Infants who share a bed with other children are at a higher risk of sudden infant death syndrome (SIDS) than are other infants, according to the most recent analysis of a study of predominantly African American SIDS deaths in Chicago.

The analysis, appearing in the May, 2003 "Pediatrics", also found that two known risk factors for SIDS -- sleeping on soft bedding and sleeping on the stomach -- pose a far greater risk of SIDS when they occur together than the sum of both risk factors added together would indicate. This analysis confirms several international studies reporting that SIDS risk was lower among infants put to bed with a pacifier and reinforced earlier findings that sleeping on a sofa also increases infants' risk of SIDS.

The study was supported by the National Institute of Child Health and Human Development (NICHD) and the National Institute on Deafness and other Communication Disorders (NIDCD), both at the National Institutes of Health (NIH), as well as the Centers for Disease Control and Prevention (CDC). NIH and CDC are agencies of the U.S. Department of Health and Human Services.

The researchers studied all infants from the ages of birth to one year who had died of SIDS in Chicago, Illinois, between November 1993 and April 1996. There were 260 SIDS deaths during that time.

"This study provides important new information regarding SIDS risk factors," said Duane Alexander, M.D., Director of the NICHD. "The next step is to get this information to the parents and families who can use it to reduce the risk of SIDS among their own infants."

"The SIDS rate for African-American babies is more than twice that for white infants," said CDC Director Dr. Julie Gerberding. "Families need counseling on ways to reduce the risk of SIDS. For example, they need to know they should avoid putting an infant to sleep with other children."

The Chicago Infant Mortality Study was directed by Fern R. Hauck, M.D. M.S., currently of the University of Virginia Health System.

"Our study found a dramatic increase in SIDS risk for prone sleeping on soft surfaces, highlighting the need to eliminate these unsafe sleep practices," said Dr. Hauck. "Additionally, infants should never be placed to sleep on a couch with anyone or in a bed with other children."

The researchers compared information about each SIDS case to information about a control infant -- a living infant of comparable age, who was from the same racial and or ethnic group, and who had a similar birth weight. All of the SIDS deaths were evaluated by the Cook County Medical Examiner's Office; autopsies had been conducted to rule out other causes of death. Death scene investigators conducted interviews about circumstances surrounding the deaths. The researchers used the NICHD definition of SIDS: "the sudden death of an infant under one year of age, which remains unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history."

Infants who died of SIDS were 5.4 times more likely to have shared a bed with other children than were the control infants. Sleeping with the mother alone or mother and father was associated with an increased risk of SIDS, but this finding was not statistically significant. The study concluded "the risk was primarily associated with bed sharing when the infant was sleeping with people other than the parents." The researchers also reported that sleeping with the mother alone did not reduce infants' risk of SIDS, as some researchers have concluded on the basis of earlier studies.

The researchers noted that sleeping on the stomach, and sleeping on soft bedding -- both known to increase the risk of SIDS independently -- posed a much greater risk for SIDS when occurring together than might be expected. For example, soft bedding appeared to pose 5 times the risk of SIDS as firm bedding; sleeping on the stomach increased the risk of SIDS 2.4 times. Yet infants who slept stomach down on soft bedding had 21 times the risk of SIDS as infants who slept on the back on firm bedding.

Of the SIDS cases, 15 were found to have slept on a sofa the last time they were placed to sleep. The researchers do not know why sleeping on a sofa would increase the risk of SIDS more than would sleeping on a bed, yet warn that the practice appears to be highly dangerous.

The study authors concluded that physicians should counsel new parents not only about the benefits of placing infants to sleep on their backs, but also about the risk their study had uncovered.

"Parents are influenced strongly by their physicians in choosing the sleep position for their infants," they wrote. "Other infant care practices, such as bed sharing and use of soft bedding, may also be influenced by medical providers, particularly if reinforced by the media."

To reduce the racial disparity in SIDS rates, the authors advised taking families' economic circumstances into consideration. For example, some parents may not be able to afford firmer mattresses or to have enough beds for all their family members. The authors called for research on how best to meet these needs.

"On the basis of the findings of this study, they [parents] should receive instruction that emphasizes supine sleeping, firm bedding, not using pillows, and not sharing a bed with other children or sleeping with another person on a sofa, while being sensitive to parental concerns and cultural traditions."

The current study is part of a body of research sponsored by the NICHD on infant sleep practices and the causes of

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