(AP)—Federal investigators probing the hantavirus outbreak blamed for three deaths at Yosemite National Park recommend that design changes to tent cabins and other lodging run by private concessionaires first be reviewed by National Park Service officials.

The report released Monday by the Interior Department's Office of Inspector General found that park officials responded to the outbreak appropriately and within department policy.

But that policy did not require park officials to approve design changes made to the "Signature tent cabins" by concessionaire Delaware North Companies Parks and Resorts, which had added rafters and wall studs to the structures.

Investigators determined that , which can carry the illness, nested inside the double walls of the new tents.

At least eight of the nine tourists who fell ill stayed in the cabins.