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Emerging Agents Associated with Gastroenteritis
This syndrome shares the same fundamental pathologic lesion as thrombotic, thrombocytopenic purpura. Some authorities believe that HUS/TTP should be considered a single condition. Others believe that HUS should be defined as a disorder marked by microvascular lesions limited to the kidney, while TTP has
| Recent reports have suggested that ampicillin or nalidixic acid |
| treatment of diarrhea due to S. dysentefiae may precipitate the |
| hemolytic uremic syndrome, presumably due release of toxin due to |
| lysis of the organisms duringtreatment. Could this happen with gastroenteritis, diarrhea, diarhea, diarea E. |
| coil induced gastroenteritis? |
C. Etiologic considerations:
1.Pathogenicity associated with the production of several cytotoxins, collectively referred to as verotoxins or Shiga-like toxins (SLTs). Most researchers believe that two of these are most important in2.SLT-1 (Verotoxin I) of £. coil closely resembles the Shiga toxin of Shigella dysenteriae, type 1.
3.SLT-2 (Verotoxin II) is distantly related to shiga toxin.
4.These are protein-synthesis -inhibiting toxins. They cleave adenine residue from rRNA at the site where EF-l-dependent attachment of
5.>60 E. co//serotypes produce SLTs, but O157:H7 predominant pathogen in the EHEC group and most associated with human infections worldwide.
D, Epidemiologic considerations:
1.Most cases associated with contaminated undercooked beef products.2.Raw milk also implicated in outbreaks.
3.Acidic foods. Cider and mayonnaise-based dressings and sauces implicated in 2 different outbreaks.
4.Water. 240 case outbreak in Missouri associated with a municipal water supply. Oregon outbreak among swimmers in a lake. Children's wading pool in Scotland in 1992.
5.Other vehicles: salad, cantaloupe, yogurt, live chickens, dry cured salami
6.There has been a major outbreak of £. coil O157:H7 disease in Japan beginning in 2002. Through 26 August, 2002, 9578 cases had been reported to the WHO, with 11 deaths. Cases are still occurring.
E. Diagnosis:
1.Unlike other E. coil O157:H7 isolates do not ferment sorbitol in 24 hours and are negative in the methyl-umbelliferyl glucuronide assay, which measures glucuronidase activity. Selective media for foods and clinical specimens include sorbitoI-MacConkey agar and cefixime-tellurite sorbitoI-MacConkey agar. Recently, phenotypes that ferment sorbitol have been detected, especially in Europe, and this screening test may2.Antibodies to O157 can be used to identify isolates.
3.PCR assays under development.
A.Enteropathogenic E. coil (EPEC):
1.Long known as cause of diarrhea, particularly in infants in the developing world.
B.Enteroaggregative E. coil (EAEC):
1.First described in 1987.2.Increasingly recognized as causes ofdiarrhea in children and adults, particularly in developing countries.
3.Defined as E. coil that do not secrete heat-labile or heat-stable enterotoxins and adhere to HEp-2 tissue culture cells in an aggregative manner.
4.Adhere, form thick mucus blanket, some exfoliation of enterocytes.
C. Diffusely adherent E. coil (DAEC):
1.Diffusely adhere to HEP-2 tissue culture cells.2.Watery diarrhea without cells or blood.
D.Enteroinvasive E. coil (EIAC):
1.First implicated in human disease by DuPont, et al in 1971.2.Closely related to Shigella.
3.Cause watery diarrhea. Bloody stools seen in a minority of cases.
4.Adults and children. Person to person. Food and water borne.
III. Cyclospora cayetanensis.
A.Background:
1.This organism has received considerable publicity in the lay press in the past 2 years, as well as in communications addressed to3.This is a coccidian parasite. It is an 8-10 micrometer wide sphere that often looks mottled red after modified acid fat staining. There is no animal reservoir for C. Cayetanensis, but other Cyclospora species have been found in rodents, reptiles, and inesctivores.
B.Recent Epidemiology:
1.Some recent widespread epidemics have been linked to raspberries from Guatemala. There have been other raspberry or berry associated outbreaks in which the origin of
2.The organism causes a secretory diarrhea with
3.So far, very few children have been affected. Perhaps that is because outbreaks studied to date have focused on social events, with food, in which participants subsequently suffered from unexpected diarrhea. Perhaps, raspberries, being expensive, are eschewed for children's parties.
4.In untreated patients, symptoms tend to recur. Recommended treatment is
IV.Cryptosporidium parvum.
A.Background:
1.First recognized as a veterinary pathogen early in the 20th century.2.From 1976 until 1982, 7 cases of cryptosporidiosis reported in humans.
3.Since 1982 recognized as a cause of severe, life-threatening diarrhea in AIDS patients.
4.C. parvum is the major human pathogen. Also found in numerous mammals. Recent work tends to differentiate some of the human and animal strains.
5.Cannot be cultivated on artificial media or tissue culture.
C. Epidemiology:
1.Animal to human and human to human, usually via a vehicle, often water. Highly transmissable in a family setting. Zoonotic transmission to humans has been shown, but it is not clear how important this is in the
2.17-32% of nonimmunocompromised persons in Virginia, Texas, and Wisconsin have serologic evidence of infection by young adulthood. More than ¼ of children in rural Anhui, China had serologic evidence of infection by years of age and more than 90% of children lining in an impoverished area of Fortaleza, Brazil,D.Clinical manifestations:
1.Asymptomatic infections can occur in both normal and immunocompromised hosts.
2.In normal hosts, symptomatic illness usually characterized by 3-25 days of diarrhea
3.Immunosuppressed hosts, such as HIV patients, may have chronic, unremitting gastrointestinal symptoms accompanied by dehydration malabsorption, and malnutrition. In HIV patients the organsims may disseminate to extraintestinal sites, particularly the biliary tract. In one study of 82 HIV patients, infected during the cryptosporidiosis epidemic in Milwaukee, 24 patients had biliary tract symptoms. Only 4 (17%) of those 24 patients were alive one year later, compared with 30 (52%) of the 58 without biliary symptoms.
E. Treatment:
1. In the immunocompetent person the disease is self limited. No treatment is necessary.
b.Paromomycin alone or paromomycin with azithromycin will reduce the frequency of stools and the
c Octreotide (Sandostatin) 50-100 micrograms qd subcutaneously or 1 mcg per h IV may be helpful.
d.Nitazoxanide, 1000 mg qd is believed to be helpful by many. However, the seminal clinical trials were