CARLSBAD -- County health officials launched an investigation Thursday into reports of five to seven cases of aplastic anemia, a rare bone marrow disorder that occurs in about one in every 1 million people in the United States.

The investigation will center first on establishing the number of cases of the disease through interviews with parents, said senior epidemiologist Jeffrey Johnson of San Diego County Public Health Services. Johnson said a call from a concerned North County parent Wednesday prompted the investigation.

Doctors at Rady Children's Hospital in San Diego are treating five people with the disease from across the county, including cases in San Marcos, North Vista, Encinitas and El Cajon, hospital spokesman Tom Hanscomb said Thursday. Hanscomb said Children's Hospital officials reported the names of two people diagnosed with aplastic anemia to county health officials.

Dawn Norby, the mother of a 9-year-old son diagnosed with the disease in December by a Rady Children's Hospital doctor, said county health officials interviewed her Friday.

Johnson said the county is working with doctors at the hospital in the investigation.

Aplastic anemia is not contagious, according to a variety of health experts.

Between 300 and 400 cases of the blood disorder are diagnosed each year across the nation, according to Cecelia Petro, a researcher with the Aplastic Anemia and MDS Foundation in Annapolis, Md.

Marilyn Baker, former director of the foundation, said the disease significantly reduces the number of blood cells manufactured in the body's bones, leaving sufferers tired, prone to extreme bruising and open to secondary infections.

"It's when the stem cells in bone marrow stop producing enough of the three blood cells -- red, white and platelets," Baker said. Each case is different, with varying counts of each type of cell, she said.

Aplastic anemia is not considered a cancer because it does not grow atypical cells.

The disease is contracted in four basic ways -- exposure to toxic chemicals such as benzene, exposure to radiation, exposure to various viruses such as Epstein-Barr and hepatitis, and some drugs used in treating epilepsy -- according to Baker, whose organization serves as a national clearinghouse for information and education on the disease.

In many cases, the cause is hard to define, Baker said.

Extreme and unusual bruising is one of the key symptoms of aplastic anemia, Baker said. Extreme fatigue, extended bleeding and slow recovery from illness are also common. Baker said a simple blood test can suggest the existence of aplastic anemia, and a bone marrow biopsy can confirm it.

A bone marrow transplant is the only cure for the disease, Baker said. However, the disease can be treated with a few drug regimens that have improved over the 17 years she has served the foundation, Baker said. Between 60 percent and 85 percent of patients respond well to the drugs.

Aplastic anemia is not on the list of reportable diseases to county, state and national health officials, Johnson said.

Calls to the National Institutes of Health and the Centers for Disease Control and Prevention in Atlanta were not retuned as of press time Friday.

Local cases

Four North County parents who live within seven miles of each other confirmed Thursday and Friday that their children have been diagnosed with aplastic anemia -- three since November.

"This is an unusual occurrence of such a number in a geographical area and time frame," said Baker.

Dawn Norby said Trevor, her 9-year-old son, first showed symptoms in November when the boy "barely bumped into the wall" coming down the stairs of their home in the Carlsbad neighborhood of Rancho Carrillo. The next day Trevor, a student at Carrillo Elementary School in San Marcos, had a 4-inch-wide bruise "that protruded from his skin 2 inches," Norby said.

Trevor's blood cell counts are rising after receiving a drug treatment that suppresses the immune system at Children's Hospital, according to his mother. The treatments shock the body into manufacturing more blood cells, she said.

Trevor, an avid baseball fan, idolizes San Diego Padres pitcher Trevor Hoffman. Norby said her son has a lot of energy and bounces on the family trampoline "about 500 times a day" as he waits for clearance to play ball again. A pitcher himself, Trevor told his mom he wants to get back on the mound to give Hoffman a run for his money.

Soon-Gill Schnellinger's 6-year-old daughter, Renee, in Vista was diagnosed with aplastic anemia in December. The kindergartner at Lake Elementary School in Vista Unified School District suffered from bruising, pale yellow skin and a condition called petechiae, characterized by pinpoint bleeding under the skin and in the eyes.

She has been getting blood transfusions from her brother, and her blood cell counts are rising, said Schnellinger.

"We're not out of woods yet," Schnellinger said. "But she's doing well and was cleared to go back to school today."

Kennedy Kraus, a second-grader at Mission Estancia Elementary School in south Carlsbad, was diagnosed with the disease in November. The family could not be reached for comment Friday, but recently told the North County Times that Kennedy may need a bone marrow transplant. The school's PTA hosted a bone marrow drive on Feb. 14 to help identify potential donors. Kennedy is being treated at City of Hope, a research and treatment center in Los Angeles.

Sherri Gilmour said her son, Hunter, a 17-year-old student at La Costa Canyon High School, was diagnosed with aplastic anemia more than three years ago. Hunter was treated with the immune system-depressing drugs at City of Hope but his body did not respond well, Gilmour said. Gilmour said her son nearly died when his kidneys failed as a result of the drug treatments and blood transfusions. He received a bone marrow transplant seven months ago, and now most of his blood cell counts are within normal ranges, Gilmour said Friday.

Hunter has just returned to school and just earned his driver's license, she said. Gilmour said she is writing a book about the experience.

Contact staff writer Philip K. Ireland at (760) 901-4043 or pireland@nctimes.com.