Since public health messages to lay sleeping infants on their backs have become pervasive, the risk factor profile for sudden infant death syndrome (SIDS) has changed in recent years, researchers said.

Sharing a bed with a parent has become a prominent risk and was present in about 40% of cases, Henry Krous, MD, of Rady Children’s Hospital in San Diego, and colleagues reported in Pediatrics.

They also warned that the condition appears to rise from a combination of several risk factors, not just one.

“Risk reduction campaigns emphasizing the importance of avoiding multiple and simultaneous risks are essential to prevent SIDS,” they wrote. In 1994, the National Institute of Child Health and Development launched Back-to-Sleep, a public health campaign to raise awareness that babies should sleep on their backs, not on their stomachs, as being in the “prone” position increased their risk of SIDS. SIDS rates in the U.S. fell significantly after the campaign was initiated, dropping more than 50% within the first 10 years. But since then, rates have stalled at about 0.53 per 1,000 births, and SIDS remains the leading cause of postneonatal infant mortality. In an effort to identify other risk factors to target, Krous and colleagues looked at records of 568 SIDS deaths in the San Diego SIDS/Sudden Unexplained Death in Childhood Research Project from 1991 through 2008. They split the data into two time periods, before and after the launch of Back-to-Sleep. The percentage of SIDS victims found in the prone position fell from 84% to 48.5% between 1991-1993 and 1996-2008 (P<0.001). However, the proportion of SIDS infants that had shared a bed with a parent rose from 19.2% to 37.9% during that time (P<0.001) and was especially pronounced among infants less than 2 months old (29% versus 63.8%). More SIDS infants were also born premature, rising from 20% to 29% after the public health campaign (P=0.05). The researchers found the percentage of SIDS infants with symptoms of upper respiratory tract infection fell, from 46.6% to 24.8% (P<0.001). Almost all SIDS infants (99%) had at least one risk factor for the condition, and 57% had at least two extrinsic and one intrinsic risk factor; only 5% had no extrinsic risk factors. There were no significant correlations between specific risk factors; rather, any combination of risks raises the odds of SIDS, Krous and colleagues wrote. They concluded that risk reduction campaigns that "emphasize the importance of avoiding multiple and simultaneous SIDS risks are essential" for prevention. Onajovwe Fofah, MD, a neonatologist at UMDNJ's University Hospital in Newark, N.J., who wasn't involved in the study, said looking for a constellation of risk factors is key. "You want to focus on not just a single risk factor, but look at your population and look at the multiple risk factors and the ones that might exist simultaneously, and target your [patient] education towards that," Fofah told MedPage Today. Still, to prevent SIDS, Betty McEntire, PhD, executive director of the American SIDS Institute in Naples, Fla., said the "resounding message" to new mothers is to "place the infant on his back in a bare crib, by the mother's bed. And avoid smoking before and after birth." The study was limited by a potential for reporting bias and a potential lack of generalizability, as there was a large proportion of Hispanic patients in the San Diego sample.