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

Abstract

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). 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 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). 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%. 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. Competing interests No relevant disclosures. Supporting information Supplementary methods and results Click here for additional data file.