More people in the United States are affected by bed bugs now than ever before, with Baltimore coming in at number one in a pest control company’s list of U.S. states with the worst infestations.

The Top 50 Bed Bug Cities list, annually released for six years now by Atlanta-based pest control services and protection company Orkin, is based on treatment data from the metro areas where the company performed the most residential and commercial bed bug treatments from December 1, 2015 to November 30, 2016.

Baltimore moved up nine spots since the previous year, trailed by Washington, D.C., Chicago, New York, Columbus in Ohio, Los Angeles, and Detroit. Chicago, which topped the list for four straight years, dropped down to number three this year, while four metro regions – namely Las Vegas, Portland, Salt Lake City, and Greensboro-High Point-Winston Salem – made it to the list for the first time.

The bad news: bed bugs, which were “virtually unheard of” in the country a decade ago, are a growing problem.

“People may have bed bugs and not know it, because many people have no physical reaction to bed bug bites. That’s why it’s important for people everywhere to inspect for bed bugs regularly,” said Ron Harrison, Ph.D., entomologist and technical services director at Orkin.

The higher figures could also mean the education part has caught up with bed bugs growth, observed Orkin’s Midwest Division technical services manager John Kane, who revealed a 10 percent climb across the country as a whole.

Bed bugs are making a grand comeback since the late 1990s, according to Orkin. The National Pest Management Association’s Bugs without Borders Survey in 2015 showed that a whopping 99.6 percent of pest control professionals around the U.S. have treated bed bugs in the last year.

A recent study found that bed bugs nowadays are even harder to kill as they have developed thicker skin to resist common insecticides.

But contrary to popular belief, bed bugs are not a symptom of uncleanliness. Harrison warned that anyone can get them in their home – from mansions to public housing – as the bugs travel with great ease and only demand blood to survive and travel.

While they can be detected anywhere from homes to public facilities, bed bugs are rather difficult to detect and treat due to their tiny size (around the size of an apple seed) and ability to live up to one year without feeding. Often the first sign of an infestation are the bugs themselves, as well as small and dark stains they leave behind.

Here are some ways to prevent and control a bed bug infestation at home:

1. Regularly inspect all areas of the house, such as mattress seams and those convenient spots behind headboards and electrical outlets.
2. Reduce clutter.
3. Before they enter your home, inspect all secondhand furniture.
4. Dry likely infested beddings, curtains and stuffed toys on the hottest temperature possible.
5. When traveling, remember S.L.E.E.P.: Survey the hotel room; lift and look in potential hiding spots; elevate luggage away from bed and wall; examine your stuff while repacking; and place all dryer-safe clothes you’ve unpacked in the dryer in the highest setting for a minimum of 15 minutes.