Infectious Diseases Flashcards
What is the definition of meningitis?
How is this different to encephalitis?
meningitis is inflammation of the leptomeningeal coverings (pia mater & arachnoid) of the brain
it affects the extremes of age due to impaired immunity
encephalitis involves inflammation of the brain parenchyma
What are the typical causative agents of meningitis?
BACTERIA
- Streptococcus pneumoniae
- Neisseria meningitidis
- Haemophilus influenzae type B
- there are also some viral, fungal, parasitic and non-infectious causes
What are the typical causative agents of encephalitis?
there are infectious and non-infectious causes
it is typically caused by VIRUSES
the main cause is the herpesvirus
What are the typical symptoms associated with meningitis?
- photophobia
- neck stiffness
- headache
- fever
What are the typical symptoms of encephalitis?
- altered state of consciousness
- seizures
- personality changes
- cranial nerve palsies
- speech problems
- motor and sensory deficits
What investigations are performed for meningitis and encephalitis?
Meningitis:
- lumbar puncture is performed to obtain CSF
Encephalitis:
- blood cultures
- neuroimaging via MRI scan
- CSF analysis
What is involved in the initial management of meningitis?
empirical antimicrobial therapy should be started promptly until the causative agent is identified
this involves ceftriaxone / vancomycin
What organisms tend to cause meningitis in neonates?
Which one occurs straight after birth and which one is a delayed infection?
- Group B streptococcus is associated with infection in previous pregnancy and/or extended labour
this infection occurs early on in the life of the infant
- E. coli tends to cause late neonatal infection
- Listeria monocytogenes can also cause meningitis in neonates
What organisms tend to cause meningitis in children & teenagers?
-
Haemophilus influenzae tends to cause meningitis in people who are unvaccinated
- this tends to be someone from a poor country or who’s parents don’t believe in vaccines
- Neisseria meningitides is a gram-negative diplococci that can also be responsible
What organism most commonly causes meningitis in adults and the elderly?
Streptococcus pneumoniae
When does Listeria monocytogenes typically cause meningitis?
- the elderly
- alcoholics
- consuming cheese / unpasteurised milk
- it likes cold environments and grows on refridgerator items
What are the 2 demonstratable signs associated with meningitis?
- Brudzinski’s sign
- Kernig’s sign
What is Brudzinski’s sign?
- severe neck stiffness causes a patient’s hips and knees to flex when the neck is flexed
What is Kernig’s sign?
- Severe stiffness in the hamstrings causes an inability to straighten the leg when the hip is flexed to 90 degrees
What are the signs of infection that are specific to meningitis?
- fever
- tachycardia
- hypotension
-
skin rash - petechiae - think meningococcal septicaemia
- if there is a skin rash, think Neisseria meningitidis
- altered mental state
What 3 investigations are performed for suspected meningitis and why?
Bloods:
- two sets of blood cultures
Imaging:
- CT scan to exclude bleeding & raised intracranial pressure
Lumbar puncture:
- to obtain CSF which is sent for MC&S and Gram staining
When should lumbar puncture be avoided as an investigation for meningitis?
- if there are neurological signs suggesting raised ICP
- if there is a superficial infection over LP site
- coagulopathy
In normal CSF, what is the:
- appearance
- white cell count
- protein
- glucose
- Gram stain
- it has a clear appearance
- it has very low white cell count
- it has normal levels of protein and glucose
- Gram stain is normal
How do the following characteristics of CSF change if there is bacterial infection?
- appearance
- white cell count
- protein
- glucose
- Gram stain
- appearance is turbid
- white cell count is VERY HIGH with many NEUTROPHILS
- protein is massively increased
- glucose is massively decreased
- this is because bacterial infections take up sugar for nutrition, whereas viral infections do not
- Gram stain is positive
How are the following characteristics of CSF changed in viral infections?
- appearance
- white cell count
- protein
- glucose
- the appearance is clear/cloudy
- white cell count is high with lots of LYMPHOCYTES
- protein is slightly raised
- glucose is normal
How are the following characteristics of CSF changed in TB/fungal infection?
- appearance
- white cell count
- protein
- glucose
- the appearance is clear/cloudy
- the white cell count is high with lots of LYMPHOCYTES
- protein is slightly raised
- glucose is slightly decreased
What infection is suspected if someone has a non-blanching rash?
What is the treatment for this?
- Neisseria meningitidis infection is suspected
- if someone has a non-blanching rash OR meningococcal septicaemia, they need to be admitted
- they are given a single dose of IV benzylpenicillin
What is the general treatment for bacterial meningitis?
- IV ceftriaxone (3rd generation cephalosporin)
-
oral corticosteroids are considered as they reduce inflammation of the meninges
- this is dexamethasone usually
- OCS should NOT be given if meningococcal septicaemia is suspected
If you are thinking of treating bacterial meningitis but the patient’s consciousness is affected, what other treatment should be considered and why?
- if consciousness is affected, consider IV aciclovir
- this covers encephalitis, as the most common cause of encephalitis is viral (herpes virus)
What treatment should be given to close contacts of someone with bacterial meningitis?
- prophylaxis should be given to close contacts
- this involves rifampicin or ciprofloxacin
What is the definition of infective endocarditis?
How common is it?
- it is the infection of endocardial structures
- this mainly involves heart valves
- it involves life-threatening inflammation of the endocardium (innermost layer of the heart)
- it is quite uncommon
What are the 4 causative organisms of infective endocarditis?
- Streptococci
- Staphylococci
- Enterococci
- other organisms (HACEK organisms)
- these will have a negative blood culture
What are the risk factors for infective endocarditis?
- having abnormal heart valves
- e.g. congenital
- post-rheumatic
- calcification / degeneration
- prosthetic heart valves
- IV drug use
- turbulent blood flow (e.g. PDA or VSA)
- recent dental work
What is the difference in the way in which streptococci and staphylococci affect the heart valves in infective endocarditis?
-
streptococci need a damaged heart valve in order to attack
- there needs to be abnormal heart valves
- staphylococci doesn’t need damaged valves to infect the heart, but it is harder for them to enter the body
What valve would you expect to be affected if an IVDU gets infective endocarditis?
- you would expect an infection of the first valve that is encountered from their venous system
- this would be the tricuspid valve
- infective endocarditis of the tricuspid valve - think IVDU
What are the symptoms of infective endocarditis?
- fever with sweats / chills / rigors
- malaise
- arthralgia (pain in a joint)
- myalgia (pain in a muscle / group of muscles)
- confusion
What are the signs of infective endocarditis?
- pyrexia
- tachycardia
- signs of anaemia
- finger clubbing
-
new murmur
- frequency mitral > aortic > tricuspid > pulmonary
- splenomegaly
- vasculitic lesions
What are the 3 types of vasculitic lesion associated with infective endocarditis?
-
Osler’s nodes
- these are tender, painful lesions on the fingers and toes
- they are red-purple, slightly raised and often have a pale centre
-
Roth’s spots
- red spots with white or pale centres that are found on the retina
-
Janeway lesions
- these are non-tender, haemorrhagic lesions that occur on the thenar and hypothenar eminences
What mnemonic is used to remember the features of infective endocarditis?
FROM JANE with <3
- F - Fever
- R - Roth spots
- O - Osler nodes
- M - Murmur
- J - Janeway lesions
- A - Anaemia
- N - Nail-bed haemorrhage
- E - Emboli
- occasionally it can present with haematuria (which tends to be microscopic) due to emboli travelling to the kidneys
What are the 6 buzzwords to remember when thinking about infective endocarditis?
- prosthetic valves
- previous / recent dental procedure
- new onset murmur
- vegetation present on Echo
- right heart (this is usually due to IVDU)
- indwelling catheter (another point of introducing infection)
What investigations are conducted for suspected infective endocarditis?
Bloods:
- FBC - showing high neutrophils & normocytic anaemia
- ESR / CRP
- U&Es
- Rheumatoid factor positive
Duke Criteria:
- in order to determine this 3 blood cultures are needed, each 1 hour apart within 24 hours for diagnosis
Urgent Echo
What is needed for the diagnosis of infective endocarditis?
What treatment is given in the meantime?
- 3 blood cultures are needed, each at least 1 hour apart and all need to be taken within 24 hours
- broad spectrum antibiotics are given until sensitivity is reported
What are the possible complications of infective endocarditis?
- congestive heart failure
- valve incompetence
- aneurysm formation
- systemic embolisation
- renal failure
- glomerulonephritis
What is the management for infective endocarditis affecting native valves?
antibiotics are given for 4 - 6 weeks
- for penicillin-sensitive Streptococcus viridans the treatment is benzylpenicillin + gentamicin
- for Staphylococcus aureus, the treatment is flucloxacillin
- if resistant or penicillin-allergic, then vancomycin is given instead
What is the treatment for infective endocarditis in someone with prosthetic valves?
- this is usually caused by Staphylococci
- the treatment is flucloxacillin + rifampicin + gentamicin
- if the patient is allergic to penicillin then vancomycin is given instead of flucloxacillin
What is the definition of gastroenteritis?
acute inflammation of the lining of the GI tract,
manifested by nausea, vomiting, diarrhoea and abdominal discomfort
What are the viral causes of gastroenteritis?
-
rotavirus
- this was the most common cause in children
- they are now vaccinated against it, so it is not as common
- adenovirus
- astrovirus
- calcivirus
What are the bacterial causes of gastroenteritis?
- Campylobacter jejuni
- Escherichia coli (particularly 0157)
- Salmonella
- Shigella
- Vibrio cholerae
- Listeria
- Yersinia enterocolitica
What are the protozoal causes of gastroenteritis?
- Entamoeba histolytica
- Cryptosporidium parvum
- Giardia lamblia
What is dysentry and how is it different from diarrhoea?
- it involves intestinal inflammation that primarily involves the colon
- it involves mild to severe stomach cramps and severe diarrhoea
- the diarrhoea associated with dysentry contains blood
What mnemonic can be used to remember the organisms which cause dysentry?
CHESS
- C - Campylobacter / Clostridium difficile
- H - Haemorrhagic E. coli
- E - Entamoeba histolytica
- S - Shigella
- S - Salmonella
What are the causes of gastroenteritis that present with diarrhoea and not dysentry?
- Campylobacter / Clostridium difficile
- Staphylococcus aureus
- Vibrio cholera
- E. coli
- Bacillus cereus
- Salmonella
What clues might be in the history of someone presenting with diarrhoea due to C. diff or Staph aureus infection?
- C. diff is associated with the use of antibiotics and/or antiperistaltic drugs
- Staph aureus is associated with food
it comes on 1 - 6 hours after eating and is short-lived
What clues might be in the history of someone presenting with diarrhoea due to Vibrio cholera and E. coli?
- Vibrio cholera is associated with rice water diarrhoea, poor sanitation and shock
- E. Coli is associated with consumption of leafy vegetables
What clues might be in the history of someone presenting with diarrhoea due to salmonella or Bacillus cereus?
Salmonella:
- mainly comes from eggs and can also come from poultry
- may present with constipation
- multiplies in Peyer’s patches of the intestine
Bacillus cereus:
- associated with reheated rice
- can cause cerebral abscess
What clues might be in the history of someone presenting with diarrhoea due to haemorrhagic E. coli?
What does this infection cause?
- it is associated with consumption of leafy vegetables
- it is characterised by bloody diarrhoea followed by haemolytic uraemic syndrome
What clues might be in the history of someone presenting with diarrhoea due to Entamoeba histolytica or campylobacter?
- Entamoeba histolytica is associated with poor sanitation, tropical places and MSM
- Campylobacter is associated with uncooked poultry
What clues might be in the history of someone presenting with diarrhoea due to shigella?
- person-to-person contact
- poor sanitation
- MSM
What are the symptoms of gastroenteritis?
- sudden onset nausea
- vomiting
- anorexia
- diarrhoea (+/- blood)
- abdominal pain
- fever and malaise
What signs might be present on examination of someone with gastroenteritis?
- check mucous membranes for signs of dehydration
- assess skin turgor and capillary refill
- measure HR and BP to assess whether patient is in shock
- temperature
What other investigations are carried out for gastroenteritis?
Bloods:
- FBC
- ESR / CRP
- U&Es will be deranged - low potassium in severe D&V
Stool MC&S:
- bacterial pathogens
- ova cysts (eggs)
- parasites
What is the treatment for gastroenteritis when the patient has no systemic signs?
- systemic signs include shock and dehydration
- supportive therapy is given
- bed rest and fluid and electrolyte replacement with oral rehydration solution
- this is given due to loss of nutrients / vitamins through diarrhoea/vomiting
What is the treatment for gastroenteritis when there are signs of systemic illness?
How is systemic illness defined and what investigation is carried out?
- systemic illness is defined as:
- temperature > 39oC or dehydration
- visible blood
- or duration > 2 weeks
- patient is admitted and given oral fluids
- IV rehydration is required for severe vomiting
- antibiotics are given if the infective organism is identified
- a direct faecal smear then culture is obtained
Hepatitis A
- jaundice, RUQ pain and raised ALT & AST are suggestive of hepatitis
- Jamaica is an endemic country and hepatitis A is faeco-orally transmitted
What signs and tests would point towards a diagnosis of hepatocellular carcinoma?
- combination of jaundice, hepatomegaly and weight loss
- when combined with a raised aFP
B - positive nitrites and Gram-negative bacilli
- this is an E. coli infection
- nitrites are specific for E. coli
- this is more common in women after sexual intercourse as their urethra is shorter
