Infectious diarrhoea Flashcards
define diarrhoea
subjective
change fluidity and frequency of stool in relation to normal
define gasto-enteritis
objective - clinical scenario and not dependent on microbiology
3 or more loose stools/day
accompanying features
define dysentery
large bowel inflammation
bloody stools
type 1 bristol stool
separate hard lumps
like nuts
hard to pass
type 2 bristol stool
sausage shaped but lumpy
type 3 bristol stool
like a sausage but with cracks on the surface
type 4 bristol stool
sausage or snake like
smooth and soft
type 5 bristol stool
soft blobs with clear cut edges
type 6 bristol stool
fluffy pieces with ragged edges
mushy
type 7 bristol stool
watery
no solid pieces
entirely liquid
epidemiology of gastroenteritis
contamination of food - intensively farmed chicken and campylobacter
poor storage of produce - bacterial proliferation at room temp
travel related infections e.g. salmonella
person to person spread - norovirus
prevalence of gastroenteritis
25% have infectious intestinal disorder each year
2% vitis GP because of GI infection p/a
>500 000 cases of food poisoning p/a from known pathogens
commonest cause of gastroenteritis
viruses are commonest cause with campylobacter being the commonest bacterial pathogen (280 000 cases p/a)
salmonella is the pathogen that causes the most hospital admissions (2500 p/a)
what food type is most commonly linked with food poisoning
poultry meat
244 000 cases p/a
defences against enteric infection
hygiene and adequate cooking
stomach acidity (reduced with antacids and infection)
normal gut flora (C. difficile diarrhoea when normal gut flora is reduced through abx use)
immunity (HIV and salmonella)
clinical features of diarrhoeal illness
non-inflammatory/secretory - cholera
inflammatory - shigella dysentery
mixed picture - C difficile
non-inflammatory diarrhoeal illness
secretory toxin mediated
frequent watery stools with little abdo pain
rehydration is the mainstay of therapy
examples of non-inflammatory diarrhoeal illness
cholera - increases cAMP levels and Cl secretion
enterotoxigenic E coli (travellers’ diarrhoea)
mechanism of diarrhoea in cholera
increased cAMP –> loss of Cl from cells along with Na and K
osmotic effect leads to massive loss of water from the gut
inflammatory diarrhoeal illness
inflammatory toxin damage and mucosal destruction
pain and fever
antimicrobials may be appropriate but rehydration alone is often sufficient
examples of inflammatory diarrhoeal illness
bacterial infection
amoebic dysentery
assessing a patient with gastro-enteritis
symptoms and their duration - >2/52 unlikely to be infection GE
risk of food poisoning - dietary, contact, travel hx
assess hydration - postural BP, skin turgor, pulse
features of inflammation (SIRS) - fever, raised WCC
features of gastro-enteritis in infants - clinical features of dehydration
sunken eyes and cheeks sunken fontanelle few or no tears dry mouth or tongue decreased skin turgor sunken abdomen
fluid and electrolyte losses
can be severe with secretory diarrhoea
1-7L fluid/day containing 80-100mmol Na
hyponatraemia due to Na loss with fluid replacement by hypotonic solutions
hypokalaemia due to K loss in stool (40-80mmol/L of K in stools)
investigations in a patient with gastroenteritis
stool culture +/- molecular of Ag testing
blood culture
renal function
blood count - neutrophilia, haemolysis (E. Coli O157)
abdo X-ray/CT is abdomen distended/tender
differential diagnoses
inflammatory bowel disease
spurious diarrhoea - 2y to constipation
carcinoma
diarrhoea and fever can occur w/ sepsis outside the gut - lack of abdo pain/tenderness goes against GE, no blood/mucus in stools
treatment of gastroenteritis
oral rehydration w/ salt/sugar solution
IV saline
campylobacter enteritis
up to 7 days incubation - dietary hx may be unreliable
stools -ve within 6wks
abdo pain can be severe
<1% invasive - +ve blood cultures (consider underlying pathology)
post-infection sequelae
post-infection campylobacter sequelae
Guillain Barre syndrome
Reactive arthritis
salmonella gastroenteritis
symptom onset usually <48hrs after exposure
diarrhoea usually lasts <10 days
<5% +ve blood cultures
20% still have +ve stools at 20/52 (asymptomatic but can still pass on infection) - prolonged carriage may be associated w/ gallstones
post-infectious irritable bowel is common
E. coli O157
infection from contaminated meat or person-to-person spread (low inoculum)
typical illness characterised by frequent bloody stools
abdo pain
toxin produced by E. coli O157
Shiga toxin
E. coli O157 stays in the gut but the toxin gets into the blood
toxin can cause haemolytic uraemic syndrome (HUS) - generally in already compromised pts
what is HUS
haemolytic uraemic syndrome
characterised by renal failure, haemolytic anaemia and thrombocytopenia
treatment is supportive - abx NOT indicated (may make it worse by destroying E. coli O157 and releasing more toxin into bloodstream)
how does E. coli O157 lead to HUS
toxin activated platelet activation
micro-angiopathy results
when are antibiotics indicated in gastroenteritis
immunocompromised pts
severe sepsis or invasive infection
chronic illness e.g. malignancy
not indicated for healthy pt w/ non-invasive infection
what abx are used for campylobacter infection
macrolides
e.g. clarithromycin, azithromycin
what abx are used for salmonella infection
many salmonellas are still sensitive to ciprofloxacin
ceftriaxone is used for more resistant salmonellas
routine bacterial culture for bacterial gastroenteritis
difficult to find pathogen alongside complex normal flora
selective and enrichment methods of culture necessary
takes 3 days to complete all tests
routine bacterial culture - campylobacter
specialised culture conditions
C. jejuni/ C. coli - commonest cause of bacterial gastro-enteritis in UK
chickens, contaminated milk, puppies
isolated cases rather than outbreaks
requires higher temperatures and lower oxygen levels to grow
routine bacterial culture - salmonella
Salmonella enterica, salmonella bongori
thousands of serotypes with individual names
isolated in the laboratory - screened out as lactose non-fermenters
serotyping requires further antigen and biochemical tests
commonest salmonella infections in UK
salmonella enteritidis
salmonella typhimurium
>50% of these are imported from abroad
S. typhi and S. paratyphi cause enteric fever (typhoid and paratyphoid) and not gastroenteritis
other causative bacteria
Shigella ( 4 species) - outbreaks of Shigella sonnei in nurseries
E coli - part of normal gut flora, most strains non-pathogenic, several strains cause diarrhoea
which strains of Ecoli cause diarrhoea
enterohaemorrhagic (O157)
enterotoxic (travellers’ diarrhoea)
enteroinvasive
enteropathogenic
routine diagnosis of these E coli strains not possible - only O157 is easily distinguished from “ordinary” E coli
occasional causes of food poisoning outbreaks
Staph aureus (toxin) Bacillus cereus (re-fried rice) Clostridium perfringens (toxin)
C. difficile diarrhoea
Clostridioides difficile
patient usually has hx of prev abx treatment (4c abx)
severity ranges from mild diarrhoea to severe colitis
what toxins does C difficile produce
enterotoxin and cytotoxin
inflammatory
how is C difficile treated
metronidazole
ORAL vancomycin
fidaxomicin
stool transplants
surgery may be required
C difficile infection prevention
reduction in broad spectrum abx prescribing
avoid 4 Cs
antimicrobial management team (AMT) and local abx policy
isolate symptomatic pts
wash hands between pts - soap and water
what are the 4 Cs
cephalosporins
co-amoxiclav
clindamycin
ciprofloxacin
management of C diff infection
stop precipitating abx (if possible)
follow published treatment algorithm - oral metronidazle if no severity markers
oral vancomycin is 2 or more severity markers
what are the severity markers
raised temp >38.5
WCC >15
acute rising creatinine
suspicion of colitis/ileus/toxic megacolon
parasitology
protozoa and helminths
diagnosis generally by microscopy
send stool with request “ parasites, cysts and ova” (P,C and O)
UK parasites
Giardia lamblia
cryptosporidium parvum
Giardiasis
abdominal cramps
bloating
nausea and bouts of watery diarrhoea
malabsorption and failure to thrive
Giardia lamblia
(aka G. duodenalis/intestinalis)
protozoa
contaminated water
exists in 2 forms: cysts, trophozoites
results in giardiasis
Giardia lamblia cysts and trophozoites
cysts - intermittent on stool microscopy
trophozoites - diarrhoea specimen, duodenal biopsy or “string test” - gelatin capsule on absorbent string, swallowed and withdrawn
Giardia lamblia treatment
metrondiazole
cryptosporidium parvum
protozoa
2 forms: oocysts, trophozoites
water treatment relies on filtration
leads to cryptosporidiosis
cryptosporidiosis clinical presentation
watery diarrhoea
N + V
abdominal cramps
low grade fever
cryptosporidiosis transmission
ingestion of oocysts in faecally contaminated water
oocysts stool specimen seen on microscopy
cryptosporidiosis treatment
no specific treatment usually required
imported parasites
entamoeba histolytica
entamoeba histolytica
protozoa - cyst and trophozoite forms
leads to amoebic dysentery
microscopic examination for trophozoites (symptomatic patient) - “hot stools”, cysts (asymptomatic patient)
amoebic liver abscess may be long term complication - anchovy pus, trophozoites multiply in liver cells
treatment for entamoeba histolytica
trophozoites - metronidazole
cysts in intestine lumen - diloxanide furoate
viral diarrhoea causes
rotavirus
adenovirus
norovirus
rotavirus
viral diarrhoea in children <5y/o
vaccine now available in UK at 8 and 12wks
common in winter
adenovirus
certain strains - 40/41
diagnosis of adenovirus and rotavirus
rapid test - antigen detection
norovirus
winter vomiting disease
diarrhoea and vomiting
common cause of outbreaks: hospital, community, cruise ships
very infectious (low infectious dose - 18 virus particles)
ward closures common - staff and pts affected
strict infection control measures needed - alcohol gel not effective, isolation
diagnosis of norovirus
PCR
