These illnesses develop in a small number of people as a consequence of a gastroenteritis infection. Irritable bowel syndrome causes ongoing disturbance of bowel function with varying degrees of severity. Guillain-Barré syndrome is a progressive paralysis that can be fatal. Patients often require intensive support, including respiratory assistance for days to weeks, until the paralysis passes. Reactive arthritis is characterised by pain in large joints and general debilitation, and usually lasts weeks to months.

While the features of these illnesses differ markedly, they are all caused by a reaction that occurs some time after the original infection. However, these illnesses can sometimes be a sequel to infections other than gastroenteritis. A summary of estimates of the numbers relating to these illnesses due to foodborne transmission is shown in Table 3.1. More information about the characteristics of the illnesses and details of the estimates are shown in Appendix A.

Estimates of the number of foodborne cases of the three sequel illnesses are based on a combination of Australian data and overseas studies that have followed large cohorts of people who had gastroenteritis caused by a confirmed pathogen. The studies documented the development of illnesses at a later date in a certain proportion of these people (see Appendix A).

Calculation of the number of cases of irritable bowel syndrome and reactive arthritis include incorporation of data on the incidence of certain types of bacterial gastroenteritis in Australia (Hall & the OzFoodNet Working Group 2004). The incidence of irritable bowel syndrome and reactive arthritis are derived by applying the relevant proportions of foodborne cases found in the overseas studies to the estimate of the total number of foodborne gastroenteritis cases caused by certain bacterial pathogens in Australia. There is a degree of uncertainty inherent in these estimates, due particularly to the paucity of data used to derive the estimates of bacterial gastroenteritis. This uncertainty is indicated in the 95% credible interval range given for each illness.

The estimate of the incidence of Guillain-Barré syndrome was based on the assumption that all cases would be admitted to hospital. Data from the National Hospital Morbidity Database gave the estimate of all cases of Guillain-Barré syndrome in Australia each year. The proportion of cases due to foodborne gastroenteritis estimated in the overseas studies was then applied to this.

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