Masks in boxes sit on a table at Boomers Stadium parking lot in Schaumburg, Illinois, May 6, 2020. (Photo: AP)

Medical examiners in Chicago are planning to probe deaths involving heart attacks and pneumonia for evidence of COVID-19 as far back as November, reported CNN citing Cook County spokesperson Natalia Derevyanny.

Chicago reported its first known death on March 16.

"The goal is to see if this virus was present before we knew of it," Derevyanny said.

Viral pneumonia cases along with heart attacks caused by arteries being blocked will be examined, according to the report.

It came as a mayor of a U.S. city in the state of New Jersey claimed he recently tested positive for COVID-19 antibodies and believes he was infected by the virus in November, about two months before the first confirmed case in the country.