U.S. health officials have identified 5,000 fatalities in New York City between March and early May that may have been caused by Covid-19 but weren’t counted as part of the official coronavirus death toll, the Centers for Disease Control and Prevention said Monday.

New York City health officials reported 18,879 total Covid-19 deaths between March 11 and May 2, — 13,831 of which were confirmed by a lab and 5,048 of which were categorized as probable cases based on the patients’ symptoms and other factors, according to a new CDC report.

There were an additional 5,293 deaths that weren’t previously identified as confirmed or probable coronavirus cases that “might have been directly or indirectly attributable to the pandemic,” the CDC said.

The number of confirmed or probable Covid-19 deaths might not include deaths among people with the virus “who did not access diagnostic testing, tested falsely negative, or became infected after testing negative, died outside of a health care setting, or for whom Covid-19 was not suspected by a health care provider as a cause of death,” the CDC wrote.

In addition, social distancing practices, the demand on hospitals and health-care providers, and public fear related to Covid-19 might lead to delays in seeking or obtaining lifesaving care, the agency said.

New York City is the epicenter of the outbreak in the United States. Since the city reported its first case on March 1, health officials have confirmed more than 184,000 cases and at least 19,789 deaths, according to data compiled by Johns Hopkins University. U.S. health officials have suggested the true number of cases and deaths is likely much higher as some people infected with the virus go undetected.