(Undated)  --  Portland is ranked 50th on this year's list of the top 50 U.S. cities for bed-bug infestations.  The data gathered by Orkin Pest Control is based on the most treatments the company provided in a one-year period that ended November 30th.  An Orkin pest-control expert says more people are affected by bed bugs than ever because the critters travel so easily from place to place.  Baltimore leads the list of cities for bed-bug infestations, followed by Washington, DC; Chicago; New York; and Columbus, Ohio.  The Seattle-Tacoma area is in 34th place.