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SIDS, infection could be linked

Researchers study E. coli byproduct

Friday, April 26, 2002

By Emma Ross, The Associated Press

MILAN, Italy -- Sudden Infant Death Syndrome, in which apparently healthy babies die inexplicably in their cribs, may be linked to infection with a common bacterium, preliminary research suggests.

Researchers told a conference on infectious diseases yesterday that a shock-producing byproduct of E. coli was found in the blood of all SIDS babies tested, but in none of the infants used as a comparison.

Experts not connected with the research said the toxic infection theory is plausible.

SIDS describes unexpected deaths that autopsies can't explain. Despite decades of research, scientists remain mystified by crib death, the top killer of babies between 1 month and 1 year-old in the industrialized world.

Among the threats it has been tied to are sleeping position, passive smoke exposure and genetic vulnerability. Infection is not a new idea, but this is the first time the specific E. coli protein has been implicated.

Many researchers favor a theory that brain-stem birth defects somehow affect arousal reflexes, so that babies don't wake up when breathing, heart rate, blood pressure or temperature problems arise. But some experts believe that such brain abnormalities may not be enough to cause death on their own.

"Mainstream researchers have concentrated on respiratory obstruction as a possible mechanism, without any evidence that would support such a mode of death," said Dr. Paul Goldwater, who presented his study at the European Congress of Clinical Microbiology and Infectious Diseases in Milan.

"Those researchers ignored autopsy findings that consistently show wet, heavy lungs in SIDS babies. This is never seen" in cases of suffocation, said Goldwater, a researcher at the Women's and Children's Hospital in North Adelaide, Australia.

Such a lung condition is often seen in cases of infection. Autopsies also consistently show small hemorrhages on the heart and lungs -- which is rare in suffocation -- and the blood of SIDS babies is unclotted, which is something never seen in suffocation cases, he added.

Furthermore, he said, SIDS deaths captured on medical monitors have shown that these babies died of a shock-like process, Goldwater said.

"The serum from babies who have died of SIDS is toxic to chick embryos and mice -- indicating the presence of a toxin," he said.

In his study, Goldwater tested the blood of 68 SIDS babies and 60 other babies -- some of whom had died of other causes, and some of whom were alive -- for infections that could explain the autopsy findings in SIDS babies.

He started with the common gut germ E. coli because varieties from SIDS cases are more often toxic to cells grown in a lab than are varieties found in healthy babies.

Sometimes, E. coli bacteria produce a protein called curlin, which scientists suspect may help the bacteria compete for a foothold in the competitive germ environment in the intestines, he noted.

The bacteria itself was found in the intestines of all the SIDS babies, but only in 80 percent of the healthy babies. However, curlin was detected in the bloodstream of all 68 of the SIDS babies and none of the others, Goldwater said.

"This indicated that curlin could be responsible for SIDS deaths, given the fact that curlin causes shock in laboratory mice," Goldwater said.

Dr. Carl Hunt, director of the National Research Center for Sleep Disorders at the U.S. National Heart, Lung and Blood Institute, said Goldwater's findings do not conflict with the popular brain-stem defect theory.

The deaths might be triggered by infection, Hunt said, or might be due to a combination of genetic factors, such as a brain stem defect or an impaired immune system, and environmental factors, such as the baby sleeping on its stomach or breathing in cigarette fumes.

"The basic theory that some serious, overwhelming acutely acquired infection is the cause of SIDS is a legitimate hypothesis," Hunt said. "What we recognize today as SIDS may have a variety of different causes in individual infants. The extent to which infection does play a role in SIDS and in what percentage of SIDS it might play a role are important questions."

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