Our COVID-19 Cluster


With the approval and distribution of both Pfizer and Moderna’s COVID-19 vaccines hopefully ushering in “the beginning of the end” of the COVID-19 pandemic, we would like to reflect on one of the most significant challenges our hospital faced in 2020—a year full of trials and tribulations.

Last September, the Brigham identified a cluster of COVID-19 infections that ultimately affected 52 individuals on 3 units, including 38 employees and 14 patients. An infectious disease cluster is an “aggregation of cases grouped in place and time that are suspected to be greater than the number expected, even though the expected number may not be known.1” Meaning, based on the number of cases and a thorough investigation into their potential sources, it is likely that these cases were associated with one other, possibly being transmitted from employee-to-patient, patient-to-patient, or employee-to-employee.

As experts in patient safety whose priority it is to keep our patients and staff safe and healthy, our primary goal was to understand the cluster as quickly as possible and prevent it from growing.  At the same time, we recognized that this cluster could also serve as an opportunity for significant learning about the disease, that would not have been possible otherwise.  Famously, John Snow, considered by many to be “the Father of Epidemiology,” was able to use a cluster of cholera cases to become the first person to identify how this infectious disease was transmitted.2 (You can learn more about this discovery here.)

The investigation of our COVID-19 cluster revealed that the cluster began with a highly infectious, highly symptomatic patient who tested negative on arrival to the hospital, and then spread infection to several staff members and roommates before being diagnosed with COVID-19.  Factors that may have contributed to the further spread of the virus to other patients and staff included very high viral loads amongst infected individuals (making them more likely to spread their infection to others), patients rarely wearing their masks during encounters with staff, low rates of eye protection use by providers, and providers eating in small, enclosed spaces close together. The cluster ultimately ended through the use of an array of intensive interventions, including extensive contact tracing and repeated testing of all patients and staff on the impacted hospital floors.

Since identifying the contributing factors, we have worked to improve our practices and share our learnings broadly so those at our hospital and beyond can avoid a similar cluster in the future.  New measures implemented include increased testing of all inpatients (on arrival, again 72 hours after arrival, and every 3 days thereafter for patients receiving aerosol generating procedures); easy access to on-site testing for employees; a redoubling of efforts to improve staff compliance with eye protection and patient compliance with masking; and de-densification of staff work rooms and eating spaces.

By sharing our cluster experience and findings, we are demonstrating our unwavering commitment to transparency regarding patient safety events. Given the heightened concern and media attention on COVID-19 globally, we are proud that our team quickly disclosed the event to all potentially impacted patients and their families, our employees, as well as news organizations for public awareness.3 It is our hope that by sharing our story widely, other organizations will be able to learn from our experiences and that, in some small way, this event can contribute to the global fight against COVID-19.

To learn more, you can read about this work published in Annals of Internal Medicine here.


  1. Centers for Disease Control and Prevention. Principles of Epidemiology in Public Health Practice, Third Edition- An Introduction to Applied Epidemiology and Biostatistics. https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section11.html.
  2. Centers for Disease Control and Prevention. John Snow: A Legacy of Disease Detectives. https://blogs.cdc.gov/publichealthmatters/2017/03/a-legacy-of-disease-detectives/.
  3. New York Times. Coronavirus in the US.: Latest Map and Case Count.https://www.nytimes.com/interactive/2020/us/coronavirus-us-cases.html#clusters.