I didn't know. Not every hostel has bedbugs (although many in Saigon, if not most). When I arrive at a new hostel, I check if there are traces of bedbugs and, at night 1, I check what's happening around me on the bed with a phone torch around 2-3 am. So... The main drama happened because I kept my backpack in another part of the room, where, as it turned out, there was a townlet of bedbugs. :D
Bedbugs is a separate large topic, I can say much about it... Maybe, I should write a post about it.
RE: Cost of Budget Traveling in Ho Chi Minh City, Vietnam. $5 for Hostel, $2 for Dinner, $0.5 for Beer