On its way to supermarket shelves, bagged spinach passes from field to packing plant to store, with several opportunities along the journey for it to become contaminated with deadly E. coli bacteria.

This complex chain is making it hard to identify the precise source of the outbreak that has killed one person and sickened at least 113 others around the country, according to the Associated Press.

Food health experts say the germ can be spread a multitude of ways — by manure, by contaminated irrigation water, by farmhands relieving themselves in the field, by inadequate washing by processors, by insufficient refrigeration that promotes the growth of bacteria in sealed bags of salad greens.

California agricultural regulations require that toilet and handwashing facilities for farmworkers be located within one-quarter mile or a five-minute walk from the work site, with one toilet per 20 employees of each gender. Employers whose workers use fields instead of the bathrooms can face fines of up to several thousand dollars.

In addition, safety measures exist all along the production chain, from chlorinated water to refrigerated trucks for transport.

Yet whatever precautionary measures are in place, industry watchers say you can only do so much to control nature.