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Unravelling the modes of transmission of SARS-CoV-2 during a nursing home outbreak: looking beyond the church super-spread event

Our take —

In March 2020, there was an outbreak of SARS-CoV-2 at a nursing home in the Netherlands. Despite an elevated secondary attack rate among church attendees and the timing of the outbreak following a church service, detailed epidemiologic investigation and whole genome sequencing revealed that the outbreak was likely due to many different, complex introductions into the community, including but not limited to a church service. Sequencing of positive samples can be a helpful tool for understanding the sources of transmission, and insights gained from these studies can be used to create an evidence-based prevention strategy for future outbreaks.

Study design

Case Series

Study population and setting

In early March 2020, an outbreak of SARS-CoV-2 was detected at a nursing home in the Netherlands. This outbreak occurred following an on-site church service. The goal of this study was to retrospectively create chains of transmission resulting from this outbreak and to evaluate the role of the church service in onward transmission. Symptomatic residents and healthcare workers of the nursing home as of March 14, 2020 were tested for SARS-CoV-2, and those testing positive prior to April 15 were included in these analyses. Non-residents who attended the church service were asked to complete a questionnaire. Contact tracing data were made available from the public health service (date of symptom onset, testing date, church attendance etc.) and mitigation measures and a map of the facility were provided by the nursing home. Whole genome sequencing was conducted on positive SARS-CoV-2 samples and compared with samples from the same area.

Summary of Main Findings

A total of 39 people attended on-site church service on March 8, 2020, including 13 residents and 26 non-residents. 77% (30/39) developed symptoms following the service, and 14/39 tested positive for SARS-CoV-2 (36%). Those attending the service were together for approximately 70 minutes (50-minute service with singing and eating and 20-minute coffee). Between March 8 and April 15, 21% (62/300) of residents and 5% (30/640) of healthcare workers tested positive for SARS-CoV-2. Among those residents who tested positive, 34% died (21/62). Among residents, the attack rate for churchgoers was 85% (11/13) and for non-churchgoers was 18% (51/287). Sequencing revealed that 7 of the churchgoers were infected with distinct viruses and that there were at least 17 different introductions of SARS-CoV-2 in the nursing home, suggesting that the outbreak was more complex than simply a seeding caused by the church event.

Study Strengths

Because the samples were sequenced and detailed comparisons made to samples in the same area, it was possible to determine that the church event was not the only source of the observed outbreak.

Limitations

Limited data were provided on the characteristics of the resident churchgoers and the resident non churchgoers. These data would have been helpful in understanding why resident churchgoers experienced a higher attack rate than resident non-churchgoers.

Value added

This study provides further evidence that complex, evidence-based mitigation strategies are needed to combat outbreaks for SARS-CoV-2. In this case, eliminating the church service alone would not have been enough to prevent an outbreak as transmission within the nursing during this time was already widespread.

This review was posted on: 19 December 2020