SIDS Recurrence Overestimated, Researchers Say

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DANBY WISKE, England -- The recurrence of sudden infant death syndrome (SIDS) within families may be less common than reported, according to a literature review.

DANBY WISKE, England, June 12 -- The recurrence of sudden infant death syndrome (SIDS) within families may be less common than reported, according to a literature review.

Since 1970, eight studies have reported repeat SIDS incidence, but all eight have failed on accuracy of diagnosis, adequacy of investigation, or comparisons with the correct control group, said Christopher J. Bacon, M.B.B.Chir., a retired consultant pediatrician here, and colleagues.

"We think that all these studies are flawed in ways that will mostly have caused overestimation of the risk of SIDS recurrence," they wrote online in the Archives of Disease in Childhood.

The risk that parents who have lost one child to SIDS will lose another is likely less than 1 in 500, they said. The earlier studies had shown a 1.7- to 10.1-fold increased relative risk in these infants.

"Families whose initial death was fully investigated and who have no major risk factors can be advised that, although the risk of a second death may be slightly increased, it remains very small," the researchers said.

For the review, Dr. Bacon and colleagues examined the English-language literature since 1970 for population-based "sudden infant death" and "cot death" studies in families with a prior SIDS death. Case reports were excluded.

The researchers defined SIDS as unexpected, natural infant deaths without a specific cause.

Each of the eight studies the researchers found was evaluated for the accuracy of its SIDS recurrence estimate.

Complete and accurate ascertainment of cases was determined based on whether the study included all index cases in a defined population and period and identified all sibling cases prospectively or from official records.

One study did not meet the criteria for accurate ascertainment of index cases and three only partially met the criteria. Two did not measure up for ascertainment of sibling cases while another two did so only partially.

The effect was likely overestimation of SIDS recurrence in two studies and underestimation in a third, the researchers said.

Thoroughness of investigation was determined based on whether a study included an autopsy and adequate testing for familial diseases, such as fatty acid oxidation defects, and whether homicide was adequately ruled out by a death scene investigation and confidential inquiry.

Four studies only partially met the autopsy criterion. Only one study even partially met the criterion for adequate familial testing. That may not be surprising, the researchers said: Early studies did not examine for familial diseases not yet known to be implicated.

"Medium-chain acyl-coenzyme A dehydrogenase deficiency, the best known, was recognized as such only in 1984," the investigators noted.

"Even today they may not be excluded satisfactorily because of the impracticality and expense of doing all the tests," they added.

Only one study even partially met criteria for an adequate evaluation of covert homicide, likely for the same reasons, the researchers said. It was not widely acknowledged as a possible cause of sudden, unexpected infant death until the 1980s, they said.

The studies were also evaluated for whether they matched the comparison group for risk of SIDS. None did.

But, this only became an issue in 2000 when a study found a 40-fold difference in risk between low-risk and high-risk families (multiparous young mother, no job, smoker in the household).

"Without this stratification, repeat SIDS in high-risk families will give a false impression of an increased risk for the population as a whole, even if the rates in each subgroup have stayed the same," they wrote.

The researchers still concluded that "a family's risk for a second SIDS death is probably greater than the risk for a first death for their subgroup, but that the increase cannot be quantified and is almost certainly less than that suggested by most of these studies."

They warned that "great caution" is needed in addressing this controversial and sensitive subject, particularly in the courts when there is little good evidence.

For parents who are anxious about the chances of SIDS recurrence for future children, the researchers suggest that physicians should review the details of the death to ensure adequate exclusion of familial disease and recommend tests on family members if appropriate.

"Families at high risk, whose infants are more vulnerable to death from other causes as well as from SIDS, should be identified and given all possible support," they added.