Dutch study does not find evidence of transmission of COVID-19 in hospitals

NIAID CEIRS | Research Publication Commentary

Sikkema RS et al. (2020) COVID-19 in health-care workers in three hospitals in the south of the Netherlands: a cross-sectional study. Lancet Infect Dis. S1473-3099(20)30527-2.

Researchers from the Center for Research on Influenza Pathogenesis (CRIP) recently published a study in The Lancet Infectious Diseases investigating COVID-19 infections in healthcare workers in the Netherlands. Previous studies of MERS-CoV found that nosocomial transmission (infections of a disease acquired in a hospital) accounted for 50% of new cases. Here, the authors investigated potential sources of infection of healthcare workers by combining epidemiologic data with whole genome sequencing data of SARS-CoV-2 from clinical samples.

Hospital personnel wearing appropriate PPE

This study was performed in three hospitals in the Netherlands in the weeks after the first COVID-19 case in the Netherlands was confirmed on February 27th, 2020. Researchers developed a cross-sectional study among the healthcare workers employed at the three hospitals. The study included healthcare workers who had COVID-19 compatible symptoms (fever or respiratory symptoms) up to 10 days prior to being tested for SARS-CoV-2 infection. Any healthcare workers who tested positive for SARS-CoV-2 were then interviewed for travel history, attendance at large gatherings, and other epidemiologic data. Clinical samples were also collected to perform whole genome sequencing of SARS-CoV-2.

The cross-sectional study screened 1,796 (15%) of the healthcare workers at the three hospitals for SARS-CoV-2 using RT-PCR. Of these tests, 96 workers tested positive (5.3%). Of these healthcare workers, only 32% had close contact with individuals with confirmed COVID-19 within 14 days prior to symptom onset. Only 3% had contact with a COVID-19 patient, while 19% reported close contact with a colleague who had confirmed COVID-19. Sixty-three percent of healthcare workers testing positive for COVID-19 reported attending a carnival that had recently taken place in February. From the epidemiological data, it appeared that the majority of hospital workers may have been infected via community spread. However, researchers then analyzed the SARS-CoV-2 sequences to see if any patterns of virus introduction could be identified. Genomes of SARS-CoV-2 viruses from 50 healthcare workers and 10 patients were analyzed and based on the genetic sequence similarity, the sequences were grouped into three clusters. Each cluster contained a mixture of healthcare worker and patient samples from each of the three hospitals. While sequence similarity was high in samples taken from healthcare workers and patients at the same hospital within each cluster, researchers did not identify any patterns consistent with transmission between healthcare workers and patients. Together with the epidemiological data, this suggests that infections in health care workers were community acquired.

This study was the first to use whole genome sequencing to investigate nosocomial transmission of SARS-CoV-2. While it does not appear that transmission between healthcare workers and patients was a significant source of infection in this study, it was early in the outbreak and genetic diversity was limited. The authors note that healthcare workers should continue to use recommended PPE and follow infection control protocols to prevent transmission within the hospital. Future studies using a greater number of samples and from later in the outbreak could provide more insight into whether nosocomial transmission is a source of healthcare worker infections.