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COVID-19 in health-care workers in three hospitals in the south of the Netherlands: a cross-sectional study

Our take —

This study describes COVID-19 screening of a large number of healthcare workers in three hospitals in the Netherlands, and how combining genomic and epidemiological data can be used to better understand transmission to and between healthcare workers. The genomic results clearly demonstrated that hospital outbreaks were not due to single introductions spread predominantly through subsequent nosocomial (hospital-based) transmissions, but rather point to multiple introductions into each hospital through community-acquired infections. However, limited sampling makes it difficult to determine the exact extent to which nosocomial transmission played a role in these hospitals.

Study design


Study population and setting

A total of 1,796 of 12,022 (15%) healthcare workers at three hospitals in the Netherlands were tested for SARS-CoV-2 between March 2 and March 12, 2020. To be eligible for testing, healthcare workers needed to report fever or mild respiratory symptoms in the 10 days prior to screening. Additionally, all patients testing positive for SARS-CoV-2 as well any admitted two days or more before the last symptom onset date of a healthcare worker in their respective hospital were included in the analytic dataset. Structured interviews were performed among those who tested positive to ascertain epidemiological data and movement and contact history, and whole genome sequencing was performed from swabs collected from positive patients. The goal of this study was to combine epidemiological and genomic data to understand sources and modes of transmission among healthcare workers and patients.

Summary of Main Findings

Among the 1,796 health-care workers and 865 patients tested for SARS-CoV-2 during this period, 96 healthcare workers (5%) and 23 patients tested positive (3%). The median age of positive cases among healthcare workers was 49 years (range: 22-66), and over 80% were female (n=80). Close to one-third (31/96) of healthcare workers reported a known contact with an individual with confirmed COVID-19 in the two weeks prior to onset of symptoms. The authors generated 50 SARS-CoV-2 sequences from the 96 positive healthcare workers and found that these sequences belonged to three major clusters. Each cluster contained identical or near-identical sequences from within the same hospital, and each hospital was associated with sequences belonging to multiple clusters. Low sample sizes make it difficult to identify specific nosocomial transmissions, though presence of multiple clusters in each hospital suggests multiple sources for each outbreak.

Study Strengths

The use of both epidemiological data and genetic sequencing data allows for more concrete and nuanced understanding of modes of transmission. Sequencing data from three different hospitals allows the authors to better understand genomic diversity circulating in the Netherlands.


Genomic sequences were only available for a limited number of healthcare workers and patients, and only symptomatic individuals were tested. This means that asymptomatic transmission may not be captured, or that transmission could occur between healthcare workers and patients whose genomes were not sequenced. Further, what constitutes a cluster is not clearly defined in the methods and results.

Value added

This study shows that COVID-19 cases in three Dutch hospitals were due to multiple introductions from elsewhere, arguing against widespread nosocomial transmission.

This review was posted on: 25 August 2020