Week 3: Bacteriology of the gut I Flashcards
Definition of diarrhoea
Increase in stool frequency and liquidity compared to the patient’s usual bowel habit
Clinical presentations of diarrhoea can be classified into:
Acute = less than 14 days Persistent = longer than 14 days Chronic = longer than 30 days
Clinically, what are the two types of diarrhoea?
Secretory:
Watery
Usually produced in large volumes
Contains little or no blood or WBCs
Inflammatory:
Bloody
Produced in smaller volumes
Usually has WBCs
The nature of the causative organism in diarrhoea is dependent on which major factors?
Epidemiological risk factors
Patient’s age
Symptoms
Describe Acute Infectious Diarrhoea
AID is usually a self-resolving illness in immunocompetent individuals
Severe illness occurs in infants and the elderly, in immunocomprimised patients, and malnourished patients
Most deaths occurring due to acute infectious diarrhoea occur in children 5 years or younger, in developing countries
What are the important factor in a clinical history of someone presenting with diarrhoea:
Need to find out the duration and frequency of diarrhoea
Need to explore other GIT symptoms: emesis (vomiting), tenesmus (feeling of needing to pass stools/never feeling satisfied after passing stool/difficulty passing stools), cramping, nausea, anorexia.
Presence of fever
Unintended weight loss
Sexual History must be explored
Medication use - including recent Abx therapy
Recent contact with ill persons, travel, or animal contact
Consumption of raw or undercooked poultry or seafood
Immunocomprimised state (want to rule out)
What things should you take note of during the physical examination of a patient presenting with diarrhoea
Should complete a GI examination
Check hydration status: lethargy, postural hypotension, tachycardia, dry skin (e.g. loss of skin turgor - normal fluid tension of the skin), dry eyes, dry mucous membranes, sunken fontanelles (on infant’s skull)
Investigate other symptoms as indicated by symptoms - e.g. rashes, lymphadenopathy
What are some of the major bacterial causes of diarrhoea in humans?
Salmonella sp
Shigella sp
Diarrheagenic Escherichia coli (entero- haemorrhagic, -toxigenic, -pathogenic, -invasive, and -aggregative)
Yersinia Enterocolitica
Salmonella species: Describe the two clinical groups of salmonella
Typhoid Group = common causes of typhoid (enteric) fever.
Salmonella Typhi
Salmonella Paratyphi
Nontyphoid Group = serotypes other than the typhoid group
Describe the epidemiology and transmission of Salmonella sp
Infections are acquired from ingestion of faecal-contaminated food or drink. Salmonella typhi and paratyphi are transferred via person-to-person transmission. Non-typhi salmonella is transferred via animal-to-person.
Contaminated foods: poultry and beef, unpasteurised milk, eggs and fish, fruits, vegetables, baked goods, medicinal preparations can be contaminated as well
Usually large numbers of salmonellae are required to cause disease (10^8). Yet 10-100 infectious organisms can cause disease in infants, elderly and immunocomprimised.
Describe the Non-typhoid salmonella sp infection presentation:
And what are possible complications?
After 8-48 hours, typical presentation:
- Fever
- Colicky abdominal pain (severe tenderness and rebound tenderness)
- Nausea, vomiting (not protracted)
- Loose watery stools
- Symptoms usually resolve within 2-5 days, and recovery is typically uneventful
Possible complications: bacteremia (inpatients with underlying disease), and Reiteri’s syndrome (reactive arthritis, conjunctivitis, urethritis)
Describe the clinical presentation of typhoid fever
List possible complications
(caused by Salmonella typhi and paratyphi)
Low numbers (<10^3) or organisms can cause disease. Some infected persons become chronic carriers (e.g. Typhoid Mary where the bacteria survived in the gall bladder)
Symptoms of typhoid fever typically evolve over 3 weeks:
- Stepwise fever, with temperature-pulse dissociation (elevated fever but with normal pulse) during the 1st week.
- Abdominal pain and rose spots on the trunk in the 2nd week.
- Hepatosplenomegaly with intestinal bleeding in the 3rd week
Possible Complications:
Bacteraemia, Cholangitis, Pneumonia, Endocarditis, and Osteomyelitis
Is salmonella a nationally notifiable disease?
Yes
How is salmonella infection diagnosed?
Not on clinical presentation alone.
Confirmation:
- Isolation of organisms from stool and/or blood cultures using selective media
- MacConkey agar (lactose fermentation)
- Salmonella Shigella (SS) agar - (lactose fermentation/hydrogen sulfide)
- Hektoen enteric (HE) medium
- Xylose-lysine desoxycholate (XLD) agar
Treatment of Salmonella infection
- The possibility of an underlying disease or immunodeficiency state should be considered with every patient with a severe salmonella infection
- Empirical Abx therapy is not recommended for otherwise healthy patients
- Elderly, immunocomprimised and children:
- Azithromycin (ceftriaxone or ciprofloxacin IV if oral therapy not tolerated)
*Always treat cases of typhoid/paratyphoid - and follow up testing to ensure erradication
Which serotypes of Shigella sp are pathogenic to humans?
Which is the most commonly isolated?
Group A: Shigella Dysenteriae
Group B: Shigella Flexneri
Group C: Shigella Boydii
Group D: Shigella Sonnei
Shigella Sonnei (Group D) is the most commonly isolated and typically causes a watery diarrhoea
What is the most commonly isolated Shigella ap serotype, and what disease does it typically cause in humans?
Shigella Sonnei (Group D serotype). Typically causes watery diarrhoea.
What do the Shigella serovars (aside from Shigella Sonnei) typically cause in humans?
Bacillary Dysentery
Dysentery = inflammatory disorder of the intestine - typically the colon.
Symptoms include fever, abdominal cramping and tenesmus, and bloody diarrhoea.
*Abdo cramps, tenesmus and bloody diarrhoea are hallmarks of Shigella infection
Describe the Epidemiology of Shigellosis
Occurs worldwide, but is especially common in countries lacking effective sanitation (developing countries)
Predominantly affects children 10 years and younger
Shigella (‘epidemics’) are common amongst certain populations, such as:
- Mental or Penal Institutions
- Daycare centres
- Nursing homes
- Amongst male-male sex populations
How is Shigella transmitted?
Humans serve as a natural reservoir for Shigella
Generally takes a fecal-oral route
Outbreaks are commonly associated with swimming pools, spas, and fountains (faecal contaminated waters)
Describe the Pathophysiology of Shigella Infections
Shigella is virulent - thus, only 50-100 organisms are sufficient to cause disease
Shigella infections are typically localised to the columnar epithelial cells of the colon (colonic mucosa).
Thus, bowel perforation or invasion of the bloodstream is extremely rare.
The bleeding (in stools) associated with Shigella infection is usually from superficial ulcerations of the mucosa, due to inflammation
Describe the typical clinical presentation of an individual infected with Shigella sp
Shigella can produce variable (milder) disease, or true dysentery.
Variable Presentation:
The usual incubation period is 24-48 hours
Presentation ranges from mild watery diarrhoea with few (if any) constitutional symptoms, to asymptomatic infection
True Dysentery:
True Dysentery is preceded by watery diarrhoea lasting hours to a few days, then:
- Grossly bloody diarrhoea
- Fever, nausea, vomiting, headache, myalgia
- When severe, dehydration and even circulatory collapse can occur*
- Children 2 or under may have associated neurologic manifestations: seizures, lethargy, and frank coma
- In developing countries, Shigella dysenteriae is associated with hemolytic uremic syndrome (a type of haemolytic anaemia with other causes as well)
Is Shigellosis a nationally notifiable disease?
Yes
How is Shigellosis diagnosed?
Shigellosis is considered in every patient presenting with:
- An acute febrile illness, associated with diarrhoea, especially in patients who have dysenteric stools
Definitive diagnosis of shigellosis is made with stool culture, obtained within the first 3 days of the illness
