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Microbiology > Infective Endocarditis and Other Cardiac Infections > Flashcards

Infective Endocarditis and Other Cardiac Infections Flashcards

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Biology 101 flashcards
1
Q

What is bacteraemia?

A

AKA septicaemia - this is not a clinical diagnosis (indicates there is a focus of infection elsewhere in the body)

Presence of bacteria in the bloodstream (blood is normally sterile); it is potentially fatal and, if not treated, patient may develop septic shock and die

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2
Q

Blood culture bottles?

A

There are two:
Aerobic
Anaerobic

The fluid is a growth medium and the yellow base indicates a +ve bottle

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3
Q

Why must skin be cleaned before blood culture collection?

A

To prevent contamination of the sample with skin flora

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4
Q

Briefly, how does the blood culture machine work?

A

Incubates cultures for 5 days and detects any CO2 produced that changes the base

Most significant growth occurs within 48-72 hours

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5
Q

Incubation of Staph. aureus?

A

Overnight incubation on different agar plates produces pale gold/white colony of Staph. aureus

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6
Q

Appearance of Strep. viridans colony?

A

Gram +ve cocci in chains

α-haemolysis produces a greenish tinge around the colony

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7
Q

Why are antibiotic discs used?

A

To determine which antibiotics the bacteria is sensitive/resistance to

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8
Q

3 questions to ask oneself with blood culture results?

A
  1. Is this organism in the blood cultures likely to be a skin contaminant?
  2. If not - where (in the patient) is it coming from?
  3. Does the patient need antibiotics and, if so, which antibiotics?
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9
Q

What infections does Strep. pneumoniae cause?

A

Pneumonia

Meningitis

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10
Q

What infections do E. coli, Klebsiella and other coliforms cause?

A

Urinary tract

Gut infections

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11
Q

What infections does Staph. aureus cause?

A

Skin and wound infection
Bone/joint infection
Endocarditis

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12
Q

What is Staph. epidermidis?

A

Commonest “coagulase-negative Staphylococcus”

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13
Q

Infections caused by Staph. epidermidis?

A

Often a skin contaminant, but can infect prosthetic material, e.g: IV line infections and prosthetic heart valve/joints

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14
Q

Cautions with blood cultures?

A

Should take more than one set of blood cultures to confirm

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15
Q

What are the diphtheroids and give an example?

A

Skin contaminants, e.g: Corynebacterium sp.

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16
Q

What is infective endocarditis?

A

Infection of the endothelium of the heart valves that is potentially fatal (often diagnosed late)

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17
Q

Types of infective endocarditis?

A

Acute - present suddenly unwell

Sub-acute - more insidious/gradual onset of symptoms

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18
Q

Predisposing factors to infective endocarditis?

A

Heart valve abnormality:
Calcification/sclerosis in elderly
Congenital heart disease
Post-rheumatic fever (infection with Group A Strep. - neurological damage to heart valves)

Prosthetic heart valve

IV drug users (particulate matter can roughen up valves, part. tricuspid valve, making infection easier)

IV lines

19
Q

Pathogenesis of endocarditis?

A

Heart valve damaged

Turbulent blood flow over roughened endothelium

Platelets/fibrin deposited

Bacteraemia (may be very transient), e.g: from dental treatment

Organisms settle in fibrin/platelet thrombi, becoming a microbial vegetation

20
Q

What are septic emboli?

A

Infected vegetations are friable and break off, becoming lodged in the next capillary bed they encounter, causing haemorrhage or abscesses - potentially fatal

21
Q

Valves commonly infected?

A

Usually left side of heart, i.e: mitral and aortic valves

In drug users (inject into groin), tricuspid valve is often affected

22
Q

Organisms causing endocarditis of native (non-prosthetic) valves?

A

Staph. aureus (most common) - aggressive organism that is a usually the cause of acute endocarditis

Viridans streptococci

Enterococcus sp.

Staphylococcus epidermidis

23
Q

Unusual organisms causing endocarditis?

A

“Atypical” organisms - Bartonella, Coxiella burnetti (Q-fever), Chlamydia, Legionella, Mycoplasma, Brucella

Gram negatives

Fungi

24
Q

Acute endocarditis: presenting symptoms?

A

Overwhelming sepsis and cardiac failure (inference with heart valve function)

25
Q

Subacute presentation: symptoms?

A 
Fever
Malaise
Weight loss
Tiredness
Breathlessness
26
Q

Subacute presentation: signs?

A 
Fever
New/changing heart murmur
Finger clubbing
Splinter haemorrhages
Splenomegaly
Roth spots (retina), Janeway lesions, Osler nodes
Microscopic
27
Q

Why must 3 sets of blood cultures be taken?

A

If all are +ve, this is good evidence of continuing bacteraemia; if only one set if taken and is +ve, it may be a contaminant

Better clinical outcome when causative organism is identified

28
Q

What should be done if blood cultures are negative?

A

Consider serology for “atypical” organisms

Echocardiogram (trans-oesophageal is more sensitive than trans-thoracic)

29
Q

What are early and late prosthetic valve endocarditis?

A

Early - within 60 days and late presentations; usually infected at time of valve insertion and usually due to Staph. epidermidis or Staph. aureus

Late - up to many years after valve insertion (due to co-incidental bacteraemia); wide range of possible organisms

30
Q

Describe endocariditis in IV drug users?

A

Right-sided endocarditis (tricuspid valve)

Usually due to Staph. aureus and often presents as Staph. aureus “pneumonia”, due to embolus going to lungs

31
Q

Why is long-term prognosis in IV drug users poor?

A

Repeated injection

32
Q

Empirical (before results) treatment of infective endocarditis of different types?

A

High-dose, frequent IV antibiotics required

Native valve endocarditis - amoxicillin and gentamicin IV

Prosthetic valve endocarditis - vancomycin, gentamicin IV and rifampicin PO; usually, heart valve replacement is required

Drug user endocarditis - flucloxacillin IV

33
Q

Treatment of infective endocarditis after results show specific organism?

A

IV antibiotics usually given for 4-6 weeks:

Staph. aureus (not MRSA) - flucloxacillin IV

MRSA - vancomycin IV and rifampicin PO

Strep. Viridans - benzylpenicillin and gentamicin IV

Enterococcus sp. - amoxicillin/vancomycin and gentamicin IV

Staph. epidermidis - vancomycin, gentamicin IV and rifampicin PO

34
Q

Monitoring response to therapy?

A

Monitor cardiac function, temp and serum CRP

If failing on antibiotic therapy, consider referral for surgery early

35
Q

Methods of preventing endocarditis?

A

All patients at risk (heart valve lesions, congenital heart disease or prosthetic heart valves):
Require antibiotic prophylaxis when having GI or genitourinary tract procedures, if infection is suspected

36
Q

What is myocarditis?

A

Inflammation of cardiac muscle that is more common in young people (cause of sudden cardiac death)

37
Q

Symptoms of myocarditis?

A

Fever
Chest pain
SoB
Palpitations

38
Q

Signs of myocarditis?

A

Arrhythmias

Cardiac failure

39
Q

Causes of myocarditis?

A

Mainly caused by ENTEROVIRUSES, e.g: Coxsackie A and B, echovirus and influenze, etc

40
Q

Diagnosis of myocarditis?

A

Viral PCR - throat swab and stool for enteroviruses; throat swab for influenze

41
Q

Treatment of myocarditis?

A

Supportive treatment

42
Q

What is pericarditis?

A

Inflammation of the pericardium which can often occur with myocarditis; main feature is chest pain (relieved by sitting up or leaning forward)

43
Q

Causes of pericarditis?

A

Mainly VIRAL aetiology but can be caused by bacteria, e.g: after cardiothoracic surgery; rarely there is secondary spread from endocarditis/pneumonia

44
Q

Treatment of pericarditis?

A

Supportive treatment unless there is a bacterial cause (in which case, antibiotics and drainage are used)

Microbiology (13 decks)

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