(Reuters) – Health officials in the U.S. state of Illinois’ Cook County, which includes the city of Chicago, will probe deaths involving heart attacks and pneumonia for indications of COVID-19 as far back as November, a county spokeswoman said on Wednesday.

Chicago recorded its first death from the coronavirus on March 16 but the medical examiner’s office from Cook County is planning to review case records from earlier deaths for COVID-19 signs, Cook County spokeswoman Natalia Derevyanny told Reuters in an emailed statement.

“The Medical Examiner’s Office will review pneumonia and heart attack deaths that fell under our jurisdiction as of November 2019”, the spokeswoman said.

“While we have not seen specific indications of COVID-19 deaths in Cook County before mid-March, we want to ensure that we have a full picture of when this virus entered our community and its true impact”.

Health officials have said that the novel coronavirus circulated in the United States weeks earlier than thought and was mistaken for flu.

The virus emerged in California in January and a 57-year-old woman died of COVID-19 on Feb. 6, far earlier than any other reported cases in the United States.

It was previously thought that the first U.S. death from COVID-19 was in Washington state on Feb. 29.

The coronavirus has infected about 1.2 million people in the United States and caused about 71,000 deaths, as of late Tuesday.

The global death toll from the outbreak stands at over 255,000 with more than 3.6 million infections.

(Reporting by Kanishka Singh in Bengaluru; editing by Nick Macfie)