Describe campylobacter:
- Curved G-ve bacilli
- Large animal reservoir
- Infection transmitted via contaminated food
- Inflammation, ulceration and bleeding in small and large intestine
- Bacteraemia can occur, and campylobacter can farley cause post-infection demyelination syndrome
- Treatment: fluid replacement is sufficient in most cases, clarithromycin in severe disease
Describe salmonella:
Microbiology: G-ve bacilli
Epidemiology: found in animals, only S typhi and paratyphi do not have an animal reservoir
Pathogenesis: Acquired by contaminated food/water (less common), diarrhoea due to invasion of epithelial cells in the distal SI and subsequent inflammation
Treatment: fluid replacement, abs in severe infection
Describe Shigella:
Similar to salmonella
Pathogenesis: organisms attach to and colonise mucosal epithelium of terminal ileum and colon; no systemic invasion
Shigella dysenteriae produces protein exotoxin (Shiga toxin) causing haemolytic uraemia syndrome (HUS)
Treatment: fluid replacement
Describe cholera:
Microbiology: comma shaped G-ve bacilli
Pathogenesis: flagella and mucinase facilitate penetration of intestinal mucous, diarrhoea due to production of exotoxin
Treatment: oral or IV rehydration, tetracyclines may shorted duration of diarrhoea in severe disease
Describe staphylococcus aureus:
Microbiology: G+ve cocci
Pathogenesis: 50% of SA produce enterotoxins, bacteria multiply at room temperature and produce toxins. Infection via contaminated foods
CFs: Incubation 30mins-6hours, profuse vomiting and abdominal cramps
Tx: illness usually self-limiting so FRx
Control: hygienic food prep and refrigerated storage
Describe E. coli:
Microbiology: G+ve bacilli with six different diarrhogenic groups; though three main: EPEC, ETEC, EHEC
EPEC: adheres via pili, then formation of lesion mediated by intimin protein with disruption of microvilli. Incubation is 1-2 days and causes watery diarrhoea with a fever
ETEC: diarrhoea due to action of 1 or 2 plasmid-encoded toxins (heat labile and heat stable). Incubation period of 1-7 days, causes watery diarrhoea with fever
EHEC: attaching and effacing lesion (like EPEC), production of shiga-like toxins: EC,O157:H7. Causes bloody diarrhoea with no fever. and HUS in severe cases
Treatment is adequate rehydration. Abs not indicated and can worsen HUS, anti motility agents not indicated
Describe bacillus cereus:
Micro: aerobic, spore forming G+ve bacilli
Pathogenesis: spores and vegetative cells contaminate wide range of foodstuffs. 2 types of disease-
- emetic (associated with fried rice, after boiling protein enterotoxin produced during sporulation) and,
- diarrhoeal (spores in food survive cooking, germinate and organisms multiply in food
CFs:
- Emetic disease; incubation 30mins-6hours, causes profuse vomiting with abdominal cramps and watery diarrhoea
- Diarrhoeal disease; no vomiting. Neither have fever
Tx: self-limiting disease
Describe clostridium perfingens
Micro: anaerobic, spore-forming, G+ve bacilli
Pathogenesis: spores and vegetative cells in soil and animal gut, organisms contaminate food (often in bulk cooking of meat) and multiply and produce enterotoxin in large intestine
CFs:
- Incubation 6-24 hours
- 12-24 hour duration
- watery diarrhoea and abdominal cramps, no fever and no vomiting
Tx: self-limiting disease, control by rapid chilling/freezing of bulk-cooked foods and thorough re-heating before consumption
Describe clostridium botulinum:
Micro: anaerobic, spore-forming G+ve bacilli
Pathogenesis:
- uncommon in UK, spore and vegetative cells in soil and animal gut produce powerful heat-labile protein neurotoxinF
- food-borne, infant and wound botulism
- forms of entry for toxin with spreads via bloodstream to enter peripheral nerves where they cause neuromuscular blockade at the synapses
CFs:
- paralysis and progressive weakness, involvement of muscles of chest/diaphragm causes respiratory failure
Tx:
- urgent intensive supportive care to address swallowing and breathing
- treatment with antitoxin
Control: Hygienic food preparation, proper cooking
Describe clostridium difficile:
Micro: anaerobic, spore forming G+ve bacilli, spores resistant to heat, drying, disinfection and alcohol. CFs due to production of potent toxins
Pathogenesis:
- spores and vegetative cells in environment
- carried by 3-5% of the community, though up to 30% in hospital
- infection requires disruption of the normal protective gut flora (commonly due to abx)
CFs:
- mild to severe abdominal pain
- severe cases may develop pseudomembranous colitis
- fulminant cases may progress to colonic dilatation and perforation
- relapses are common
Tx:
- stop abx
- oral metronidazole (if not severe), oral vancomycin (if severe or no improvement on metronidazole
- recurrent disease may need fecal transplant
Control: Antimicrobial stewardship. Infection prevention and control methods. Cleansing/disinfection with hypochlorite disinfectants
Describe listeria monocytogenes:
Micro: G+ve coccobacilli
Pathogenesis:
- widespread in environment
- especially affects pregnant, elderly and immunocompromised
- infection associated with contaminated foods, unpasteurised milk and soft cheese, pate, cooked meats, smoked fish and coleslaw
- invasive infection from GIT results in systemic spread via bloodstream
CFs:
- incubation 3 weeks
- duration 1-2 weeks
- initial flu-like illness with or without diarrhoea, majority of cases present with systemic infection (septicaemia, meningitis)
Tx: IV abx (usually ampicillin and gentamicin)
Control: Susceptible groups should avoid high risk foods
Describe h. pylori:
Micro: G-ve spiral shaped bacilli
Pathogenesis:
- faecal-oral or oral-oral spread
- humans only reservoir
- acquired in childhood and lifelong unless treatedP
- pathogenesis involves cytotoxin production and a range of factors to promote adhesion and colonisation
CFs: Infection is asymptomatic unless peptic ulceration develops, gastric cancer risk
Tx: combined treatment with PPI and combination of abx such as clarithro and metronidazole
What viruses cause GI disease and what age groups are most susceptible to them?
- Norovirus and sapovirus (calciviridae family) can affect all ages and healthy individuals but often most serious in young and elderly
- Rotavirus, adenovirus and astrovirus affects mainly children under 2 years, elderly and immunocompromised
Describe norovirus:
Transmission: person-peron, food-borne, water
- Very small infectious dose and very stable, being able to remain viable in environment for a long time
- 24-48 hour incubation period
- Causes vomiting and diarrhoea
- also nausea, abdominal cramps, headache and muscle aches, fever (rare) and dehydration in young and elderly
- Treated with symptomatic therapy (rehydration)
Describe immunity to norovirus:
Immunity developed only lasts 6-14 weeks, may be link between blood group and norovirus infection
Describe rotavirus:
- Double stranded, non enveloped RNA virus with 5 different strains
- Antigenic variation due to 11 strands of RNA
- 1st infection usually severe, but subsequent infections are less severe
- Symptom; water diarrhoea, abdominal pain, vomiting, loss of electrolytes leading to dehydration
- Spread same as norovirus, may be respiratory droplets too
Describe adenovirus:
- Double stranded DNA virus
- 50 serotypes but 40&41 cause gastroenteritis
- Symptoms: fever and watery diarrhoea
- Supportive treatment
Describe astrovirus:
- Single stranded, non enveloped RNA virus
- Causes less severe gastroenteritis than other enteric pathogens
- Infection usually as sporadic cases but can be outbreaks usually in young children
Describe septic arthritis:
- Commonly causesd (G+ve) by staphyloccus aureus or streptococci (S pyogenes or pneumococcus) or (G-ve) e. coli, h. influenzae, n. menigitidis, n. gonorrhoeae
- Presents with single hot joint, loss of movement and pain
- Investigations: blood cultures, joint aspirate, FBVC, CRP, imaging
- Treated with at least 2 weeks of IV abs, often 3 weeks IV and then 3 oral
Describe prosthetic joint infection:
- Common aetiology; staph A, CoNS, strep, G-ve bacilli
- Prosthesis requires fewer bacteria to establish sepsis than soft tissue
- Avascular surface allows survival of bacteria as they are protected from circulating immune defects and most abs
- Cement can also inhibit phagocytosis and lymphocyte/complement function
- Local or haematogenous spread
- CFs; pain, effusion, warm joint, fever and systemic symptoms
Describe treatment of PJIs:
Surgical repair options:
- DAIR (debride, abx, implant repair (before biofilm forms (acute infection)
- Take out infected joint (if infection occurs over 30 days since surgery)
What are the typical and atypical causes of CAP?
Typical: - streptococcus pneumoniae - haemophilus influenzae - mortadella catharralis Atypical: - mycoplasma pneumoniae - legionella pneumoniae - chlamoydophila pneumoniae/psittaci
Describe haemophilius influenzae:
- Often occurs in older people with underlying lung disease
- Vaccination against type B (causes epiglottitis)
- CFs: abrupt onset, characteristic of CAP:
- cough fever, pleuritic chest pain
- dull percussion, coarse crepitations, increased vocal resonance
- Tx: amoxicillin, though risk of beta-lactamase so can also use co-amoxiclav
Describe streptococcus pneumoniae:
RFs: smoking, alcohol, immunosuppression, influenza, airway disease
CFs: characteristic of pneumonia
- cough, fever, pleuritic chest pain
- dull percussion, fever, increased vocal resonance
Treatment: with penicillin, if allergic use macrolides (clarithromycin) or tetracycline (doxycycline)
