The Bucks County Department of Health said Saturday that 12 recent cases were traced to a New Jersey resident who attended "multiple" house gatherings at the shore.
The exposures occurred at a gathering of college-age students over the holiday weekend in Cape May County, according to the New Jersey Department of Health. The department has not identified any additional cases at this time.
In 11 of the cases, Bucks County residents had attended the same gatherings as the New Jersey resident, and a 12th case was via family spread in Bucks County, the local health department said. The links were discovered through "thorough contact tracing," spokesman Larry R. King said.
King said the Bucks County health department requires people who are in the same household or have had steady contact with someone who has a confirmed case of COVID-19 to quarantine and get tested.
More infections are likely among family members of these new cases, Dr. David Damsker, director of the Bucks County Health Department, said.
"This is exactly why we can't let our guard down now, even if it feels 'safe' to be at the beach," Damsker said in a statement. "One unlucky exposure can lead to a large cascade of cases down the line. We want everyone to enjoy the warmer weather and have fun, but let's keep in mind that COVID is still circulating in the community at baseline levels."
The New Jersey health department said it also is investigating the exposure and conducting contact tracing to identify additional illnesses, although it noted that now is the outer limit of the virus' 14-day incubation period.
"We are gathering information to understand who was [the] initial source of exposure that caused the outbreak," New Jersey State Epidemiologist Dr. Tina Tan said in a statement.
Damsker urged residents to wear face coverings when they attend gatherings with people outside their household and to take precautions in public as Pennsylvania continues to reopen. On Friday, Bucks County moved to the "yellow phase" of Gov. Tom Wolf's reopening plan, allowing for gatherings of up to 25 and outdoor dining, in-person retail, child care and businesses with in-person operations to resume.
Nearly 5,000 Bucks County residents have tested positive for COVID-19, based on figures from the local health department. Pennsylvania has had 73,827 confirmed cases and 5,953 deaths, according to the state health department.
New Jersey has had 164,497 confirmed COVID-19 cases and 12,214 deaths, based on figures from its state health department.