Large Gatherings, Workplace Spread Contributed to Thousand-Fold Increase in COVID-19 Cases

Over a three-week period from late February to early March the number of COVID-19 cases in the United States increased more than one thousand-fold, according to a new report from CDC. Several factors contributed to the rapid spread, including large gatherings in multiple states, travel- and workplace-associated infections, and unrecognized or “cryptic” transmission.

In February, when the number of confirmed COVID-19 cases in the U.S. was low, no restrictions on domestic travel or limitations on the size of gatherings were implemented. Three large events were held during the last week of February: the Mardi Gras celebration in Louisiana, with 1 million participants; an international professional conference in Boston, with 175 attendees; and a funeral in Albany, Georgia, with more than 100 attendees. Three weeks after these events, the number of confirmed cases in Louisiana, Boston, and Georgia spiked, CDC data show. Georgia’s Dougherty County, where Albany is located, had a cumulative incidence of 1,630 cases per 100,000 people, one of the highest in the country.

Workplaces that facilitated virus spread included nursing and long-term care facilities, hospitals, and meat packing facilities. In late February at a hospital in Solano County, California, 121 healthcare workers were exposed to a single patient with unrecognized COVID-19. Of the exposed workers, 43 became symptomatic and three tested positive for SARS-CoV-2, the virus that causes COVID-19. A separate CDC report found that 4,913 workers in meat and poultry processing facilities contracted COVID-19 during the period from April 9 to April 27.

Recognition of COVID-19 cases in the U.S. was complicated by the fact that the disease was introduced during influenza season and spread by people who had no symptoms.

“Preliminary results from serologic surveys suggest that even in the U.S. regions with the largest numbers of recognized cases, most persons have not been infected and remain susceptible,” the report concludes. “Therefore, sustained and concerted efforts will be needed to prevent future spread of SARS-CoV-2 within the United States.”