Elke Wynberg

General introduction 17 1 COVID-19 in the Netherlands: The first wave SARS-CoV-2 infection was declared a Group A notifiable disease in the Netherlands on 28 January 2020. Classification as a Group A pathogen mandates that both suspected and confirmed cases must be notified, and grants public health professionals legal capacity to implement mandatory isolation (of cases), quarantine (of contacts) and diagnostic investigation[44]. The full extent of the potential impact of SARS-CoV-2 in Europe was first demonstrated in northern Italy in February and March 2020, when the rapid spread of the virus led to the hospitalisation of thousands of patients, overwhelming hospital capacity[45]. During the same time period, many Dutch citizens travelled to Italian ski resorts as well as surrounding regions such as Austria and Switzerland; further expansion beyond the Italian epicentre was later demonstrated to have taken place earlier than initially thought[46]. The first notified case of COVID-19 in the Netherlands on 27 February 2020 had an epidemiological link to Lombardy[47]. However, a highly restrictive case definition (based on strict geographic and clinical criteria) was used at that time to allocate scarce tests. It is therefore possible that undetected importation of COVID-19 had already occurred. Between 27 February and 12 March 2020, attempts were made by regional public health services in the Netherlands to contain the spread of the virus through rigorous source and contact tracing. It quickly became apparent, however, that with a rapidly growing number of active cases, each with many contacts, sustaining this intensity of response was unfeasible with existing human resources. This realisation was confirmed by the emergence of cases without a travel history to a defined high-risk country or an epidemiological link to another known case, indicating widespread domestic transmission. The Dutch government therefore implemented a series of public health regulations from 12-15 March 2020 onwards to limit ongoing community transmission, reducing the incidence of severe COVID-19 and mitigating the impact on acute hospital care. These regulations included, for instance, travel restrictions, and the closure of non-essential stores, schools, universities, and other public services to minimise social contact[48]. By 1 June 2020, the National Institute for Public Health and the Environment (RIVM) had recorded 46,000 notified cases (disproportionately hospitalised individuals tested prior to or at admission) and almost 6,000 deaths due to COVID-19[49].

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