Article Text

Original research
Trends in outcomes following COVID-19 symptom onset in Milan: a cohort study
  1. Christopher H Jackson1,
  2. Francesca Grosso2,
  3. Kevin Kunzmann1,
  4. Alice Corbella3,
  5. Maria Gramegna4,
  6. Marcello Tirani4,
  7. Silvana Castaldi5,
  8. Danilo Cereda4,
  9. Daniela De Angelis1,
  10. Anne Presanis1
  1. 1MRC Biostatistics Unit, University of Cambridge, Cambridge, UK
  2. 2Postgraduate School of Public Health, Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
  3. 3Department of Statistics, University of Warwick, Coventry, UK
  4. 4Welfare General Directorate, Regione Lombardia, Milan, Italy
  5. 5Post-graduate School of Hygiene and Preventive Medicine, University of Milan, Milan, Italy
  1. Correspondence to Dr Christopher H Jackson; chris.jackson{at}mrc-bsu.cam.ac.uk

Abstract

Background For people with symptomatic COVID-19, the relative risks of hospital admission, death without hospital admission and recovery without admission, and the times to those events, are not well understood. We describe how these quantities varied with individual characteristics, and through the first wave of the pandemic, in Milan, Italy.

Methods A cohort study of 27 598 people with known COVID-19 symptom onset date in Milan, Italy, testing positive between February and June 2020 and followed up until 17 July 2020. The probabilities of different events, and the times to events, were estimated using a mixture multistate model.

Results The risk of death without hospital admission was higher in March and April (for non-care home residents, 6%–8% compared with 2%–3% in other months) and substantially higher for care home residents (22%–29% in March). For all groups, the probabilities of hospitalisation decreased from February to June. The probabilities of hospitalisation also increased with age, and were higher for men, substantially lower for healthcare workers and care home residents, and higher for people with comorbidities. Times to hospitalisation and confirmed recovery also decreased throughout the first wave. Combining these results with our previously developed model for events following hospitalisation, the overall symptomatic case fatality risk was 15.8% (15.4%–16.2%).

Conclusions The highest risks of death before hospital admission coincided with periods of severe burden on the healthcare system in Lombardy. Outcomes for care home residents were particularly poor. Outcomes improved as the first wave waned, community healthcare resources were reinforced and testing became more widely available.

  • COVID-19
  • epidemiology
  • public health

Data availability statement

Data are not publicly available. This study is based on a database maintained by the Prevention Unit of the General Directorate of Welfare of Regione Lombardia. The authors can forward inquiries relating to use of this database.

https://creativecommons.org/licenses/by/4.0/

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Data availability statement

Data are not publicly available. This study is based on a database maintained by the Prevention Unit of the General Directorate of Welfare of Regione Lombardia. The authors can forward inquiries relating to use of this database.

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Footnotes

  • CHJ and FG are joint first authors.

  • Twitter @cjackstats

  • Contributors DC, DDA and AP designed the study. FG and AP searched the literature. MG, DC, FG and MT collected the data. CHJ, AP and KK performed the statistical modelling. DC, FG and MT contributed to interpreting the results. CHJ, AP and FG wrote the original draft of the manuscript. AC, MG, MT, SC and AC contributed to revisions of the manuscript. CHJ is the guarantor, accepting full responsibility for the work and publication.

  • Funding This work was supported by the Medical Research Council, programme number MRC_MC_UU_00002/11.

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.