Small intestinal bacterial overgrowth in the symptomatic elderly.

Objective: 1) To determine the prevalence of small intestinal overgrowth with colonic-type bacteria in symptomatic elderly subjects, particularly those without important "clues" such as clinically apparent predisposition or vitamin B12 deficiency, and 2) to investigate defense mechanisms such as gastric acidity, small intestinal motility, and luminal IgA in this setting.

Methods: Fifty-two symptomatic subjects without vitamin B12 deficiency or clinically apparent predisposition to bacterial overgrowth or disturbed mucosal immunity, including 22 subjects > or = 75 yr old, underwent culture of small intestinal luminal secretions. Indicator paper was used to measure fasting gastric pH. The presence of bacteria of confirmed nonsalivary origin in small intestinal secretions served as an index of small intestinal dysmotility. Small intestinal luminal IgA concentrations were measured by radial immunodiffusion.

Results: Small intestinal overgrowth with colonic-type flora was not present in any subject investigated for dyspepsia, irrespective of age. In subjects with chronic diarrhea, anorexia, or nausea, overgrowth with colonic-type flora (Enterobacteriaceae) was present in 0/12 (0%), 1/10 (10.0%), and 9/14 (64.3%) subjects aged < 50 yr, 50-74 yr, and > or = 75 yr, respectively. Enterobacteriaceae were not concurrently recovered from saliva of any subject > or = 75 yr old with small intestinal overgrowth with these bacteria. Fasting hypochlorhydria was present in only 1/9 (11.1%) such subjects. Luminal IgA concentrations were significantly greater in subjects > or = 75 yr old with bacterial overgrowth than in culture-negative subjects (p < or = 0.003).

Conclusions: Small intestinal overgrowth with colonic-type bacterial should be considered in subjects > or = 75 yr old with chronic diarrhea, anorexia, or nausea, even in the absence of clues such as clinically apparent predisposition or vitamin B12 deficiency. Small intestinal dysmotility, rather than fasting hypochlorhydria or mucosal immunosenescence, probably is responsible for the prevalence of bacterial overgrowth in this group.