The second study of infectious intestinal disease (IID2): increased rates of recurrent diarrhoea in individuals aged 65 years and above.

Background: Infectious intestinal disease (IID) is a major health and economic burden in high-income countries. In the UK, there are an estimated 17 million IID cases annually, of which 6 million are caused by the 12 most common pathogens. Host factors that influence risk of IID are not well understood.
Methods: We analyzed data from the IID2 Study, a UK cohort that measured IID incidence, to investigate factors associated with recurrent IID. We calculated rates of IID by age group, sex, previous episodes experienced, and socioecomic indicators. We used Cox models to investigate factors associated with recurrent illness.
Results: The rate of IID was five times higher among infants than those aged 65 years and above (hazard ratio, HR = 5.0, 95% CI: 3.1 - 8.0). However, the association between previous IID and a subsequent IID episode was stronger in the elderly. Among those aged 65 years and above, each additional IID episode increased the rate of subsequent IID three-fold (HR = 3.1, 95% CI: 2.5 - 3.7). Among infants, the corresponding increase was 1.7-fold (HR = 1.7, 95% CI: 1.3 - 2.3).
Conclusions: Elderly populations have a high propensity for recurrent IID. More detailed studies are needed to identify vulnerable subgroups and susceptibility factors, and inform adequate control policies among the elderly.