The state prosecution service in Munich said it had launched an investigation into an American who may have caused the surge in cases.
"There is an investigation for possible assault through negligence," said Andrea Meyer, from the state prosecutor's office.
The unnamed person, who had recently returned to Bavaria following a holiday abroad, chose to socialize despite having Covid-19 symptoms, according to Stephan Scharf, press officer at Garmisch-Partenkirchen District Administrator's Office.
Sharf said the individual took a coronavirus test and was told to stay indoors until they received their results, but did not do so.
The person subsequently tested positive and is now in quarantine, Scharf said. It's unclear which countries they may have visited, but the district administrator's office says it was not the US.
Sharp jump in cases
The individual works at Edelweiss Lodge, a US Armed Forces Recreation Center Resort in Garmisch-Partenkirchen, operated by the US Army and frequented by military personnel, Scharf said.
In the wake of the incident, 24 people at the lodge tested positive for coronavirus, and Garmisch-Partenkirchen has recorded a sharp jump in cases, with 33 reported on September 11 alone.
"We did not have so many even during the height of corona," Scharf said Saturday. "This kind of behavior of course is everything but commendable."
The town has drastically increased its pandemic measures following the outbreak.
"We have massively increased the testing station, now we have to wait for the test results," Scharf told CNN on Monday. "We don't know how many people the assumed spreader infected, although we know [the person] was out being infectious."
New regulations imposed in the town over the weekend mean local bars will now close at 10 pm. Parties are limited to 100 people -- down from 200 -- and groups eating indoors are capped at five, down from twice that number. Groups of ten are allowed to eat at a table outdoors, down from 20 previously.
Officials have calculated that the Bavarian town currently has a seven-day Covid-19 incidence rate of 55 cases per 100,000 inhabitants.
The town has a population of just 88,424, but its calculated incidence rate is high enough that it meets the German threshold of 50 cases per 100,000 inhabitants, which is the number needed to reimpose pandemic measures.
Lodge temporarily closed
The Edelweiss lodge has closed for two weeks following the outbreak, the US Army said.
"Several staff members of the Edelweiss Lodge and Resort here have tested positive for Covid-19," a US Army Europe spokesperson said in an emailed statement to CNN on Sunday.
"As a precaution, additional staff members who had prolonged, direct contact with the positive staff members have also been quarantined."
"The facility is working with US Army medical professionals and local medical officials to assess the situation and conduct contact tracing," the statement added.
"Due to the number of staff members affected, the decision has been made to close the resort for two weeks beginning Monday, September 14."
The staff member at the center of the incident has not spoken publicly.
In its statement, the US Army does not refer to the single individual in question. CNN is reaching out to the army for further clarification about the person and whether they face any disciplinary action.
Bavaria's Prime Minister, Markus Soeder, warned that coronavirus numbers were rising across the state on Monday.
WIthout referring specifically to the case of the US citizen, Soeder said local authorities should investigate whether they should fine people "high amounts" for such behavior.
"Garmisch-Partenkirchen is an example in irrationality," he told reporters at a press conference in Munich. "This carelessness also has to have consequences."
Germany has reported more than 262,500 cases of coronavirus overall, according to Johns Hopkins University.