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3RD YEAR SYSTEMS: Infection > Infectious diarrhoea > Flashcards

Infectious diarrhoea Flashcards

1
Q

Definition of gastroenteritis

A

Three or more loose stools/day

Accompanying features – abdominal pain, fever, vomiting, blood/mucus in the stool

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2
Q

Definition of Dysentery

A

Large bowel inflammation
(+ a lot of abdominal pain), bloody stools

this is an old term but is still used sometimes

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3
Q

Causes of gastro-enteritis

A

Contamination of foodstuffs - Intensively farmed chicken and campylobacter

Poor storage of produce -
Bacterial proliferation at room temperature

Travel-related infections e.g. Salmonella

Person-to-person spread - norovirus

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4
Q

Which is the most common food-borne pathogen?

A

Campylobacter

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5
Q

Which pathogen causes the most hospital admissions each year?

A

Salmonella

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6
Q

What defences do we have against infections? (4)

A

Hygiene

Stomach acidity

Normal gut flora

Immunity

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7
Q

What are the 2 main presentations of gastroenteritis?

A
  1. Non-inflammatory/secretory gastroenteritis
  2. Inflammatory gastroenteritis

It can also be a mix of the two i.e. C.difficile

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8
Q

How does non-inflammatory gastroenteritis present?

A

Cholera and E.coli produce toxins causing this.

Frequent watery stools – not caused by inflammation. These patients are losing a lot of fluid – rehydration treatment

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9
Q

Mechanism of diarrhoea in cholera

A

Increased cAMP results in loss of Cl from cells along with Na and K

If you lose salt, you lose water with it => Osmotic effect leads to massive loss of water from the gut

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10
Q

How does inflammatory gastroenteritis present?

A

Toxins produced by the pathogens cause damage/destruction to the mucosal layer resulting in abdominal pain and fever (systemic inflammatory response)

Bacterial infection may be present.

Antimicrobials may be appropriate but rehydration alone is often sufficient

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11
Q

How would you assess a suspected gastroenteritis patient?

A

Find out their symptoms and their duration
>2/52 unlikely to be infective gastro-enteritis

Risk of food poisoning - Dietary, contact, travel history

Assess hydration - postural BP, skin turgor, pulse
Infants - sunken frontanelles, eyes or cheeks, dry mouth or tongue and few or no tears

Features of inflammation (SIRS) - fever, raised WCC

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12
Q

Fluid and electrolyte losses can be severe with secretory diarrhoea. What could result?

A

Hyponatraemia due to sodium loss with fluid replacement by hypotonic solutions

Hypokalaemia due to K loss in stool (40-80mmol/l of K in stools)

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13
Q

Investigations for gastroenteritis patient

A

Stool culture +/- molecular or Ag testing (detect toxins)

Blood culture

Renal function

Blood count

Abdominal X-ray/CT if abdomen is distended, tender

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14
Q

What is spurious diarrhoea?

A

Commonly seen in care home patients.

It’s diarrhoea as a result of constipation – fluid that can get beyond the constipated stool. Easy to diagnose if you do a rectal examination

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15
Q

Campylobacter gastroenteritis

A

Up to 7 days incubation so dietary history may be unreliable

Stools negative within 6 weeks - Doesn’t hang around in your bowel

Abdominal pain can be severe

Post-infection sequelae - long term complication of acute infection - such as gastrointestinal disorders, neurological disorders, and joint disorders.

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16
Q

How do scientists in the lab identify specific pathogens within faecal sample etc?

A

Use selective and enrichment methods of culture - variety of media and incubation conditions

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17
Q

Culture conditions suitable for growth of Campylobacter?

A

Very particular culture conditions:

Temperature range 37-42 degrees and much lower O2 levels

18
Q

Salmonella gastroenteritis

A

Symptom onset usually <48 hrs after exposure / consumption

Diarrhoea usually lasts <10 days

Stays around in your gut

Post-infectious irritable bowel is common

19
Q

What can carry salmonella and cause you to be a source of infection for others over a prolonged period?

A

Gallstones - they can shed salmonella unless removed

20
Q

2 common salmonella species?

A

S.enterica

S.bongori

21
Q

2 common species of campylobacter?

A

C. jejuni

C. coli

22
Q

What toxin does E.coli 0157 produce?

A

Shiga toxin

23
Q

What is E.coli 0157?

A

A serotype of E.coli (there are many others but only O157 is easily distinguished from “ordinary” E.coli).

The shiga toxin that it produces causes the problem.

Infection from e.g. contaminated meat or person-to-person spread (low incoulum)

Typical illness characterised by frequent bloody stools, abdominal pain but no significant fever

The toxin can also cause Haemolytic-uraemic syndrome

24
Q

What is Haemolytic-uraemic syndrome?

A

The toxin causes platelets to clump in the blood vessels. RBC squeeze through these clumps and become haemolysed

Results in renal failure, haemolytic anaemia and thrombocytopenia. Treatment supportive – antibiotics NOT indicated as although they destroy the organism, this releases more toxins into the bloodstream.

25
Q

Occasional causes of food poisoning outbreaks

A

Staph aureus (toxin)

Bacillus cereus (re-fried rice)

Clostridium perfringens (undercooked meat/cooked food left out - toxin accumulates in spore formation)

26
Q

The vast majority of patients don’t require antimicrobial treatment as management of gastroenteritis.

However, a small minority do. Which groups are antibiotics indicated for?

A

Immunocompromised patients

Those with severe sepsis or invasive infection

Chronic illness e.g malignancy

27
Q

Summary

A

Gastroenteritis is common + can be diagnosed clinically

Minority of patients are admitted to hospital

Mainstay of treatment = rehydration – oral or IV

Minority of patients require antibiotics

28
Q

What toxins does C.diff produce?

A

enterotoxin and cytotoxin

29
Q

How do you treat C.diff?

A

metronidazole

If severe - Oral vancomycin - usually don’t take vancomycin orally because it is a big molecule and passive diffusion into the systemic circulation is less than 10%. But in this case it is good as it remains within the gut and can act on the c.diff there

Fidaxomicin (new and expensive)

Stool transplants

Surgery may be required

30
Q

How can you identify salmonella in the lab?

A

Using MacConkey agar which contains a pH indicator – turns pink if bacteria are fermenting lactose and producing acid.

If you grow on this agar, salmonella will not show colour change as they are non-fermenters

31
Q

What do S.typhi and S.paratyphi cause?

A

Typhoid and paratyphoid and not gastro-enteritis

32
Q

How can you prevent C.diff infection?

A

Reduction in broad spectrum antibiotic prescribing

Avoid 4 Cs – cephalosporins, co-amoxiclav, clindamycin, ciprofloxacin

Isolate symptomatic patients

Wash hands between patients

33
Q

Management of C.diff

A

Stop precipitating antibiotic (if possible)

Follow published treatment algorithm – oral metronidazole if no severity markers (i.e. fever, WCC >15, acute rising creatinine or suspicion of colitis/toxic megacolon)

Oral vancomycin if 2 or more severity markers

34
Q

Parasites found in the UK (2)

A

Giardia lamblia

Cryptosporidium parvum

35
Q

Parasitic diarrhoea: Giardia lamblia

A

Causes Giardiasis - abdominal cramps, bloating, nausea and bouts of watery diarrhoea, malabsorption and failure to thrive

Source = contaminated water

treat with metronidazole

36
Q

Parasitic diarrhoea: Cryptosporidium parvum (protozoa)

A

Causes Cryptosporidiosis – watery diarrhoea, nausea and vomiting, abdominal cramps, low grade fever

Exist in two forms: oocysts, trophozoites

Source: ingestion of oocysts in faecally contaminated water

No specific treatment

37
Q

Viral diarrhoea types (3)

A

Rotavirus
Adenovirus
Norovirus

38
Q

What age group does Rotavirus typically affect?

A

Children under 5 yrs

39
Q

Norovirus

A

Very infectious – 1g faeces may shed 5 billion infectious doses

Ward closures common – staff and patients affected

Diagnosis by PCR

Alcohol gel is not effective

40
Q

Parasitic diarrhoea: Entamoeba histolytica

A

Imported parasite into the UK

Amoebic liver abscess may be long term complication (“anchovy pus”) – trophozoites multiply in liver cells

41
Q

Which 4 antibiotics should be avoided to prevent c.diff infection?

A

cephalosporins, co-amoxiclav, clindamycin, ciprofloxacin

3RD YEAR SYSTEMS: Infection (14 decks)

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