Dr. Harry Gibbons is on the trail of a 125-year medical mystery, a killer disease that grieving Mormon pioneers could only blame on "teething" as it claimed hundreds of their children.

For 15 years, the Salt Lake city-county health director has tried to identify the enigmatic ailment he stumbled on in 19th century death records locked away in the department's vault."When I get burdened with my work, I go down and read through the old records. I was curious what the medical problems were in the pioneer days," Gibbons said.

"One day, I started seeing these `teething' deaths," Gibbons said. "Teething is not a cause of death . . . and we wonder what it was that caused practitioners back then to identify it as such."

Assisted by staff physician C. Kent Hebdon, a former clinical pathologist, Gibbons found that between 1847 - the year Mormon settlers began arriving in the Salt Lake Valley - and 1881, a total of 521 infant deaths were attributed to teething or related conditions.

In an article published in this month's Western Journal of Medicine, Gibbons and Hebdon admit they have been unable to explain the phenomenon - and they invite other health professionals to join in solving the riddle.

A search of medical literature, interviews with historians and pediatricians and study of other early records failed to provide clues to the actual cause of the deaths, Gibbons and Hebdon write.

An early candidate was sudden infant death syndrome, but Gibbons said it doesn't fit the circumstances. While the average age of the teething death victims was 13 months, most studies indicate SIDS usually occurs before 6 months.

Further, the teething deaths have a strong seasonal component. Records show most of them occurred between August and December, with the peak in October.

Modern-day Utah SIDS cases peak in January but are otherwise fairly constant throughout the year, Gibbons said.

In the late 1800s, corresponding to a decline in the citing of teething as a cause of death, "cholera infantium" appeared increasingly in mortality records.

The average age of cholera infantium victims was similar to that of the teething victims, but the deaths peaked in August, two months earlier than those attributed to teething.

Gibbons and Hebdon also concluded that the vague cholera infantium, which eludes an exact definition, likely was not SIDS. They also dismissed other leading child-killing illnesses of the time such as infantile diarrhea, diphtheria and typhoid.

"We just don't know what it is," Gibbons said. "But it does appear to have been one disease entity because it consistently occurred at one specific time period each year."

While rare, there are other references in medical literature and lore to teething-related ailments causing serious illness or death, Gibbons and Hebdon noted.

Hippocrates warned 2,400 years ago that teething children could suffer from fever, convulsions and diarrhea. In 1732, Scottish physician John Arbuthnot estimated that more than a 10th of children died while teething.

Gibbons' and Hebdon's research also revealed that "teething convulsions" were listed as the cause of death in a small group of English children between 1947 and 1979.

They even found a 1905 American home health care book that recommended lancing the swollen gums of teething children to correct a "blunder of nature."

While interesting, the references fail to shed much light on the Utah mystery.

For the 61-year-old Gibbons, finding a scientific explanation for what killed pioneer children has become something more than the historical novelty it first was. It's a personal quest.

"I plan to stay on the trail," he said. "I'm just beginning by publishing this."