DIARRHEA CAUSED BYESCHERICHIA COLI

Six major categories of Escherichia coli strains cause diarrhea:1. enterohemorrhagic2. Enterotoxigenic3. Enteroinvasive4. enteropathogenic5. Enteroaggregative6. diffuse-adherent.

• Each has a different pathogenesis, possesses distinct virulence properties,and comprises a separate set of O:H serotypes. Different clinical syndromes and epidemiological patterns may also be seen.

DIARRHEA CAUSED BYENTEROHEMORRHAGIC STRAINS

• This category of diarrhea-causing E. coli was recognized in 1982 when an outbreak of hemorrhagic colitis occurred in the USA and was shown to be due to an unusual serotype, E. coli O157:H7, not previously incriminated as an enteric pathogen.

• The diarrhea may range from mild and non bloody to stools that are virtually all blood.

• Lack of fever in most patients can help to differentiate this infection from that due to other enteric pathogens. The most severe clinical manifestation of EHEC infection is the hemolytic uraemic syndrome (HUS).

• O157:H7, can be identified in stool cultures on sorbitol-MacConkey media by their inability to ferment sorbitol.

Shiga toxin assay• Detection of Shiga Toxin-Producing E.

coli O157 in Human Stool Specimens and Culture.

Reservoir Cattle are the most important reservoir of EHEC; humans may also serve

as a reservoir for person-to-person transmission.

Mode of transmission Mainly through ingestion of food contaminated with ruminant feces. and

unpasteurized dairy milk. Direct person-to-person transmission occurs in families, child care centers . Waterborne transmission occurs both from contaminated drinking water and from recreational waters.

Incubation periodRelatively long, 2–10 days, with a median of 3–4 days.

Period of communicabilityThe duration of excretion of the pathogen is typically 1 week or less

in adults but 3 weeks in one-third of children. Prolonged carriage is uncommon.

SusceptibilityThe infectious dose is very low. Little is known about differences in

susceptibility and immunity, but infections occur in persons of all ages. Children under 5 years old are most frequently diagnosed with infection and are at greatest risk of developing HUS. The elderly also appear to be at increased risk of complications.

DIARRHEA CAUSED BYENTEROTOXIGENIC STRAINS

• A major cause of travellers’ diarrhea in people from industrialized countries who visit developing countries.

• this disease is also an important cause of dehydrating diarrhea in infants and children in the latter countries.

• Enterotoxigenic strains may behave like Vibrio cholerae in producing a profuse watery diarrhea without blood or mucus. Abdominal cramping, vomiting, acidosis and dehydration can occur; low grade fever may or may not be present.

• symptoms usually last less than 5 days.

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• ETEC can be identified through demonstration of enterotoxin production, immunoassays, bioassays or DNA probe techniques .

• None of these assays are widely available in clinical laboratories, and ETEC infections are almost certainly underdiagnosed.

ReservoirHumans. ETEC infections are largely species-specific; people

constitute the reservoir for strains causing diarrhea in humans.

Mode of transmission• Contaminated food and, less often, contaminated water.

Transmission via contaminated weaning foods may be particularly important in infection of infants.

Incubation periodIncubations as short as 10-12 hours have been observed in outbreaks

DIARRHEA CAUSED BYENTEROINVASIVE STRAINS

• This inflammatory disease of the gut mucosa and submucosa caused by EIEC strains of E. coli closely resembles that produced by Shigella.

• The organisms possess the same plasmid-dependent ability to invade and multiply within epithelial cells.

• Clinically, the syndrome of watery diarrhea due to EIEC is much more common than dysentery. The O antigens of EIEC may cross-react with Shigella O antigens.

• Illness begins with severe abdominal cramps, malaise, watery stools, tenesmus and fever; in less than 10% of patients, it progresses to the passage of multiple, scanty, fluid stools containing blood and mucus.

Occurrence EIEC infections are endemic in developing countries, and cause

about 1%–5% of diarrheal episodes among people visiting treatment centers. Rarely, infections and outbreaks of EIEC diarrhea have been reported in industrialized countries.

Mode of transmissionThe scant available evidence suggests that EIEC is transmitted by

contaminated food

DIARRHEA CAUSED BYENTEROPATHOGENIC STRAINS

• The oldest recognized category of diarrhea-producing E. coli, implicated in 1940s and 1950s studies in which certain O:H serotypes were found to be associated with infant summer diarrhea, outbreaks of diarrhea in infant nurseries, and community epidemics of infant diarrhea.

• Diarrheal disease in this category is virtually confined to children under 1 in whom it causes watery diarrhea with mucus, fever and

dehydration.

• EPEC cause dissolution of the microvilli of enterocytes and initiate attachment of the bacteria to enterocytes. The diarrhea in infants can be both severe and prolonged, and in developing countries may be associated with high case fatality.

Occurrence• Since the late 1960s, EPEC has largely disappeared as an important

cause of infant diarrhea in North America and Europe.• However, it remains a major agent of infant diarrhea in many

developing areas, including South America, southern Africa and Asia.

Reservoir—Humans.

Mode of transmissionThrough contaminated infant formula and weaning foods. In infant

nurseries, transmission by fomites and by contaminated hands can occur if handwashing techniques are compromised.

DIARRHEA CAUSED BYENTEROAGGREGATIVE E. COLI

This category of diarrhea-producing E. coli was first associated with infant diarrhea in a study in Chile in the late 1980s.

Infectious agent• EAggEC harbour a virulence plasmid required for expression

of the unique fimbriae that encode aggregative adherence and many strains express a cytotoxin/enterotoxin.

• Among the most common EAggEC O serotypes are O3:H2 and O44:H18.

DIARRHEA CAUSED BYDIFFUSE-ADHERENCE E. COLI

• DAEC is the least well-defined category of diarrhea-causing E. coli

• Data from several epidemiological field studies of child diarrhea in developing countries have found DAEC to be significantly more common in children with diarrhea than in matched controls.

• Preliminary evidence suggests that DAEC may be more• pathogenic in children of preschool age than in infants and

toddlers

Methods of control1. Manage slaughterhouse operations to minimize

contamination of meat by animal intestinal contents.

2.Pasteurize milk and dairy products. Irradiate beef, especially ground beef.

3. Decrease the carriage and excretion of E. coli O157:H7 in cattle on farms, and especially in the days just before slaughter. .

4. Wash fruits and vegetables carefully, particularly if eaten raw.

5.Wash hands thoroughly and frequently after contact with farm animals or the farm environment.

6. Heat beef adequately during cooking, especially ground beef, preferably to an internal temperature of 68°C (155°F) for at least 1516 seconds.

Epidemic measures• If a waterborne outbreak is suspected, issue an order to boil

water and chlorinate suspected water supplies adequately under competent supervision or do not use them.

• If a swimming-associated outbreak is suspected, close pools or beaches until chlorinated or shown to be free of fecal contamination and until adequate toilet facilities are provided to prevent further contamination of water by bathers.

• If a milk borne outbreak is suspected, pasteurize or boil the milk