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Medical Microbiology > Pyrexia of Unknown Origin & Bloodborne Infections > Flashcards

Pyrexia of Unknown Origin & Bloodborne Infections Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

What is pyrexia?

A

Fever

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2
Q

How is someone diagnosed with pyrexia of unknown origin (PUO)?

A

Investigations into a sick patient with fever
Fever > 38C
No localising signs
Initial investigations are negative for > 3 weeks

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3
Q

What investigations are done for sick patients with fever?

A

Most patients will have resolution without diagnosis
For others - rapid identification of focus and cause e.g. pneumonia, cellulitis

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4
Q

What percentage of PUOs are caused by infections?

A

16%

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5
Q

What percentage of PUOs are caused by malignancies?

A

7%

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6
Q

What percentage of PUOs are caused by inflammatory conditions?

A

22%

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7
Q

What percentage of PUOs have miscellaneous causes?

A

4%

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8
Q

What percentage of PUOs causes remain unknown?

A

50%

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9
Q

What are principal infectious causes of PUO?

A

TB and other mycobacteria
Endocarditis
Osteomyleitis
Deep abscesses - spine, liver, pelvic, retroperitoneal
Brucellosis
Typhoid fever
Malaria

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10
Q

What are principal inflammatory causes of PUO?

A

SLE
Rheumatoid arthritis
Giant cell arthritis and other vasculitis
Sarcoid

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11
Q

What malignancies can cause PUO?

A

Lymphoma
Myeloma
Renal cell carcinoma
Lung cancer

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12
Q

What are some miscellaneous causes of PUO?

A

Factitious fever
Drug fever - inc antibiotics
Genetic e.g. FMF (family Mediterranean fever)

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13
Q

What are some factors that may change the likely causes of PUO?

A

Geography - especially recent travel/migration
Smoking
HIV
Other immunosuppression
Age
Family history
Drug history
Animal contact
Occupation

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14
Q

What is bacteraemia?

A

Bacteria in bloodstream
Not a single disease but an endpoint of different disease processes

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15
Q

How is bacteraemia detected?

A

Blood cultures

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16
Q

What is true bacteraemia often associated with?

A

Illness - fever, hypotension, organ failure, skin features (sepsis, septicaemia, septic shock)

17
Q

What infections can bacteraemia cause?

A

Tissue based infection
Device related infection
Endovascular infection

18
Q

Give examples of tissue based infections

A

UTI
Pneumonia
Peritonitis
Meningitis
Osteomyelitis
Cellulitis
Spinal abscess
Brain abscess

19
Q

Give examples of device related infections

A

Central line
Peripheral cannula
Pacemaker
Vascular graft

20
Q

What is endovascular infection?

A

Endocarditis

21
Q

What does bacteraemia result in?

A

Septicaemia and septic shock - fever, hypotension, multi-organ failure

22
Q

Describe endocarditis

A

Before antibiotics, virtually all patients died
Has many cardiac and non-cardiac features
Central lesion is the cardiac vegetation

23
Q

What are vegetations?

A

Masses composed of fibrin, platelets and infecting organisms, held together by agglutinating antibodies produced by the bacteria
Usually on valves

24
Q

What do vegetations lead to?

A

Valve destruction, perforation
Valve ring abscess
Chordae tendinae rupture
Myocardial abscess with/without pericarditis

25
Q

How are infected vegetations caused?

A

Bacteraemia provide a means of bacteria sticking to the endocardium, causing infected vegetation

26
Q

What are the main causes of bacteraemia in endocarditis?

A

Poor denitation with or without dental procedures - oral Streptococci
Intravenous drug abuse (IVDA)
Intravascular lines - e.g. for dialysis, parenteral nutrition (Staphylococci)

27
Q

How do bacteria stick to the endocardium?

A

Endocardium is damaged
vWF adhered
Platelets adhere
Platelets bind fibrin
Bacteria adhere
More platelets and fibrin laid down, forming a vegetation

28
Q

What leads to a damaged endocardium?

A

Rheumatic heart disease
Congenital heart disease
Degenerative/calcific valves
Prosthetic valves
These all cause turbulence, which leads to a damaged endocardium

29
Q

What are clinical consequences of vegetations?

A

Infected vegetation leads to cardiac murmurs, valve rupture, regurgitation and heart failure
Also causes bacteraemia and features of sepsis -> septic emboli -> lung abscess, brain abscess/stroke, spinal abscess, skin emboli, retinal emboli

30
Q

What is strep endocarditis often associated with?

A

Poor oral hygiene

31
Q

How is endocarditis diagnosed?

A

Blood culture and echocardiography

32
Q

Describe basic principles of treatment of endocarditis

A

If the bug is protected within the vegetation then high dose IV antibiotics, combination, prolonged treatment (3-6 weeks)
If valve damage then surgery
If prosthetic valve then surgery
There is often high operative risk

Medical Microbiology (23 decks)

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