NEW YORK, Oct. 17 (Xinhua) -- Chicago takes the top spot again, trailed by Los Angeles, New York, Washington, D.C. and San Francisco, according to the Top 50 Rattiest Cities list recently issued by Orkin, the primary provider of pest control services in the United States.

"Rats have taken to the streets of Chicago ... And for the sixth consecutive time, the Windy City takes the top spot," said a release posted on the website of Orkin.

"New to the Top 10 this year is Baltimore, taking the eighth spot, and moving into the Top 20 is San Diego, rising 13 spots to secure the #19 ranking," it added.

In an unprecedented year, the visibility of rodents has increased, creating concern for homeowners and business owners alike. As reported in the spring, the pandemic-driven closure of restaurants forced rodents to find new food sources, said the release.

"Without food waste to consume, these pests were seen scavenging new areas and exhibiting unusual or aggressive behavior," it said.

The presence of rodents became so relevant that the Centers for Disease Control and Prevention issued rodent control guidance on ways to keep rats and mice out of homes and businesses, said the release.

"As we approach colder months, rodent activity will only continue increasing as these pests seek shelter in warm areas with available food and water. As the U.S. population spends more time at home this season, residents should pay extra attention to the attractants that entice rats and mice," it added.

Orkin ranked metro regions by the number of new rodent treatments performed from September 1, 2019 to August 31, 2020. This ranking includes both residential and commercial treatments.