Thousands of residents displaced by Hurricane Katrina four years ago are still living in government-issued trailers, federal data indicate.

The federal government has made it a priority to move the Mississippi and Louisiana residents from the temporary trailers, especially after formaldehyde and other toxins were found in them. This month, the Federal Emergency Management Agency and the U.S. Housing and Urban Development agency announced programs to help relocate residents from the trailers, including $50 million in housing vouchers, USA Today reported.

The numbers in Mississippi and Louisiana -- 781 families and 2,100 families, respectively -- and are down considerably from the 134,000 temporary trailers and mobile homes sent to the Gulf Coast immediately after Katrina devastated the area in August 2005. Some families are living in the trailers because of hurricanes Gustav and Ike, which struck Louisiana last summer.

Chrystal Utley of the Mississippi Center for Justice, which advises disaster victims, said slow-moving federal housing funds, elderly and disabled residents unable to navigate the system, a lack of affordable rental units and rising insurance rates combined to keep the trailers from being vacated completely, USA Today said.

"We're dealing with the hard-to-house people," Utley said.