[DanBC]

Here's one study that found potential risk from aerosolised particles from flush toilets.

http://www.ncbi.nlm.nih.gov/pubmed/16033465

> Many individuals may be unaware of the risk of air-borne dissemination of microbes when flushing the toilet and the consequent surface contamination that may spread infection within the household, via direct surface-to-hand-to mouth contact. Some enteric viruses could persist in the air after toilet flushing and infection may be acquired after inhalation and swallowing.