Signage at the Bass Park coronavirus testing site in Bangor.

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A single salesperson caused a “cluster” of cases early on in the new coronavirus outbreak in Maine and may have infected people in other states, a top public health official said Thursday.

Maine Center for Disease Control and Prevention Director Nirav Shah said a “fair number” of the cases in the state were traced to an individual who “seemed to have had a pattern of spreading COVID-19 across a number of states” and infected several others in Maine after having a series of meetings at one location.

[Our COVID-19 tracker contains the most recent information on Maine cases by county]

The discovery highlights how the spread of the coronavirus can often be traced back to individual people and individual gatherings in which infected people spread the highly contagious virus. It’s also an example of the work the state’s public health agency has been doing to track down sources of infection and identify how the coronavirus has spread.

The traveling salesperson’s situation is one of the first known instances in Maine in which one sick person caused several other people to become sick through a single point of contact. A number of other coronavirus outbreaks in the U.S. have been traced back to individual gatherings such as parties and funerals where infected people spread the virus.

A study of the new coronavirus outbreak in the U.S. Centers for Disease Control and Prevention’s Emerging Infectious Diseases journal says tracking and preventing these events — which fueled the 2003 SARS and 2012 MERS outbreaks — is critical to slowing the virus’ spread.

Those events in the U.S. have included a Connecticut party attended by a South African businessman that is believed to have caused an outbreak in the town of Westport. The U.S. CDC found a cluster of up to 16 confirmed cases and three deaths in Chicago that likely stemmed from one individual who attended a funeral and a birthday party. Two funerals in rural Georgia are linked to at least 20 people getting sick. And in Massachusetts, a majority of the state’s early coronavirus cases were connected to a late February employee meeting of the biotechnology company Biogen.

[17 nonresidents have tested positive for the coronavirus in Maine]

Shah did not say what industry the person worked in or the person’s age, gender or state of residence, citing privacy reasons. While the salesperson may not be “patient zero,” he said discovering the case allowed the CDC to track the virus “pretty far” based on the person’s travel.

Shah noted there can be a delay between when people start to feel symptoms of the virus and when they get tested. People can also spread the virus before they experience any symptoms. Those delays can mean it can take almost three weeks for the CDC to record a case. The state’s epidemiologists then have to interview the infected people to get a sense of where they have been and with whom they may have been in contact, a process called contact tracing.

That information can lead to the identification of other potential coronavirus cases, letting people know that they might have contracted the virus after contact with someone who was infected and that they should take measures such as isolating themselves to prevent further spread.

Maine’s first confirmed case of the new coronavirus was recorded in Androscoggin County, but the outbreak quickly moved to neighboring Cumberland County.

That county, Maine’s most populous, is home to almost half of the state’s 560 confirmed cases. It’s one of two counties where the CDC has confirmed community transmission — when it becomes nearly impossible to pinpoint sources of infection. The other county is York County, which has the second-highest number of cases in the state.

The majority of the 560 confirmed cases of the virus are believed to have transmitted within households, not within the general public. Shah said Thursday that 43 of the state’s cases have occurred in congregate settings — locations such as retirement communities, group homes and homeless shelters.

Watch: Nirav Shah on whether you should use fabric masks

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