Gastrointestinal infections in the immunocompromised host

The Malabsorption Syndrome and Its Causes and Consequences

The indication for a small intestinal biopsy is usually the work-up of malabsorption, a clinicopathologic picture caused by a number of infectious and noninfectious inflammatory conditions. The biopsy is generally taken through an endoscope, by either forceps or suction, from the duodenum or proximal jejunum. Depending upon the underlying condition, morphological abnormalities are seen in malabsorption range from normal mucosa with increased intraepithelial lymphocytes (gluten-sensitive enteropathy, viral gastroenteritis, food allergies, etc.), villous shortening with crypt hyperplasia (celiac disease (CD), treated CD, tropical sprue, and bacterial overgrowth), to completely flat mucosa (CD, refractory sprue, enteropathy-induced T-cell lymphoma, and autoimmune enteropathy). Infectious agents that affect gastrointestinal tract can be grouped as food-borne and water-borne bacteria, opportunistic infections (bacterial, fungal, and viral), viral infections (extremely rarely biopsied), and parasitic and helminthic infections. The majority of these infections are, however, self-limited. Although biopsy is more invasive, the use of this procedure allows detection of other causes, including Whipple's disease, other protozoan forms of diarrhea (e.g., cryptosporidiosis, isosporiasis, or cyclosporiasis), Crohn's disease, or lymphoma that may also present as diarrhea and malabsorption.

Role of upper endoscopy in diagnosing opportunistic infections in human immunodeficiency virus-infected patients

Highly active antiretroviral therapy (HAART) has dramatically decreased opportunistic infections (OIs) in human immunodeficiency virus (HIV)-infected patients. However, gastrointestinal disease continues to account for a high proportion of presenting symptoms in these patients. Gastrointestinal symptoms in treated patients who respond to therapy are more likely to the result of drug-induced complications than OI. Endoscopic evaluation of the gastrointestinal tract remains a cornerstone of diagnosis, especially in patients with advanced immunodeficiency, who are at risk for OI. The peripheral blood CD4 lymphocyte count helps to predict the risk of an OI, with the highest risk seen in HIV-infected patients with low CD4 count (< 200 cells/mm³). This review provides an update of the role of endoscopy in diagnosing OI in the upper gastrointestinal tract in HIV-infected patients in the era of HAART.

Gastroduodenal opportunistic infections and dyspepsia in HIV-infected patients in the era of Highly Active Antiretroviral Therapy

BACKGROUND AND AIM

Dyspeptic symptoms are frequently reported by human immunodefficiency virus (HIV)-infected patients under highly active antiretroviral therapy. Whether opportunistic infections are a cause of dyspepsia is still unknown. In this study we prospectively compare the prevalence of gastrointestinal opportunistic infections in dyspeptic versus non-dyspeptic HIV-infected patients with advanced immunodeficiency.

PATIENTS AND METHODS

Six hundred and ninety HIV-infected patients under highly active antiretroviral therapy underwent esophagogastroduodenoscopy with mucosal biopsies from the stomach and duodenum. Group 1: 500 patients (161 women, 339 men; mean age 38.8 years; mean CD4 count 154.3 cells/mm(3) with dyspeptic symptoms such as epigastric pain, nausea, vomiting and fullness. Group 2: 190 patients (169 men, 21 women; mean age 40.7 years; mean CD4 count 171.6 cell/mm(3)) with no dyspeptic symptoms.

RESULTS

Group 1: Gastrointestinal opportunistic infections were observed in eight (1.6%), and non-opportunistic parasites in two (0.4%), patients. They were: Cytomegalovirus (four patients), Cryptosporidium sp. (two patients), Schistosoma mansoni sp. (one patient), Strongyloides stercoralis (one patient) and Giardia sp. (two patients). In five patients esophagogastroduodenoscopy showed no mucosal lesions. Group 2: Giardia sp. was detected in two patients (1.1%: P = 0.07947).

CONCLUSION

Gastrointestinal opportunistic infections were shown in a small number of HIV-infected patients under highly active antiretroviral therapy with advanced immunodeficiency. Although gastrointestinal opportunistic infections were detected exclusively in the dyspeptic patient group, they could not be related to these symptoms, since the number of infected patients was not statistically significant. To correctly diagnose opportunistic infections, multiple biopsy specimens may be necessary even from normal-appearing mucosa.

Xylose utilization and short-chain fatty acid production by selected components of the intestinal microflora of a rodent pollinator (Aethomys namaquensis)

Namaqua rock mice (Aethomys namaquensis) consume nectar xylose when visiting Protea flowers. Whole-animal metabolism studies suggest that the gastrointestinal microflora plays an important role in xylose metabolism in A. namaquensis. We collected caecal contents under anaerobic conditions, cultured caecal microflora both aerobically and anaerobically, and assessed caecal microbial xylose utilization using a (14)C-xylose incubation assay. All four mice sampled hosted culturable caecal micro-organisms that tested positive for xylose utilization. These were classified by 16S rRNA based taxonomy as: Bacillus subtilis, Bacillus pumilus, Bacillus licheniformis, Shigella boydii, Arthrobacter sp. and members of the fungal genera Aspergillus and Penicillium. Cultures of these isolates were then analyzed by gas chromatography to determine the types and quantities of short-chain fatty acids produced by xylose fermentation. These results are discussed in the context of other studies of gut microflora in vertebrates.

Rifaximin, a poorly absorbed antibiotic: pharmacology and clinical potential

Rifaximin (4-deoxy-4'-methylpyrido[1',2'-1,2]imidazo- [5,4-c]-rifamycin SV) is a synthetic antibiotic designed to modify the parent compound, rifamycin, in order to achieve low gastrointestinal (GI) absorption while retaining good antibacterial activity. Both experimental and clinical pharmacology clearly show that this compound is a nonsystemic antibiotic with a broad spectrum of antibacterial action covering Gram-positive and Gram-negative organisms, both aerobes and anaerobes. Being virtually nonabsorbed, its bioavailability within the GI tract is rather high with intraluminal and fecal drug concentrations that largely exceed the minimal inhibitory concentration values observed in vitro against a wide range of pathogenic organisms. The GI tract represents, therefore, the primary therapeutic target and GI infections the main indication. The appreciation of the pathogenic role of gut bacteria in several organic and functional GI diseases has increasingly broadened its clinical use, which is now extended to hepatic encephalopathy, small intestine bacterial overgrowth, inflammatory bowel disease and colonic diverticular disease. Potential indications include the irritable bowel syndrome and chronic constipation, Clostridium difficile infection and bowel preparation before colorectal surgery. Because of its antibacterial activity against the microorganism and the lack of strains with primary resistance, some preliminary studies have explored the rifaximin potential for Helicobacter pylori eradication. Oral administration of this drug, by getting rid of enteric bacteria, could also be employed to achieve selective bowel decontamination in acute pancreatitis, liver cirrhosis (thus preventing spontaneous bacterial peritonitis) and nonsteroidal anti-inflammatory drug (NSAID) use (lessening in that way NSAID enteropathy). This antibiotic has, therefore, little value outside the enteric area and this will minimize both antimicrobial resistance and systemic adverse events. Indeed, the drug proved to be safe in all patient populations, including young children. Although rifaximin has stood the test of time, it still attracts the attention of both basic scientists and clinicians. As a matter of fact, with the advancement of the knowledge on microbial-gut interactions in health and disease novel indications and new drug regimens are being explored. Besides widening the clinical use, the research on rifaximin is also focused on the synthesis of new derivatives and on the development of original formulations designed to expand the spectrum of its clinical use.