Cryptosporidiosis is a protozoan parasitic infection that most commonly presents as gastroenteritis and less commonly infects the respiratory and biliary tracts. Enteric symptoms usually include diarrhoea, bloating, cramping, abdominal pain, vomiting and fever. The disease is usually mild and self-limiting but in immunocompromised individuals is prolonged and can lead to death. The infective dose in humans is low and the incubation period ranges from one to 12 days, with an average of seven days. The infectious period lasts from the onset of symptoms, as the oocysts are excreted in the stool, until several weeks after symptoms resolve.

The oocysts are widespread and may remain infective outside the body for two to six months, particularly if the environment is moist. They are highly resistant to standard levels of chemical disinfection of water such as chlorine. Outbreaks have been reported in day care centres, and been associated with drinking water, recreational water (waterslides, swimming pools and lakes) and consumption of contaminated beverages. In Australia, increases in notifications tend to occur in the warmer months and over irregular cycles, with more than 3000 cases notified in Australia in 2002, 2005 and 2006.

Cryptosporidiosis became notifiable in both Australia and Victoria in 2001, with more than 15,000 cases notified between 2002 and 2009. The aim of this study was to describe the epidemiology of notified cases of cryptosporidiosis in Victoria for the period 2001 to 2009 in terms of age, sex, location and season.