An analysis published in this week's BMJ is set to re-open the debate over sudden unexpected infant death (cot death).
The Lancet recently published a study on repeat infant deaths in 46 families, which suggested that almost 90% of second deaths in the same family are natural.
These findings contrasted with earlier studies, which found a much higher proportion of repeat cot deaths were probably homicide. Yet the Lancet study has proved very influential, being accepted by bodies such as the American Academy of Pediatrics.
In December 2006, the BMJ questioned the way these deaths were classified in the study.
Today the BMJ publishes a re-analysis of the data by two senior (now retired) paediatricians, Christopher Bacon and Edmund Hey. They reviewed the 46 second deaths in the original study to see how many might reasonably be regarded as undetermined.
They suggest that, in the three families in the original study in which both deaths were attributed to specific natural causes, one death should be regarded as undetermined.
In 18 families in the original study, both deaths were attributed to sudden infant death syndrome. The authors stated that all these families were at high risk of cot death and that the second deaths exhibited many untoward features, such as violent family relationships, pathology findings suggestive of asphyxia, and parental mental health problems.
Although Bacon and Hey do not suggest that violence in the family, for example, necessarily implies that a baby's death was unnatural, they believe that when a family has two unexplained deaths this possibility at least has to be considered and may sometimes be true. They therefore estimate that a third of these deaths might be classed as undetermined.
For 13 families in the study, information on the second death was incomplete. The original authors classified all these cases as natural, though they acknowledged that the information was insufficient to enable them to distinguish between sudden infant death syndrome and a specific natural cause.
But Bacon and Hey argue that it seems illogical to exclude covert homicide when there is not enough information to exclude a specific natural cause. They categorise all 13 cases as undetermined.
There were six further cases that could not be reviewed because the Lancet paper gave no details about them.
Overall, the re-analysis of these second deaths categorises 13% as probably unnatural, 43% as probably natural (although this includes the six cases they could not review) and 43% as undetermined. This contrasts with the original study that 87% of the deaths were natural, but is closer to the findings of previous studies that suggested about two fifths of repeat deaths probably resulted from homicide.
Bacon and Hey stress that their purpose is not to second guess the original authors, but they argue that using a dichotomy of natural or unnatural is unhelpful and more likely to be erroneous. They acknowledge the paper's value in helping to avert unjustified suspicion of parents, but they are concerned that it may also lead to mistakes in child protection.
Uncertainty may be uncomfortable, they add, but it is truer to reality, more conducive to scientific inquiry, and safer for children than a dogmatic stance at either pole.
"We would encourage professionals to keep an open mind in assessing unexplained infant deaths, to be aware of the difficulties in diagnosis, and to try to keep a balance between the need to support parents and the need to protect children," they conclude.