Infectious Diarrhoea - Part 2 Flashcards
How is a routine bacterial culture used for Bacterial Gastroenteritis?
- difficult to find pathogen in the midst of complex normal flora
- selective and enrichment methods of culture necessary - variety of media and incubation conditions
- takes 3 days to complete all tests
How is Routine Bacterial Culture Campylobacter done?
- specialised culture conditions
- C. jejuni/ C. coli
Very particular culture conditions
Like body temperature and above which is higher than most other bacteria
Likes lower oxygen levels
Routine Bacterial Culture - Campylobacter
is it common?
commonest cause of bacterial food poisoning in UK
Routine Bacterial Culture - Campylobacter
what causes it?
chickens, contaminated milk, puppies
isolated cases rather than outbreaks
Routine Bacterial Culture - Salmonella
how many types is there?
- 2 species recognized: Salmonella enterica, Salmonella bongori
- thousands (!) of serotypes with individual names
- traditionally named after place of first isolation
Routine Bacterial Culture - Salmonella
how is it tested for?
Isolation in the laboratory
screened out as lactose non-fermenters (E. coli ferments lactose and salmonella doesn’t ferment lactose)
serotyping antigen and biochemical tests
Routine Bacterial Culture
Common Salmonella Infections in UK
what are the commonest isolates and where do they come from?
- Commonest isolates are Salmonella enteritidis and Salmonella typhimurium
- > 50% of these imported from abroad
- N.B. - S. typhi and S. paratyphi cause enteric fever (typhoid and paratyphoid) and not gastro-enteritis
what are some other bacteri that may be the cause?
- Shigella (4 species) - outbreaks of Shigella sonnei in nurseries
- E.coli - part of normal gut flora, most strains non pathogenic - several forms of E. coli cause diarrhoea
- enterohaemorrhagic
- enterotoxic (traveller’s diarrhoea)
- enteroinvasive
- enteropathogenic
• routine diagnosis of these E. coli strains not possible - only O157 is easily distinguished from “ordinary” E. coli
What are some other occasional causes of food poisoning outbreaks?
- Staph aureus (toxin)
- Bacillus cereus (re-fried rice)
- Clostridium perfringens (toxin)
Clostridioides (formerly Clostridium) difficile diarrhoea - how do patient usually present?
Patient usually gives history of previous antibiotic treatment – the “4 C antibiotics”
Severity ranges from mild diarrhoea to severe colitis
what are the 2 different toxins that C. diff produces?
C. Diff produces enterotoxin (A) and cytotoxin (B) (inflammatory)
Tox B is the major driver of inflammation
what is the treatment of C. diff
- Metronidazole
- oral vancomycin - Can use oral vancomycin to treat, vancomycin isn’t usually given orally as it is minimally absorbed into the systemic circulation
- Fidaxomicin
- Stool transplants
- surgery may be required - Surgery may be required if extremely severe
Pseudomembranous colitis
Pseudomembranous colitis refers to swelling or inflammation of the large intestine (colon) due to an overgrowth of Clostridioides difficile (C difficile) bacteria. This infection is a common cause of diarrhea after antibiotic use
Mucosal surface of the gut
Inflammation over the mucosa
what is the prevention of CDI?
- Reduction in broad spectrum antibiotic prescribing
- Avoid 4 Cs – cephalosporins, co-amoxiclav, clindamycin, ciprofloxacin
- Antimicrobial Management Team (AMT) and local antibiotic policy
- Isolate symptomatic patients
- Wash hands between patients
what is the management of CDI?
- Stop precipitating antibiotic (if possible)
- Follow published treatment algorithm – oral metronidazole if no severity markers
- raised temp > 38.5
- WCC >15
- acute rising creatinine
- suspicion of colitis/ileus/toxic megacolon
• Oral vancomycin if 2 or more severity markers
what are different kinds of parasites?
• Protozoa and helminths
One cell animal – protozoa
Helminths – worm, can be seen by naked eye
how od you diagnose a parasite?
- Diagnosis generally by microscopy
- Send stool with request “parasites, cysts and ova please” or P, C and O
If suspect parasite then look at stool sample under microscope
Giardia lamblia (aka G. duodenalis/intestinalis) - protozoa
this is a uk parasite, what does it cause?
- Giardiasis - abdominal cramps, bloating, nausea and bouts of watery diarrhoea, malabsorption and failure to thrive
- exist in two forms: cysts, trophozoites
- Cysts - intermittent on stool microscopy; trophozoites - diarrhoea specimen, duodenal biopsy or “string test” (gelatin capsule on absorbent string - swallowed and withdrawn)
Giardia lamblia (aka G. duodenalis/intestinalis) - protozoa
this is a uk parasite, how do you get it?
• contaminated water (ingestion)
Giardia lamblia (aka G. duodenalis/intestinalis) - protozoa
this is a uk parasite, what is the treatment?
• treat with metronidazole
Cryptosporidium parvum (protozoa) is a uk parasite
what forms is there of it
exist in two forms: oocysts, trophozoites
Cryptosporidium parvum (protozoa) is a uk parasite
what does it cause?
Cryptosporidiosis - watery diarrhoea, nausea and vomiting, abdominal cramps, low grade fever
Cryptosporidium parvum (protozoa) is a uk parasite
how is it caused?
ingestion of oocysts in faecally contaminated water
Cryptosporidium parvum (protozoa) is a uk parasite
what is the investigation and treatment?
- oocysts stool specimen seen on microscopy
- no specific treatment usually required
Just rehydration
Can be difficult to eliminate if the patient is immunosuppressed
what are examples of Imported parasites? their effects and their treatment?
- large range of possibilities
- Entamoeba histolytica
- Protozoa - exist cyst, trophozoite forms
- amoebic dysentery - bloody diarrhoea
- microscopic examination for trophozoites (symptomatic pt) “hot stool”; cysts (asymptomatic patient)
- amoebic liver abscess may be long term complication (“anchovy pus”) – trophozoites multiply in liver cells
- treat with metronidazole (trophozoites); diloxanide furoate (cysts in intestine lumen)
what are the causes of Viral Diarrhoea?
- rotavirus in children under 5 yrs – vaccine UK 2013 8 & 12 weeks (rotavirus cases reduced by aprox 70%)
- common in winter
- certain strains of adenovirus (40/41) also cause diarrhoea
how do you diagnose viral diarrhoea?
• diagnosis of both possible by antigen detection - rapid test
Both can be detected with antigen detection test
• Noroviruses – named after Norwalk, Ohio (first identified)
- Norwalk like viruses
- Winter vomiting disease
what does it cause?
- Diarrhoea and vomiting
- common cause of outbreaks: hospital, community, cruise ships
is norovirus infectious?
- very infectious - infectious dose only 18 virus particles (1g faeces may shed 5 billion infectious doses)
- ward closures common - staff and patients affected
- strict infection control measures needed - alcohol gel not effective measure; isolation
how do you diagnose norovirus?
• diagnosis by PCR
Summary:
- the laboratory investigation of bacterial gastroenteritis: Campylobacter, Salmonella, E.coli
- Parasitic diarrhoea: Giardia, Cryptosporidium, Entamoeba histolytica
- Viral diarrhoea: rotavirus, adenovirus, norovirus
