Simply put you bring them home with you. If you live in an apartment the colonies unchecked may expand into your suite but the primary source of bed bugs is them getting into your luggage and bringing them home.
It is not an issue of being dirty or having a messy house, pure and simple they come after you to suck on your blood. Their food source is blood.
There is an absolute global epidemic of bed bugs and the more you travel the greater the chance you will encounter them in hotels, independent of the number of stars the hotel has.
Bed bugs are incredibly insidious. They are master hiders and being nocturnal come out from their hiding place at night to feed. They do like be close to their food source and the first colony may reside in the mattress, box spring or in the headboard.
Before you book a hotel read the reviews and look for the mention of bed bugs.
When you arrive in your hotel room pull back the covers and sheets look for pepper spray fecal matter, blood smears and bed bug casings. If you see anything suspicious get another room. It is not unheard of to get a hundred bites in one night.
Do not leave your bed clothing on the bed or put your suitcases on the bed. Use bed bug luggage liners. When you arrive home do not put your suitcases in your bedroom instead wash all your clothing and leave the bed bugs in the garage or your storeroom.
If you are getting bitten and think you have bed bugs, do not delay get a specially trained bed bug dog to inspect your home and if you find them discuss your alternatives with a pest control expert.
Picture by cuttlefish