Diarrhoea in the elderly: epidemiological and aetiological factors

Mechanisms of drug-induced diarrhoea in the elderly

In the rapidly increasing elderly population, diarrhoea as a result of drug therapy is an important consideration. The elderly consume a disproportionately large number of drugs for multiple acute and chronic diseases. Drugs can compromise both immune and nonimmune responses. Aging decreases the quality and proportion of T cells which in turn reduces the production of secretory IgA, the primary immune response of the gut. Acid production in the stomach decreases with increasing age and this compromise its vital 'self-sterilising' function, thus increasing the risk of diarrhoea due to viral, bacterial and protozoal pathogens. Other nonimmune defence mechanisms include the motility of the small intestine and the host-protective commensal bacteria of the colon. Drug induced hypomotility may result in bacterial overgrowth, deconjugation of bile salts and diarrhoea. Less commonly, diarrhoea may occur due to hypermotility because of a cholinergic-like syndrome. In the colon the host-protective commensal bacteria provide a powerful defence against pathogens. Disruption of this commensal population by antibiotic therapy may result in Clostridium difficile supra-infection which causes diarrhoea through toxin production. This is especially important in the elderly patient on chemotherapy for malignancy and those with multiple diseases. The organism responds to vancomycin, metronidazole and bacitracin. Metronidazole is the suggested drug of choice, with vancomycin reserved for relapses. Drugs also cause diarrhoea by interfering with normal physiological processes. Drugs impair fluid absorption by activating adenylate cyclase within the small intestinal enterocyte which increases the level of cyclic AMP. This causes active secretion of Cl- and HCO3-, passive efflux of Na+, K+ and water and inhibition of Na+ and Cl- into the enterocyte. Examples of these drugs (secretagogues) are bisacodyl, misoprostol and chenodeoxycholic acid (used to dissolve cholesterol gallstones). Drugs may also affect a second mechanism that regulates water and electrolyte transport, the Na+, K+ exchange pump. The energy for this pump is provided by the ATPase mediated breakdown of ATP. ATPase may be inhibited by digoxin, auranofin, colchicine and olsalazine. A number of drugs cause osmotic diarrhoea including antacids containing magnesium trisilicate or hydroxide. Lactulose is being used increasingly in compensated liver disease to increase protein tolerance and prevent hepatic encephalopathy. Sorbitol, an osmotic laxative agent also used in some liquid pharmaceutical preparations, induces diarrhoea by virtue of its osmotic potential. Another mechanism by which drugs cause diarrhoea is by mucosal damage of the small and large bowel. In the small intestine mucosal damage causes diarrhoea and fat malabsorption, as may occur with neomycin and colchicine. In the colon, for example, gold salts and penicillamine cause colitis of varying severity. Though the causes of diarrhoea are diverse, a drug-associated aetiology should always be considered and actively sought and addressed to prevent the complications of dehydration, electrolyte imbalance and undernutrition.

Community-based study of the incidence of gastrointestinal diseases in The Netherlands

The incidence of gastrointestinal diseases was studied in a community-based study in four regions of The Netherlands. Two grades of severity were distinguished--1: diarrhoea or vomiting and at least 2 additional symptoms within the period of 1 week, and 2: diarrhoea or vomiting and at least 2 additional symptoms occurring on the same day lasting at least 2 days within the period of 1 week. The incidence of gastrointestinal episodes was calculated to be 630 for grade 1 and 180 for grade 2 disease per 1000 person-years, after correction for age and sex. The incidence was higher for women than for men (relative risk 1.25) and lower for those in the 19-64-year-old age group when compared to those younger or older (relative risk 0.75 and 0.40, respectively). Independent of the degree of severity of the symptoms, about 20% of the patients had consulted a general practitioner, about half in person and half by telephone. It is concluded that community studies are essential to assess the real incidence of gastrointestinal diseases in the population.

Gastrointestinal health effects associated with the consumption of drinking water produced by point-of-use domestic reverse-osmosis filtration units

During a prospective epidemiological study of gastrointestinal health effects associated with the consumption of drinking water produced by reverse-osmosis domestic units, a correlation was demonstrated between the bacterial counts on R2A medium incubated at 35 degrees C and the reported gastrointestinal symptoms in families who used these units. A univariate correlation was found with bacterial counts on R2A medium at 20 degrees C but was confounded by the bacterial counts at 35 degrees C. Other variables, such as family size and amount of water consumed, were not independently explanatory of the rate of illness. These observations raise concerns for the possibility of increased disease associated with certain point-of-use treatment devices for domestic use when high levels of bacterial growth occur.