Bed bugs are wingless, nocturnal creatures that need a blood meal to reproduce. They have two mouth parts, one injects an anesthetic, the other sucks blood. They have 5 life stages and can live for more than a year between feedings. These parasites can reproduce quickly and will then go in search of new food sources by hitch hiking onto luggage, furniture, clothing, etc.
They are quite small (about ½ the size of an apple seed), are experts at hiding and therefore are transported very easily by unsuspecting humans. If you want to get more information about bed bugs like how to kill Bed Bugs in the mattress, how to kill them etc then you can check the internet.
They are not associated with socio-economic levels, they are not an indication of hygiene or cleanliness, and they are not discriminatory. They could have entered any number of ways.
The reason for this unfortunate resurgence is Pesticide Resistance. Prevention took a new meaning – carefully examine everything that you bring into your home – including yourself! Individual bugs can be killed by squashing them. If you are not sure about what you are bringing in, place it in a large trash bags, spray or mist bed bug killer into the bag and seal tightly for 2-4 days.