Havelaar et al. (2000) were among the first to demonstrate a
systematic approach for comparing microbiological and chemical
risks in a quantitative manner using composite metrics to compare
risk and benefits of microbiological and chemical hazards with differing
disease endpoints. They estimated the beneficial effects of
reducing the load of the protozoic parasite Cryptosporidium parvum
in Dutch drinking water vs. the health risks of carcinogenic bromate
(an ozonation by-product) formation following drinking
water ozonation. They used probabilistic risk modelling to quantify
the chemical and microbiological risks, respectively, expressing
them in DALYs. The results from their models indicated that the
health benefits of reducing C. parvum outweigh the health loss
due to bromate formation by a factor of 10. Their study demonstrated
that the DALY could be used effectively to weigh health
risks and benefits of disease with differing endpoints and public
health impacts and to assess the net change in public health following
regulatory actions. Nevertheless, they conclude that gaps
in the available data for performing quantitative analysis and
assessing DALYs are large, and can be expected to result in a large
degree of uncertainty, hampering the precision of quantitative
assessments (see discussion in Section 2.4).