Hospitalisation rates differed by city district and ethnicity during the first wave of COVID-19 in Amsterdam, the Netherlands 2 41 Health and the Environment (RIVM). In the wider region of Amsterdam-Amstelland, all positive cases are notified to the regional PHS of Amsterdam. For this study, we retrieved secondary data collected between 29 February (date of first confirmed case) and 31 May 2020 from the Amsterdam-Amstelland COVID-19 notification database, the surveillance database by the PHS of Amsterdam on all notified cases, hospitalisations and deaths residing in the municipality of Amsterdam. These data included information on age and sex of the case, and whether the case had worked as a health care worker or was a resident in a long-term care facility. We matched surveillance data to registration data from the municipality records of the City of Amsterdam (BRP) to retrieve postal code and the country of birth of the case and their parents. Since this study made use of routine surveillance data, no human participants were involved. The database is not publicly available. Determination of city district and migration background We determined city district based on postal code of current residence(14). We assessed migration background and generation based on the country of birth of individuals and their parents(15). Dutch ethnic origin, i.e. having no migration background, was defined as having parents who were both born in the Netherlands. An individual was considered of non-Dutch ethnicity if he/she was born abroad and had at least one parent who was born abroad (first generation) or he/she was born in the Netherlands and both parents were born abroad (second generation)(16). For second generation migrants of whom both parents were born abroad, the mother’s country of birth was leading in defining migration background. Individuals of non-Dutch ethnicity were further classified into having a non-Western migration background (from African, Latin-American or Asian countries, or Turkey, excluding Indonesia and Japan) or Western migration background (from North-American, European or Oceanian countries, or Indonesia or Japan, excluding Turkey) according to the definition of the Dutch Central Bureau of Statistics(16). Statistical analysis We evaluated the number of cases, hospitalisations and deaths, overall and over time (notification date and symptom onset). In the epidemiological curve by self-reported date of symptom onset, missing dates were imputed, assuming that all those who were tested had symptoms. First, we created a distribution of time between symptom onset and case notification for those with a known date of symptom onset. Second, we randomly sampled from this distribution to estimate the date of symptom onset if this was missing.
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