epidemiology of diarrhea caused by E.coli

1. DIARRHEA CAUSED BY
ESCHERICHIA COLI

2. Six major categories of Escherichia coli strains cause diarrhea:
1. enterohemorrhagic
2. Enterotoxigenic
3. Enteroinvasive
4. enteropathogenic
5. Enteroaggregative
6. 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.

3. DIARRHEA CAUSED BY
ENTEROHEMORRHAGIC 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).

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

5. Shiga toxin assay
• Detection of Shiga Toxin-Producing E.
coli O157 in Human Stool Specimens and
Culture.

6. 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 period
Relatively long, 2–10 days, with a median of 3–4 days.

7. Period of communicability
The 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.
Susceptibility
The 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.

8. DIARRHEA CAUSED BY
ENTEROTOXIGENIC 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.
.

9. • 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.

10. Reservoir
Humans. 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 period
Incubations as short as 10-12 hours have been observed in outbreaks

11. DIARRHEA CAUSED BY
ENTEROINVASIVE 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.

12. 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 transmission
The scant available evidence suggests that EIEC is transmitted by
contaminated food

13. DIARRHEA CAUSED BY
ENTEROPATHOGENIC 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.

14. 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 transmission
Through contaminated infant formula and weaning foods. In infant
nurseries, transmission by fomites and by contaminated hands can
occur if handwashing techniques are compromised.

15. DIARRHEA CAUSED BY
ENTEROAGGREGATIVE 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.

16. DIARRHEA CAUSED BY
DIFFUSE-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

17. Methods of control
1. 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. .

18. 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.

19. 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