This CDC investigation of COVID-19 cases in Chicago identified a cluster of 16 confirmed or probable cases, including three deaths, likely resulting from one introduction. Extended family gatherings including a funeral and a birthday party likely facilitated transmission of SARS-CoV-2 in this cluster. Findings support CDC recommendations to avoid gatherings.

Early reports of person-to-person transmission of SARS-CoV-2 have been among household contacts, health care workers, and within congregate living facilities. However, widespread community transmission, as is currently being observed in the United States, requires more expansive transmission events between nonhousehold contacts.

This report describes the cluster of 16 cases of confirmed or probable COVID-19, including three deaths, likely resulting from transmission of SARS-CoV-2 at two family gatherings (a funeral and a birthday party). Transmission mostly occurred between nonhousehold contacts.

The median interval from last contact with a patient with confirmed or probable COVID-19 to first symptom onset was 4 days. Within 3 weeks after mild respiratory symptoms were noted in the index patient, 15 other persons were likely infected with SARS-CoV-2, including three who died. The index patient was apparently able to transmit infection to 10 other persons, despite having no household contacts and experiencing only mild symptoms for which medical care was not sought.

These data illustrate the importance of social distancing for preventing SARS-CoV-2 transmission, even within families, and support current CDC social distancing recommendations intended to reduce SARS-CoV-2 transmission. U.S. residents should follow stay-at-home orders when required by state or local authorities.