Health officials say the rodents have gone so far as cannibalism and eating their young after food sources such as restaurants that they rely upon shutdown.
"Some jurisdictions have reported an increase in rodent activity as rodents search for new sources of food. Environmental health and rodent control programs may see an increase in service requests related to rodents and reports of unusual or aggressive rodent behavior," the CDC wrote.
Residents and businesses are urged to take preventive measures to eliminate conditions that may attract and support rodent presence.
Those actions include sealing up access into buildings, removing debris and heavy vegetation, keeping garbage in tightly covered bins, and removing pet and bird food from their yards.
The CDC provides more information and guidelines on its website.
New York City Mayor Bill de Blasio's office said at the end of April that the city was resuming exterior-only inspections in areas with high number of complaints of rat activity.
Rat problems can be reported in New York City by calling 311. There's also more information available on the NYC Health website.
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