L23 Diarrhoea and Acute Gastro-intestinal illness Flashcards
Define Gastroenteritis, the time frames for acute, persistent and chronic, and two places of origination
Syndrome that has diarrhoea and vomiting
- Acute <14 days
- Persistent 14-30 days
- Chronic 30days +
Two types is
- Nosocomial (hospital)
- Community
What are the natural features of the gut that protect against microbial infection (5) and what are the functions of the gut
Role: absorption of fluid and nutrients
- Gastric acidity protects against
- Intestinal motility can help to move bacteria out
- intestinal microflora help to compete with bad bacteria for growth
Local and systemic immune responses:
- M cells that sample luminal microbes for immune surveillance
- IgA non inflammatory antibodies which provide neutralisation and mucosal protection
Compare and contrast the site, presentation and causes of Non-inflammatory diarrhoea and Inflammatory diarrhoea
NI: Small Bowel
- Caused by enterotoxin/producing organism ingestion, viruses that adhere to mucosa.
- Mucosal disruption that directly affects movement of ions/water without causing acute inflammation/destruction
- Presents: large volume of watery diarrhoea without blood/pus
- May have nausea, vomiting or cramps
ID: Distal Ileum and Colon
- Caused by secretion of cytotoxins, or invasion of intestinal epithelium.
- Acute mucosal inflammation/ ulceration, neuropeptides cause loss of absorptive surface.
- Presents: Blood, mucus and WBC in stool. Pain in lower left quadrant, fever,
Compare the pros and cons of the two methods of diagnosing a pathogen from diarrhoea: Culture and Molecular multiplex PCR.
(microscopy is good for parasites mainly)
- Stool Culture
Cons:
- Labour intensive: Have to differentiate pathogenic bacteria from commensal through selective agar, differential agar and chromogenic agar often require
- Culture is slow: 48-72 hours to grow and identify which isn’t very useful with self limiting acute cases
-Only bacteria is culturable - Syndromic panel molecular testing
Pros:
- Single sample, single test for Viral, bacterial and parasitic pathogens
-Rapid results within an hour
Cons:
- more expensive
- It only detects what primers bind to, so there is potential for missing out pathogens present that are not being tested for
- more sensitive than culture therefore can be difficult to interpret as DNA/RNA can remain positive after resolution/treatment.
- doesn’t have an organism for antibiotic susceptibility testing
How does chromogenic agar work
Targets an organism that grow as coloured colony due to metabolism/hydrolysis of one or more chromogenic enzyme substrate. Or make something that changes pH.
eg. Salmonella produces H2S - black streaks
What is the general management of diarrhoea
- Symptomatic relief
- Rehydration as morbidity/mortality comes from dehydration
- Preventing transmission
- Identifying those at risk of severe disease / disease that requires treatment
- Antibiotics if appropriate: in cases of shiga toxin ecoli and nontyphoid salmonella it doesn’t confirm benefit.
What type of diarrhoea does Food poisoning cause and what is the main pathogens, presentation
Non inflammatory
- Toxin from Staphylococci spp. or B. cereus which are able to multiply at wide range of temperatures
-Rapid onset less than 24hrs usually resolving within 24 hrs. Often at group settings
Describe the pathogenesis of viral gastro-enteritis - what type of diarrhoea and common features
Has a PCR diagnosis.
Non-I diarrhoea.
P: infection of enterocyte epithelium with adherence to mucosa disrupt absorption/secretion
Common features
-Primary malabsorption: viral replication causes necrosis in epithelial cells and loss of carb and protein enzymes.
- Reduces absorptive capacity: Localised responses causing ischaemia of villi and villous atrophy
- Increased motility of Sm I : Autonomic dysfunction
Compare the presentation of Rotavirus vs Norovirus
3rd most common is Enteric adenovirus
N: common and spreads rapidly due to v low infectious dose so needs contact isolation to prevent ward outbreaks which are managed by ward closures.
- vomiting is common feature due to delayed gastric emptying
R: affects almost all children during infancy/early childhood. Severe disease 3mo -2yrs.
- Fever and vomiting followed by diarrhoea.
- Has live attenuated oral vaccine: 6wks , 3 mo.
What is the transmission, presentation, of Shigella spp. bacteria induced inflam diarrhoea
- Human to human transmission- faecal oral, sexual (MSM). Low infectious dose. Can withstand low pH
- Presents with initially watery diarrhoea, fever and abdo pain. Then blood, mucus, pus in diarrhoea.
- Bacteremia is rare bc invasion is superficial above the lamina propria
What is the transmission, presentation, of Campylobacter induced inflam diarrhoea
- Mainly faecal-oral, contaminated food/water (chicken), sometimes human human.
- Causes self limiting inflammatory colitis of J, I and colon. Post infectious complications include Guillan barre syndrome
What is the transmission, time course of incubation Salmonella induced inflam diarrhoea
- 2 types
- Person to person spread or via contaminated food/water. Low infectious dose.
- Long and variable incubation period (1-6 weeks)
What is the transmission, presentation of Giardia induced non-inflam diarrhoea
- Faecal-oral transmission via ingestion of cysts in contaminated food/water. Low infectious dose
- Acute/chronic diarrhoea, abdo pain and malabsorption
- Trophozoites adherence to damages mucosal brush border without invasion reducing absorptive surface
What is the class, action, targeted pathogens, effectiveness as a drug and SE/cautions of using Metronidazole
- Class is Nitroimidazole
- Enters organism via passive diffusion and is activated by electron transport protein found in anaerobes.
Inhibits DNA synthesis and induces DNA damage -> DNA degradation and cell death.
- Targets Anaerobes and some parasites as aerobic bacteria can’t activate it.
- high oral bioavailability, moderate to large volume of distribution, penetrating CNS.
- Well tolerated but has
Nausea, diarrhoea, metallic taste.
- prolonged use can cause irreversible peripheral neuropathy
- have to avoid alcohol for 3 days otherwise vomiting, nausea, flushing, tachycardia and dyspnea.
What are differential diagnoses for infectious diarrhoea
- Intra-abdominal infection/systemic infection
2. Non infectious diarrhoea: IBD, Coeliac disease, new meds, IBS
