Background and epidemiology: Safe

drinking water is one of the most sig-nificant public health advances in the past 100 years,1 yet over 1 billion peo-ple lack safe drinking water and 2.4 bil-lion lack adequate sanitation.2 Trav-ellers are at risk of waterborne illness if they cannot ensure safe drinking water and adequate sanitation, but simple precautions minimize the risk. Worldwide, waterborne illness from contaminated water and unsanitary conditions accounts for 1 billion cases of diarrhea and an estimated 10–25 mil-lion deaths each year, including 95 % of deaths among children under the age of 5 years.3 The most common organ-isms causing such illness are enterotox-igenic species of Escherichia coli, Salmo-nella, Shigella, Giardia, Cryptosporidium and hepatitis A virus.4,5 Permanent im-munity does not usually develop against most pathogens, and reinfection can occur. The global burden of diarrhea is rel-evant because the local population acts as a pathogen reservoir. One or more pathogens are found in the stool of the majority of travellers from industrial-ized countries who become ill in devel-oping countries, which makes “trav-eller’s diarrhea ” the most common travel-related illness.6,7 The risk of waterborne illness while travelling depends on the number of or-ganisms consumed, the organism’s viru-lence, the host’s defenses and the desti-nation. As few as 10–100 Giardia or Cryptosporidium organisms can cause infection, as compared with 1000 o