Following is an overview of the 1998 UK Limerick Report regarding the toxic gas theory for crib death (the Richardson hypothesis). Contrary to publicity, the Report did not disprove the theory - in fact, it provides further confirmation of it.
BACKGROUND
At the end of 1994 the British Government faced huge potential legal claims by bereaved parents. In the 1980s the Government had required manufacturers to include a fire retardant in cot mattresses, and had approved antimony trioxide for the purpose. The result was the generation within crib mattresses of stibine gas, which caused thousands of cot deaths. If the Limerick Report had supported the toxic gas theory for cot death, the British Government would have been liable for millions of pounds in damages.
What did the Limerick Committee investigate?
They investigated whether certain toxic gases are generated from fire retardant chemicals contained in PVC-covered crib mattresses.
Was this a full investigation of the toxic gas theory for crib death?
No. It had serious limitations:
The Committee did not investigate any mattresses other than those covered with PVC. They did not investigate natural products used as bedding (despite the fact that many crib deaths occur on such materials, e.g. sheepskins). They focused on only one of the three relevant gases (stibine).
Is the Limerick Report relevant in New Zealand?
Largely, no. This is because PVC-covered mattresses are very rarely used in New Zealand. Sheepskins (which are frequently used as baby bedding in New Zealand) were specifically excluded from the study. New Zealand mattresses very rarely contain fire retardants. The toxic gases most likely to be generated from New Zealand baby bedding (phosphines and arsines) were not focused on in the study.
How then does the Report provide confirmation of the toxic gas theory?
It confirms (yet again) the gas generation which causes crib death: the Committee achieved generation of a form of stibine. Other researchers had already proved the generation of all three gases: phosphines from phosphorus, arsines from arsenic and stibines from antimony.
But the Report's conclusion states that the toxic gas theory is unsubstantiated. Why?
Although the Committee had replicated the toxic gas generation, they said such gas was not the cause of crib death. This conclusion was based on a large number of errors and irrelevancies. For example:
The Report stated that one particular fungus which can cause gas generation (S. brevicaulis) was not found on any mattresses on which babies had died of cot death. Irrelevant. The Committee found S. brevicaulis and many other micro-organisms on crib mattresses - and a number of these are capable of generating toxic gas if phosphorus, arsenic or antimony are present in a mattress. Whether babies had died on the mattresses tested by the Committee is immaterial.
Household fungi become established in nearly every mattress which is slept on, and in underbedding which is washed infrequently.
The Report stated that what Richardson had identified as a fungus was actually bacteria. Irrelevant. Bacteria as well as fungi can generate toxic gas from the chemicals concerned.
The Report stated that while toxic gas was produced under laboratory conditions, no gas could be produced in cot conditions. Irrelevant. Gas generation has already been achieved in crib conditions, and failure by the Limerick Committee to do so doesn't negate this fact.
Various researchers have found it difficult to achieve gas generation consistently using media with a neutral pH. But the pH of a cot mattress is often higher, owing to the conversion of urea to ammonia. Experiments carried out using high pH (say, 10) have achieved more consistent gas generation. In these tests fungus flourished and the amount of gas produced was greater than at neutral pH.
The Report stated that cot death babies did not show the typical physiological effects of phosphine, arsine or stibine poisoning, e.g. haemolysis and pulmonary oedema. Of course they didn't. Babies die so quickly from this type of poisoning that these effects don't have time to develop.
Haemolysis, for example, takes many hours to develop; so does pulmonary oedema. But this gaseous poisoning can kill a baby within minutes.
The toxicological data contained in the Report relates to adults and older children. None of it relates to babies - and it is well known that babies' blood and physiological responses differ materially from those of older children and adults.
The Report stated that crib death babies had the same amount of antimony in their body tissue as babies who had died of other causes. Wrong. Research carried out in 1994 showed that post mortem body tissue of crib death babies contained many times more antimony than tissue of babies who had died of other causes.
The Report stated that antimony present in the tissue of crib death babies could have come from many sources other than their mattresses. Wrong. The same 1994 research showed that the body tissue of babies who had died of causes other than crib death contained no detectable antimony (or in one case very little). If the Report were correct, there would have been similar amounts of antimony in the tissue of all the babies tested, whether they had died of crib death or of other causes.
The Report stated that the introduction of antimony and phosphorus into mattresses in Britain did not coincide with a rise in the cot death rate. Wrong. These chemicals were first introduced into crib mattresses in the early 1950s, and the British crib death rate increased steadily from that time onwards. (In fact the term "cot death" was coined in 1954 as a result of the marked increase in the number of such deaths.)
The highest crib death rate in Britain (2.3 deaths per 1000 live births in 1986-1988) coincided with the highest concentration of antimony in crib mattresses. The British Government had required a fire retardant to be incorporated in crib mattresses by 1988. Manufacturers were given four years' warning and during this period moved towards compliance with the new standard.
The Report stated that the steepest fall in cot deaths in Britain occurred when antimony was very prevalent in crib mattresses and coincided with the "Back to Sleep" campaign. Highly misleading. Certainly the British crib death rate fell while the amount of antimony in mattresses was high - but that was because from mid-1989 onwards parents took preventive measures against toxic gas generated in their babies' mattresses. Furthermore, manufacturers began to remove antimony from mattresses.
In June 1989 the toxic gas theory was publicized nationwide and the crib death rate immediately began to fall (see graph). It had fallen 38 % (to about 1.4 deaths per 1000 live births) by the time "Back to Sleep" was launched in December 1991 - two-and-a-half years later. The fall was steepest following the commencement of "Back to Sleep" because that campaign added to the success already being achieved by advice based on the toxic gas theory.
What about the claim in the Report that three babies have died of crib death on polythene-wrapped mattresses?
This claim is unsubstantiated. The types and thicknesses of the plastic are not known. Was it thick, clear polythene (safe) or thin or coloured polythene (unsafe)? Was there bedding containing phosphorus, arsenic or antimony on top of the plastic? Were sheepskins used? Or mattress protectors? These questions have not been answered, and without this information the claim is not valid.
In February 2000 Dr Peter Fleming, a co-author of the Limerick Report, stated that the claim that three babies had died of crib death on polythene-covered mattresses could not be substantiated.
Are there other findings which support the toxic gas theory?
Yes. For example:
Scottish research has proved that the crib death rate rises as mattresses are re-used from one baby to the next. This is because micro-organisms become better established in a mattress as it is used. When re-use commences, toxic gas is generated sooner and in greater volume. Statistics show that the crib death rate jumps from first babies to second babies; and jumps again from second babies to third babies; and rises still further for later babies. The reason is that parents frequently buy a new mattress for their first baby and then re-use it for subsequent babies. Research in the USA has reported that crib death babies show neurochemical deficits relating to heart function and breathing. This is accounted for by the fact that phosphines, arsines and stibines are all "nerve gases". They shut down the central nervous system, causing cessation of heart and breathing functions. (This is why crib death babies do not show any apparent symptoms.)
The conclusions of the Limerick Report should be disregarded. Other researchers have disproved them; and so has the practical experience of mattress-wrapping in New Zealand. Since late 1994 many tens of thousands of New Zealand parents have wrapped their babies' mattresses for cot death prevention, and since that time the New Zealand crib death rate has fallen markedly. The practical experience of mattress-wrapping proves the toxic gas theory for crib death. If mattress-wrapping did not prevent crib death, many deaths would have occurred by now on polythene-wrapped mattresses.
