GALLUP, N.M. — A surge in H.I.V. infections on the Navajo reservation here has doctors and public health workers increasingly alarmed that the virus that causes AIDS has resurfaced with renewed intensity in this impoverished region.

A report released last month by the federal Indian Health Service found that there were 47 new diagnoses of human immunodeficiency virus on the reservation in 2012, up 20 percent from 2011. Since 1999, new H.I.V. cases among Navajo are up nearly fivefold, the report found. The tally of new cases from last year represents the highest annual number recorded among the tribe by the health agency.

“I’m scared to death,” said Dr. Jonathan Iralu, an infectious disease specialist who runs an H.I.V. clinic in this dusty town where old trading posts and ramshackle motels line the main drag on the edge of Navajo land, not far from the Arizona border. “The numbers show there is a dangerous rise, and the time to act is now, before it’s too late.”

Dr. Iralu, who compiled the report, remembers hearing the stories from former colleagues about the late 1980s when AIDS first struck the reservation. Navajo men would walk into the Indian Medical Center in Gallup sick with a fever or a cough, and a few days later they would be dead.