The central problem addressed in this thesis related to establishing the biopsychosocial significance of H.pylori infection in adults with intellectual disability. H.pylori is an infectious gastrointestinal organism which causes gastritis, and, in a proportion of those infected, dyspepsia, peptic ulcer disease and gastric cancer. Within a biopsychosocial framework, clarification of the prevalence, risk factors, and consequences of infection, assessment of the impact of H.pylori eradication and determination of the most appropriate investigations were sought in a sample of 168 adults with intellectual disability who were followed for 12 months.
At baseline, each participant had a biopsychosocial evaluation including assessment of their levels of intellectual disability and maladaptive behaviour, and sociodemographic, environmental and medical circumstances. H.pylori status was assessed using both a faecal antigen test and serology. Participants who had current H.pylori infection were offered standard eradication treatment. Each participant was followed up at approximately four, nine and 12 months after baseline. At 12 months, each participant underwent another biopsychosocial evaluation and assessment of their H.pylori status using the carbon-14 urea breath, faecal antigen and serology tests.
The baseline biospychosocial characteristics of H.pylori positive and negative participants were compared to identify risk factors for, and consequences of infection. At 12 months, the participants were classified into four groups based on their change of H.pylori status from baseline: a change from positive to negative, remaining positive, remaining negative, a change from negative to positive. Change in the levels of intellectual disability, maladaptive behaviour and medical and gastrointestinal factors were compared across the four groups. In addition, factors that influenced the ability of participants to perform the various H.pylori tests were documented and the performance characteristics of the tests were calculated.
From the 75 currently, 53 previously and 40 never institutionalised participants, 70 (93.3%), 43 (81.1%), and 18 (45.0%), P < 0.01, respectively, had been infected with H.pylori at some time. The majority of H.pylori strains among those with a history of institutionalisation were CagA positive. The major independent risk factors for infection included a history of institutionalisation, institutionalisation at an earlier age, living with flatmates with hypersalivation or faecal incontinence, and a greater level of intellectual disability or maladaptive behaviour. Gastrointestinal symptoms did not distinguish H.pylori positive and negative participants. After treatment, the eradication rate of H.pylori infection was approximately 60% among participants from all residential settings. The overall reported side effect rate approached 30%) and was higher in those taking a greater number of medications or those with lower levels of ability.
There were no significant changes in participants' level of intellectual disability or maladaptive behaviour at 12 months, regardless of changes in H.pylori status. Participants tolerated performing the faecal antigen and serology tests equally well. Ability to perform these tests was not influenced by participants' levels of maladaptive behaviour or intellectual disability. In contrast, only one quarter of participants could perform the breath test and these individuals tended to have greater intellectual ability. At 12-months, using the serology test as a reference diagnostic test, the faecal antigen test had a sensitivity, specificity, positive and negative predictive value of 85.2%, 96.4%, 97.9%, 77.1%), respectively, while the urea breath test recorded values of 85.7%, 88.9%, 85.7%, 88.9%, respectively.
H.pylori infection appears to be almost universal among certain groups of people with intellectual disability. Moreover, H.pylori infection appears to be a relatively silent condition in this population, even in those with more virulent strains. These people are potentially at risk of significant but preventable morbidity and mortality from the disease consequences of this infection. The efficacy of standard treatment protocols appears lower than that in the general population and, in some, the side effects are more prominent. The diagnosis of H.pylori infection can be made with reasonable clinical certainty using the faecal antigen test (and serology under some conditions) or, in those with greater abilities, using the urea breath test. Although eradication of infection does not change the level of maladaptive behaviour or intellectual disability, it may reduce the risk of the disease consequences of H.pylori. Given the clinical silence of the infection, the virulence of the strains, the acceptability of the diagnostic tests, and knowledge of the risk factors for infection, despite a possible lower eradication rate and higher rate of side effects, a strong argument can be made to proactively screen for and treat H.pylori infection among groups of people with intellectual disability who have a history of institutionalisation, greater levels of intellectual disability or maladaptive behaviour, or live with flatmates with hypersalivation or faecal incontinence.