Medical scientists, theorising over the years about what caused the some 600 cases each year, have looked at such factors as babies sleeping on their stomachs, or being too warm, or possibly the victim of an infection - and even a delayed result of caffeine or nicotine during the mother's pregnancy.
But now scientists at Goettingen University, Germany are collecting possible proof for a further - but still controversial - risk factor.
Their studies have shown from the autopsies conducted on 113 dead infants since 1994 that almost one-third had some form of toxic botulism germs in their intestines, blood or liver.
Even the tiniest amount of the toxins produced by bacteria can lead to death by asphyxiation or by paralysis of the muscles.
"This is very unusual. Twenty years ago botulism was discovered in only 1 percent of the cases," notes Professor Klaus-Steffen Saternus, director of the Institute of Forensic Medicine in Goettingen.
He adds that the increase cannot alone be attributed to improved methods of detection.
Now he is conducting tests on animals to see whether the toxins taken from babies' organs are really biologically active.
He injected mice with the poison and then, in many cases, was able to save them with an antidote.
But experts are heatedly debating the findings of the study.
"Since 1978 there have repeatedly been studies about botulism and sudden crib death," says Thomas Bajanowski of the forensic medicine department at Muenster University.
The studies "had led to completely contradictory results", he adds, while asserting that the Goettingen findings could be attacked on scientific grounds because of an inadequate control group.
"There are well beyond 100 hypotheses for the causes of infant deaths," Bajanowski says.
"What is probable is that several combined factors are the cause."
Could come from garden compost
In Muenster, a long-term study through the year 2004 is being sponsored by the German Health Ministry to investigate some 600 dead infants for possible sudden crib death.
Saternus and a veterinary medical scientist, Professor Helge Boehnel, suspect that a possible source for the botulism reaching an infant is from garden compost and special flowerbed soil.
They note that in many samples taken from composts the dangerous bacteria germ "clostridium botulinum" - it survives as a tiny spore - had been found.
However, at this stage it is still a hypothesis that the spore reaches children via the air.
"Naturally we are asking ourselves, 'how do the spores get inside the infants if they are being completely breast-fed by their mothers and their baby food is okay?'," Saternus says.
Green bins maybe not that great
He notes that such spores can be found in honey, but that none of the cases showed that the infants had been fed honey.
Boehnel, for his part, carried out a research study in Europe which analysed types of compost and flower bed soil gained from garbage processed in so-called "green bins".
The study took place in the state of Lower Saxony.
"In half of the samples we found the dangerous spores. These are increasingly being brought into the bio-cycle and can survive 100 to 200 years in the soil," he said.
From the spores, bacteria germs can evolve which can set free the toxic botulins, which in turn can block the messages sent between the nerves and the muscles.
Boehnel now is coming to the conclusion that "compost from the 'green bins' is not safe".
Danger is being played down
He said the sale of the bins - popular among ecologically-aware hobby gardeners in Germany - should be stopped until all composting processes have been tested for the botulism agent.
Moreover, Boehnel accuses the Federal Environmental Agency (FEA) in Berlin of long having been aware of the danger and of playing it down.
Agency spokesperson Karsten Klenner rejects this.
"We are taking this very seriously and are not putting it on the back burner," he said.
We need more proof
And Regina Szewzyk, an expert at FEA, also counters Boehnel's accusations with those of her own.
"Boehnel has found agents in the compost samples, but no toxin. And he doesn't say how high the concentration is."
Clostridia bacteria are also found in natural environments such as lakes, the earth, or even simple house dust. Poultry droppings and the liquid manure of pigs and cattle can contain the bacteria.
"We are not living in a sterile environment," Szewzyk observes.
He points out that the environmental agency has commissioned Boehnel to develop a standardised test for determining the existence of botulism agents in compost. - Sapa-DPA