Why is it that a company is presumed to be liable for the mesothelioma of one of it's previous employees if it can be shown that they were exposed to above background levels of asbestos? There are a number of other causes of mesothelioma (radiation, some paints, sv40 virus, family genetics, as well as the unknown causes which result in a 1:1,000,000 spontaneous rate). It seems on the surface to be an argument which merely begs the question. Low levels of asbestos exposure cause mesothelioma because we have seen mesothelioma cases with low levels of asbestos in their lungs (which of course is only relevant if you've already concluded that low levels of asbestos can cause mesothelioma).
I'm having trouble understanding how such a situation ever became so strong without anyone having mounted a successful defense - i.e. that the litigant's mesothelioma could have been caused by any number of agents and so the company could not be held responsible, simply because of the possibility that their negligence could have been the cause.
Basically, it is still being argued whether low levels of exposure to asbestos can even cause mesothelioma at all, and yet it seems a huge (and seemingly impenetrable) quantity of litigation is built on the premise that it definitely does. Have there been any successful defenses in litigation based on the fact that mesothelioma has a number of non-asbestos causes?