an assumed hospitalisation rate for people with confirmed COVID‐19 of 6.7%, case numbers would peak in early October and ICU occupancy in mid‐November; about 180 people per 100 000 population would require hospitalisation (14 150 beds) and 65 per 100 000 intensive care (5110 ICU beds, or 585% of baseline ICU capacity) (Box 2; Supporting Information, table 3). That is, the peak figures would be about one‐third the size of those in the no mitigation scenario. Sensitivity analyses in which the proportion of hospitalised patients was varied (5–15%) similarly found that increasing social isolation markedly reduced demand (Supporting Information, table 4).

We have used two modelling methods to estimate peak demand for critical care services in NSW during the COVID‐19 epidemic. Both approaches identified that COVID‐19 would impose a major burden on the health care system, and the mismatch between the estimated numbers of ICU beds needed and their availability is stark. Our modelling shows the critical importance of effective COVID‐19 containment strategies, as well as the urgent need to invest in resources that support the surge capacity of critical care services in NSW.

Box 1 – Estimated number of intensive care unit (ICU) beds required at the peak of the initial wave of COVID‐19 cases, applying the Imperial College model to New South Wales, by Local Health District (LHD)

 

 


Mitigation strategy


Population (2016)2

No mitigation

Close schools, universities

Case isolation

Case isolation, household quarantine

Case isolation, household quarantine, social distancing of people over 70


ICU beds needed per 100 000 population1

275

240

190

125

90

ICU beds need, by LHD

 

 

 

 

 

 

 Sydney

656 460

1805

1576

1247

821

591

 South Western Sydney

964 342

2652

2314

1832

1205

868

 South Eastern Sydney

914 021

514

2194

1737

1143

823

 Western Sydney

948 584

2609

2277

1802

1186

854

 Northern Sydney

914 233

2514

2194

1737

1143

823

 Illawarra Shoalhaven

405 534

1115

973

771

507

365

 Central Coast

335 309

922

805

637

419

302

 Other LHDs

2 600 791

7152

6242

4942

3251

2341

All NSW (proportion of baseline bed number)*

7 739 274

21 283 (2435%)

18 574 (2125%)

14 705 (1682%)

9674 (1107%)

6965 (797%)


 * Estimated number of ICU beds prior to COVID‐19 epidemic: 874.3

Box 2 – The estimated number of patients with COVID‐19 admitted to hospital or to intensive care units (ICUs), according to a SEIR model of the epidemic


* For main curves, 10% case hospitalisation rate assumed; shaded areas show range for hospitalisation rates between 5% and 15%.

Received 22 March 2020, accepted 16 April 2020

  • Gregory J Fox1,2
  • James M Trauer3
  • Emma McBryde4

  • 1 Sydney School of Medicine, University of Sydney, Sydney, NSW
  • 2 Royal Prince Alfred Hospital, Sydney, NSW
  • 3 Monash University, Melbourne, VIC
  • 4 Australian Institute of Tropical Health and Medicine, James Cook University College of Medicine and Dentistry, Townsville, QLD

Correspondence: greg.fox@sydney.edu.au

Competing interests:

No relevant disclosures.

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