Microbiology — Enteric and Diarrhoeal Infections, NMC MBBS licence examination syllabus (Nepal Medical Council).
Enteric and diarrhoeal infections
Everything here travels the same route, and one question sorts most of it.
The infections in this chapter share a transmission route — faecal-oral — which means they share their prevention, and it means an outbreak of any of them is telling you something about water and sanitation rather than about individual bad luck. What separates them clinically is smaller than students expect: mostly whether the stool contains blood, and whether the illness is confined to the gut or has become systemic.
Typhoid is the important exception to the chapter's own title. It is an enteric fever in the sense that it is acquired through the gut, but it presents as a systemic febrile illness in which diarrhoea may be absent altogether — and it is missed for exactly that reason.
🩺 Where this lives: These are diseases of water and sanitation, and they respond to plumbing more than to prescribing. A cholera outbreak is controlled by fixing the water supply, not by stockpiling antibiotics, and handwashing with soap remains one of the cheapest life-saving interventions in existence. That has a clinical corollary worth internalising: a single case of suspected cholera or typhoid is not just a patient to treat but a signal about a community — which is why both are notifiable and why the response is public health as much as clinical.
💡 A note on drugs and numbers. This chapter gives no doses and names no first-line antibiotic. Resistance patterns in enteric fever have changed substantially and differ between regions, so empirical choice must follow current national guidance and local sensitivities — an agent named here would age badly and could mislead. It also gives no incubation periods, which differ between published sources. Childhood diarrhoea, ORS and dehydration assessment are covered in the Childhood Infections chapter.
The question that splits the differential
Watery diarrhoea is secretory — a toxin drives fluid out of an intact mucosa, so there is usually no fever and the volumes can be enormous. Bloody diarrhoea is invasive — the organism damages the mucosa, so there is fever and tenesmus but smaller volumes. That single distinction predicts the likely organisms, the presence of fever, and whether antibiotics are likely to be needed. What it does not change is that rehydration is the treatment in both.
WHY REHYDRATION OUTRANKS EVERYTHING ELSE
In acute diarrhoeal illness, people die of DEHYDRATION and
electrolyte loss — not of the organism itself. Antibiotics
may shorten some illnesses and reduce transmission, but
they do not keep a patient alive who has lost several
litres.
So the order of priorities is always:
1. ASSESS hydration and treat it
2. REPLACE ongoing losses as they occur — this is the
step most often forgotten; a patient can be
rehydrated at 9am and shocked again by noon
3. THEN consider whether an antibiotic is indicated
ANTIMOTILITY DRUGS: avoid in bloody diarrhoea and in
children. Slowing the gut retains the organism and its
toxin, and can precipitate serious complications.
WHEN ANTIBIOTICS ARE MORE LIKELY TO BE INDICATED:
Bloody diarrhoea · systemic illness · suspected enteric
fever · cholera (as an adjunct) · the very young, the
elderly, and the immunocompromised.
Most acute watery diarrhoea in an otherwise well adult
needs fluid and nothing more.
Cholera
💡 Exam angle: cholera questions test whether you reach for fluid or for an antibiotic. The distinguishing features are profuse painless watery stool without fever and a speed of deterioration measured in hours. The answer is aggressive rehydration — intravenous for severe dehydration or shock, oral otherwise — with antibiotics as an adjunct that shortens illness and reduces shedding. And a suspected case triggers notification and action on the water supply.
Typhoid (enteric fever)
Typhoid is the diagnosis most often missed in this group, because clinicians expect a diarrhoeal illness and instead meet a fever without an obvious source. Early on, constipation is as common as diarrhoea. The features worth holding are a fever that climbs over days to weeks rather than spiking abruptly, headache and abdominal discomfort, and relative bradycardia. The test is blood culture, taken before antibiotics — and the Widal test is unreliable enough that a positive result should not be treated as confirmation nor a negative as exclusion.
THE TYPHOID COMPLICATIONS THAT KILL
These characteristically appear in the LATER weeks of
untreated illness, when the patient may already seem to
have been ill for a long time:
INTESTINAL PERFORATION
Sudden severe abdominal pain, then peritonitis and
shock. It occurs in the ulcerated ileum. In a patient
with typhoid, sudden severe abdominal pain is
PERFORATION until proven otherwise, and it is a
surgical emergency — see the acute abdomen chapter.
GASTROINTESTINAL HAEMORRHAGE
From the same ulcerated bowel.
ENCEPHALOPATHY
Confusion and reduced consciousness in severe disease.
RELAPSE can occur after apparently successful treatment.
CHRONIC CARRIAGE is a public health problem rather than a
clinical one: a person, often asymptomatic, continues to
excrete the organism — classically from the gallbladder —
and can sustain transmission for years. Carriers who
handle food matter enormously, which is why occupational
restrictions and follow-up exist.
Dysentery: amoebic and bacillary
💡 Exam angle: the amoebic liver abscess is a favourite because it breaks the expected pattern — fever with right upper quadrant pain and tender hepatomegaly, frequently with no diarrhoea at the time of presentation. Students who have anchored amoebiasis to "bloody diarrhoea" miss it. Ask about dysentery in the preceding weeks or months, and about travel or residence in an endemic area.
Prevention
Clinical reasoning: four presentations
🔍 Case 1 — litres in an hour
PresentationA man presents with hours of profuse watery diarrhoea and vomiting, no fever and no abdominal pain. He is hypotensive with sunken eyes and cold peripheries. Several neighbours are similarly affected. An antibiotic is prescribed and he is asked to wait.
ErrorTreating the organism before the fluid.
ReasoningProfuse painless watery diarrhoea without fever, with rapid progression to shock and a cluster of cases, suggests cholera. Death here is from hypovolaemia, and it can occur within hours.
AnswerImmediate aggressive intravenous rehydration, then replacement of ongoing losses, with antibiotics as an adjunct per national guidance. Notify, and investigate the water supply — the neighbours matter as much as the patient.
🔍 Case 2 — two weeks of fever, no diarrhoea
PresentationA 22-year-old has had fever climbing over twelve days, headache, abdominal discomfort and constipation. His pulse seems slow for the height of his fever. Typhoid is dismissed because he has no diarrhoea.
TrapExpecting an enteric fever to be a diarrhoeal illness.
ReasoningTyphoid is a systemic febrile illness. Constipation is as common as diarrhoea early on, and a stepwise fever with relative bradycardia fits well.
AnswerBlood cultures before antibiotics, then treat per current national guidance and local sensitivities. Do not rely on a Widal test in either direction, and watch for perforation as the illness progresses.
🔍 Case 3 — sudden pain in week three
PresentationA patient being treated for typhoid, three weeks into the illness, develops sudden severe abdominal pain with guarding and rigidity, then becomes shocked. The team attributes the pain to the underlying infection.
Key clueSudden severe pain with peritonism in established typhoid.
ReasoningThis is intestinal perforation of the ulcerated ileum — the classic late complication, and a surgical emergency rather than a feature of the fever.
AnswerResuscitate, involve surgery urgently, and manage as a perforated viscus. Attributing new peritonism to the known diagnosis is exactly how this is missed.
🔍 Case 4 — a tender liver and no diarrhoea
PresentationA man has three weeks of fever, right upper quadrant pain and tender hepatomegaly. He has no diarrhoea now, though he recalls several weeks of intermittent bloody stools some months ago.
Diagnosis to considerAmoebic liver abscess.
ReasoningAmoebiasis can spread from the colon to the liver, and the abscess often presents when the bowel symptoms have long since settled. The absence of current diarrhoea does not argue against it.
AnswerImaging and appropriate investigation, with drug treatment per national guidance; most respond without drainage, which is reserved for selected cases. Ask about past dysentery in any unexplained liver abscess.
Commonly confused
Confusion
The distinction
Why it matters
Watery vs bloody diarrhoea
Secretory versus invasive
Predicts organism, fever and antibiotic need.
Antibiotics vs rehydration
Dehydration is what kills
Fluid comes first in every case.
Rehydrating vs replacing ongoing losses
Losses continue after the first bag
Patients are rehydrated then become shocked again.
Typhoid vs gastroenteritis
Typhoid is systemic; constipation is common
The commonest reason it is missed.
Blood culture vs Widal test
Widal is unreliable both ways
Culture before antibiotics is the test.
Typhoid pain vs perforation
Sudden severe pain with peritonism
A surgical emergency, not the fever.
Bacillary vs amoebic dysentery
Abrupt with high fever versus gradual
Amoebiasis can seed the liver.
Liver abscess vs current diarrhoea
The bowel symptoms may be long past
Absence of diarrhoea does not exclude it.
Rapid revision
MUST-KNOW FACTS
1. All of these infections are FAECAL-ORAL — so prevention is shared.
2. Ask first: IS THERE BLOOD IN THE STOOL?
3. WATERY = secretory, toxin-mediated, intact mucosa, usually no fever.
4. BLOODY = invasive, mucosal damage, fever and tenesmus.
5. REHYDRATION is the treatment in both — dehydration kills.
6. REPLACE ONGOING LOSSES, not just the initial deficit.
7. Avoid ANTIMOTILITY drugs in bloody diarrhoea and in children.
8. Most acute watery diarrhoea in a well adult needs fluid alone.
9. CHOLERA: profuse PAINLESS watery stool, NO fever, "rice-water".
10. Cholera can cause shock within HOURS.
11. Cholera treatment is aggressive REHYDRATION; antibiotics are adjunctive.
12. Suspected cholera is a public health emergency — notify, act on water.
13. TYPHOID is a SYSTEMIC febrile illness, not a diarrhoeal one.
14. CONSTIPATION is as common as diarrhoea early in typhoid.
15. Fever climbs over days to weeks; relative BRADYCARDIA may be present.
16. BLOOD CULTURE is the diagnostic test — take it BEFORE antibiotics.
17. The WIDAL test is unreliable in both directions.
18. Typhoid complications appear in the LATER weeks.
19. INTESTINAL PERFORATION is the feared complication.
20. Sudden severe abdominal pain in typhoid = perforation until excluded.
21. Also gastrointestinal haemorrhage and encephalopathy.
22. Relapse can follow apparently successful treatment.
23. CHRONIC CARRIERS, classically gallbladder, sustain transmission.
24. Food handlers who are carriers matter enormously.
25. BACILLARY dysentery: abrupt onset, high fever, tenesmus, very infectious.
26. AMOEBIC dysentery: gradual onset, less fever, may be intermittent.
27. Amoebiasis can spread to the LIVER.
28. AMOEBIC LIVER ABSCESS: fever, right upper quadrant pain, tender liver.
29. Liver abscess often presents WITHOUT current diarrhoea.
30. Most amoebic liver abscesses respond to drugs; drainage is selective.
31. Prevention: safe WATER, SANITATION, HANDWASHING with soap.
32. Typhoid and cholera vaccines exist — used per national policy.
33. Take antibiotic choice from current national guidance and sensitivities.
💡 Exam angle: three reliable threads. Fluid before antibiotics in any acute diarrhoeal illness. Typhoid presenting as fever without diarrhoea, diagnosed by blood culture rather than Widal. And the two complications that break the expected pattern — perforation in typhoid, and liver abscess in amoebiasis.
Syllabus points
Watery versus bloody diarrhoea
Why rehydration outranks antibiotics
Replacing ongoing losses
When antibiotics are indicated
Cholera and the speed of deterioration
Cholera as a public health emergency
Typhoid as a systemic febrile illness
Blood culture versus the Widal test
Intestinal perforation in typhoid
Chronic carriage and food handlers
Bacillary versus amoebic dysentery
Amoebic liver abscess
Water, sanitation and handwashing
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