LAKE ELSINORE - More than a year after Nicole Hedberg's unexplained death at age 25, her family's search for answers has turned toward a single-celled organism that lives in warm lake water and is blamed in the deaths of six people across the country this year.

No scientific evidence links Hedberg's death to the amoeba Naegleria fowleri, though the six recent Naelgleria deaths and media inquiries are prompting Riverside County officials to seek a conclusive answer. The amoeba lives naturally in organic sediment at the bottom of warm lakes but is occasionally deadly when inhaled.

Family members said Hedberg and her fiance, John Throesch, had recently moved into the second floor of a house on the shore of the lake, where they often swam and used their WaveRunner.

Throesch found Hedberg collapsed in her bedroom one afternoon in June 2006. He took her to a nearby hospital, where she regained consciousness, but soon went into seizures and then into a coma. Swelling eventually crushed her brain stem, and she died about 10 days later.

Considering her weakened and comatose state, doctors decided against drawing spinal fluid, which might have identified a microbe as the cause of her death. An autopsy ruled out bacterial meningitis, an early suspect, but was ultimately inconclusive as to what killed her.

A news article about the amoeba last week caught the attention of Dawn Loew, Hedberg's sister. To Loew and other family members who read the article, Hedberg's symptoms in the days before her death were remarkably similar to those of six young people who died this year after contracting Naegleria.

"The time lag, the symptoms, everything was just dead on," Loew said.

Amoeba are one-celled organisms that feed by surrounding and absorbing other microscopic organisms. Naegleria enters the human body in rare cases where organic sediment is stirred up, inhaled, and then somehow comes into contact with the olfactory nerve, which controls the sense of smell, according to the national Centers for Disease Control and Prevention.

As the amoeba feeds off nerve tissue, the host experiences a stiff neck, headaches and fever, symptoms that Loew said are consistent with what her sister reported. The colony eventually spreads to the brain.

Recent media attention is prompting the Riverside County coroner's office to resume research into the cause of Hedberg's death, said Jerry Franchville, a spokesman for the office. Franchville declined to discuss specific tests, but said that they would not include lake water.

"There's no evidence showing that her death is linked to the lake water," Franchville added. "The family just says it might have happened like that."

Since 1995, only a few dozen humans are known to have died after exposure to it, fewer than from lightning strikes or shark bites. For that reason, and because it requires a special test, physicians and coroners don't routinely check for it.

Most recently, Arizona resident Aaron Evans, 14, died last month after swimming in Lake Havasu, a reservoir on the Colorado River between California and Arizona. Other deaths have recently been reported in Texas and Florida.

Lake Elsinore isn't known to harbor Naegleria. Barbara Cole, director of disease control for Riverside County, said she doesn't see any cause for immediate concern.

Loew said her family is asking the Riverside County coroner's office to release tissue samples for testing. A spokesman for the department cited privacy concerns in declining to say whether the office still has any such samples. And because Hedberg was cremated, it isn't clear that any viable samples remain.

The coroner retains tissue samples for a minimum of 13 months, Franchville said. In some unresolved cases, the office retains samples for decades, though Hedberg's doesn't appear to be such a case, Franchville said.

Researchers at the CDC have offered to help California health officials with tests on any remaining samples, according to Loew.

Loew said Hedberg and Throesch met in Redondo Beach but had lived in Lake Elsinore for several months before her death. Throesch, who is now 30, attended Temescal Canyon High School and still had relatives in the area. He returned to Redondo Beach after Hedberg's death.

Contact staff writer Chris Bagley at (951) 676-4315, Ext. 2615, or cbagley@californian.com.