Infections first emerged in the Hubei province of China. SARS-CoV-2 was first identified in the context of a super-spreading event in the Huanan Seafood Market in the city of Wuhan.
A UMass student returned from his home in Wuhan, China, with the virus. No other infections resulted. Officials retraced the student’s steps and disinfected every railing and doorknob he may have touched.
A recent traveler to Italy and Switzerland carried the virus, and a fellow passenger was the third case, but these strains were also successfully isolated.
Cases began to arrive at the Berkshire Medical Center, and soon totaled more than 500. Many had attended the same sporting event. The source was most likely a strain spreading along the West Coast of North America—a sign of widespread and uncontrolled transmission.
An international business conference gathered 175 executives in Boston. The infection most likely came from Europe. By March 11, 77 of the 96 cases in the state were tied to the Biogen conference—the state’s first super-spreading event.
Two strains at the Biogen conference spread widely: G26233T and C2416T. G26233T was exported to several states as well as Australia, Sweden and Slovakia. C2416T has traveled internationally and accounted for 2.7% of U.S. sequenced lineages through May.
Cases were detected at two Boston homeless shelters, Pine Street Inn and Southampton Street Shelter. Of 193 SARS-CoV-2 genomes, 105 were of lineages associated with the Biogen conference.
The virus was found in 85% of residents and 37% of staff at one institution. Most cases came from a single, recent source, though the history of that source remains unknown. Viruses were then exported to Utah and California.
By the second week of April, SARS-CoV-2 was disproportionately hitting dense, low-income areas. Chelsea become the local epicenter by April 9, with an infection rate almost four times that of the statewide average. The source of most infections is unknown.