Aim: Gastro-intestinal infections are widespread in the community and have considerable economic consequences. In this study, we followed chains of infection from a public toilet scenario, looking at infection risks by correlating the transmission of bacteria, fungi and viruses to our current knowledge of infectious doses. Methods and Results: Transmission of Escherichia coli, Bacillus atrophaeus spores, Candida albicans and bacteriophage MS2 from hands to surfaces was examined in a transmission model, that is toilet brush, door handle to water tap. The load of viable pathogens was significantly reduced during transfer from hands to objects. Nevertheless, it was shown that pathogens were successfully transferred to other people in contagious doses by contact with contaminated surfaces. Conclusions: Our results suggest that infection risks are mainly dependent on current infectious doses of pathogens. For enteritic viruses or bacteria, for example Norovirus or EHEC, only a few particles or cells are sufficient for infection in public lavatories, thus bearing a high risk of infection for other persons. However, there seems to be only a low probability of becoming infected with pathogens that have a high infectious dose whilst sharing the same bathroom. Significance and Impact of the Study: The transmission model for microorganisms enables a risk assessment of gastro-intestinal infections on the basis of a practical approach.