FOR THE SOLICITOR SALLY CLARK, it was, quite literally, a damning statistic. The chances of two babies in the same family becoming victims of cot death were one in 73 million, according to the paediatrician Professor Sir Roy Meadow.
To jurors, it was a coincidence too far and meant that Clark must be guilty of double murder. Two months after her conviction in 1999, in an editorial entitled “Conviction by mathematical error?”, the British Medical Journal revealed the unease felt by the medical profession at Meadow’s calculation. He had taken the odds of one cot death in an affluent, middle-class family like the Clarks — one in 8,500 — and squared them. The BMJ argued that the odds should never have been squared, that the true odds of such a double tragedy were still one in 8,500, and concluded that “with this mathematical error prominent the conviction is unsafe”. Yet it would be another two years before Clark’s conviction was finally overturned.
Recent research in Sudden Infant Death Syndrome (SIDS), as cot death is more formally known, suggests that genetics plays a role. Two years ago, Dr David Drucker, a microbiologist at Manchester University, discovered a particular gene that was common among cot death babies. This instantly raised the possibility that tragedy could strike twice in the same family.
In fact, Drucker’s work implied that a family that had already lost a child this way would be four times more likely to lose a second baby than a family who had never suffered a cot death. Contrary to recent speculation, the chances of a second cot death in the same family are not one in four, or even one in a hundred. Cot death is still rare — but in afflicted families, it is four times less rare, which is still unusual.
Cot death is more common in America but less common in Asian communities — a mystery which has so far defied explanation. Social class has an influence, with well-off families less at risk. This is likely to be due to a complex web of interrelated factors — for example, smoking, a known risk factor in cot death, is more prevalent among lower-income groups.
Drucker says that he, along with other scientists and statisticians who work in the field of cot death, were very unhappy with the evidence — particularly that crucial statistic — that secured Clark’s conviction.
Drucker has been an expert witness at two similar trials and has advised police on other cases. “What bothered me is that the person who gave that figure at the trial was not a statistician,” he says. “And as soon as genetics comes into it, it upsets any statistics. I do not think any statistician was happy with the way those probabilities were presented. Someone calculated that the chance of a double murder in a family like the Clarks is something like one in 500 million. So just on the basis of statistics, she should never have been convicted.”
He is also bothered about the way that pathologists are presented with information — sometimes the microbiological evidence is not disclosed, because it is deemed irrelevant.
The errant gene appears to have an effect on bacteria that have been implicated in cot death, which claims the life of one baby each day in the UK and is the most common cause of death in infants under one year old. This is why the microbiology reports were crucial to Clark winning her appeal; post-mortem tests showed that Harry, her eight-week-old son, had the deadly bacterium Staphylococcus aureus circulating in his body. It is the same bug responsible for MRSA, the hospital-acquired infection.
S. aureus is one of two bacteria implicated in cot death. The other is E coli. “Babies are most vulnerable to these bacteria at about two or three months of age because they are no longer getting antibodies from their mother and they have not developed their own immune systems,” Drucker says. “This is also when they appear to be most at risk from cot death.”
That coincidence led, 17 years ago, to Drucker carrying out detailed research into a possible microbiological link with cot death. He found that while the bacteria per se did not appear terribly dangerous, the toxins they produced could kill. Drucker, who was able to induce cot death in rats by giving them these toxins, found that cot-death babies tended to have particularly potent strains of both S. aureus and E. coli circulating in their bodies.
Drucker, whose work is partly funded by the Foundation for the Study of Infant Deaths, says a bacterial explanation probably accounts for the vast majority of deaths attributed to SIDS.
This would fit, he says, with evidence that both parental smoking and a baby sleeping on its front are additional risk factors. “Nicotine interacts with the bacteria to produce toxins that are a thousand times more potent,” he explains. “Sleeping positions have an effect on the way that fluid drains away. Sleeping on the front means that fluid collects in the nasal passages — these act like culture mediums for the bacteria.” In other words, nasal passages provide a perfect breeding ground for these deadly bacteria. Lying face-down also means the face is warmer, which again promotes the bacteria.
The cot-death gene appears to make the situation worse; it produces an anti-inflammatory chemical that is produced in response to the toxins. Basically, babies with this gene produce a feeble immune response to bacteria, making them particularly susceptible.
Meanwhile, Drucker is horrified that spurious statistics such as those used to convict Clark, and incomplete medical evidence, are being used not only to convict wrongly, but also to take children away from their families. As well as criminal cases, he is involved in cases in the family courts and describes the situation as a “complete scandal”. He would like to see microbiological evidence routinely taken from every baby who dies, so that a tragic case like the Clarks’s can be investigated more quickly. “We should keep the test results and freeze blood samples so that potential evidence is always there,” Drucker says. “It makes it easier to convict a guilty mother, and easier to acquit an innocent one. It is worth the extra money when you see what these murder trials cost.
“Sally Clark may be free but her life has been ruined by this. She will have nightmares for years to come. I have been involved in cases where I’ve been denied access to microbiology reports on the basis that the information is confidential and that for me to see it would be unethical. What is ethical about letting a mother go to jail for a murder she hasn’t committed?”
Key to a safe night's sleep
Foundation for the Study of Infant Deaths: helpline 0870-787 0554 (weekdays 9am to 11pm, weekends 6pm to 11pm).
