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Med Micro 2 > Week 11: Bone, Joint, Blood, Nosocomical Infections > Flashcards

Week 11: Bone, Joint, Blood, Nosocomical Infections Flashcards

1
Q

Types of arthritis that are directly or indirectly caused by microorganisms

A

Reactive, viral and septic

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2
Q

Reactive arthritis follows infection with ______.

A

intracellular bacteria

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3
Q

Reactive arthritis characteristics

A
  • Immune mediated
  • More than one joint affected (polyarthritis)
  • Non-suppurative
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4
Q

Reactive arthritis is associated with which gene?

A

HLA-B27

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5
Q

Reactive arthritis is classified as an a) _______ condition that develops in response to b) ________.

A

a) autoimmune

b) cross-reactivity

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6
Q

Reactive arthritis usually related to infection with gram ____ bacteria

A

negative

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7
Q

Clinical manifestations of clinical arthritis

A
  • Nephritis, carditis, cardiac block
  • Osteoitis
  • Skin, nails, mucosa
  • Intestinal inflammation
  • Urethritis, cervicitis, prostatitis, balantitis
  • Uveitis, irisitis, conjunctivitis
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8
Q

Immunological mechanism behind reactive arthritis

A

Following infection with a gram negative organism, antigens present on the surface of the gram negative organism, trigger an antibody-mediated response. These antibodies cross-react with antigens expressed in the tissues in various organs, causing an inflammatory response.

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9
Q

Virus-associated arthritis

A
  • Can precede several different types of infection e.g. Hepatitis B, rubella, Ross river virus (RRV)
  • Immune-mediated
  • Non-supperative, more than one joint involved due to systemic levels of viral antigen in the circulation
  • In the acute early stage of a viral infection, large amounts of viral antigen are present in the circulation. These can deposit in the joints, leading to antibody interactions triggering inflammation. Cross-reaction is possible and may trigger local inflammation.
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10
Q

Septic arthritis

A
  • Acute infection
  • Usually monoarticular (one joint)
  • Purulent
  • Due to bacterial invasion of a joint
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11
Q

How do bacteria get into a joint?

A
  • Haematogenous spread e.g. from a skin lesion in the area leading to bacteria in the bloodstream which can deposit in a joint
  • Contiguous extension e.g. a wound in a neighbouring tissue, those bacteria can invade the joint and cause inflammation
  • Penetrating trauma
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12
Q

Clinical presentation of septic arthritis

A

Fever
Limitation of movement
Usually joint effusion
Most commonly affected joints: knee (most common), hip, ankle, elbow, wrist

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13
Q

Acute haematogenous arthritis

A
  • A type of septic arthritis resulting from bacteraemia
  • Usually in older children and adults
  • S. aureus most common organism
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14
Q

Contiguous arthritis

A
  • A type of septic arthritis resulting from bacteraemia
  • Results from an infection from a neighbouring lesion or wound
  • Usually polymicrobial e.g. S. aureus, S. pyogenes, S. pneumoniae
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15
Q

Diagnosing septic arthritis

A
  • Blood culture: 50% positive
  • Synovial fluid analysis - culture, microscopy from asperate
  • In a joint asperate, WBC count >100,000/microL
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16
Q

Synovial fluid analysis for septic arthritis

A

Appearance should be clear, yellow indicates protein
Cell count (total and differential)
Gram stain, culture
Examination under polarised light for crystals (gout and pseudogout)

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17
Q

Difference between gout and pseudogout

A

Gout: caused by elevated levels of uric acid in the blood, which crystallises and deposits in the joints and tendons causing inflammation and pain. Characterised by needle-shaped crystals of monosodium urate and negatively birefringent

Pseudogout: Joint disease with similar manifestations. Shorter crystals of calcium pyrophosphate and positive birefringent

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18
Q

Which crystal type found in synovial fluid is associated with bacterial sepsis/infection?

A

Haematodin: orange, highly birefringent, rhomboid form intense orange, fern form green

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19
Q

Causes of osteomyelitis

A
  • Chronic contiguous extension of another local infection in neighbouring tissues e.g. cellulitis from S. aureus; child with otitis media (middle ear infection) where infection migrates to mastoid bone. Most common type of osteomyelitis
  • Acute contiguous e.g. joint replacement (prosthetic device infection), root filled teeth, animal bite, puncture wound. 5% of osteomyelitis cases.
  • Acute haematogenous (15% of osteomyelitis cases) - organisms can deposit in the bone marrow from a bloodstream infection, most commonly S. aureus. Children affected more frequently due to long, rapidly growing bones. Can lead to slow blood flow and areas of progressive necrosis due to poor blood supply. Chronic osteomyelitis can lead to sequstra - dead bone tissue formed within a diseased bone. Diagnosis through blood culture (50% positive rate), aspirate, and nuclear scanning to localise
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20
Q

SIRS definition and clinical criteria

A

Systemic Inflammatory Response Syndrome (may or may not be in response to infection).
Two or more of:
• Temperature >38ºC or <36ºC
• Heart rate >90 beats/min
• Respiratory rate >20/min or PaCO2 <32 mm Hg (4.3 kPa)
• White blood cell count >12 000/mm3 or <4000/mm3 or >10% immature bands

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21
Q

Sepsis definition and clinical criteria

A

Life-threatening organ dysfunction.

Criteria: suspected or documented infection and acute increase ≧ 2 SOFA points (proxy measurement for organ dysfunction)

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22
Q

Septic Shock definition and clinical criteria

A

A subset of sepsis, with underlying circulatory and cellular/metabolic abnormalities are profound enough to significantly increase likelihood of death.
Clinical criteria:
- Sepsis
- Vasotherapy needed to elevate MAP ≧ 65 mm Hg and
- Lactate >2 mmol/L (18mg/dL) despite adequate fluid resuscitation

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23
Q

In blood infections, what does the organism ID tell us?

A
  • Probably site e.g. S. pneumoniea (lung), B. fragilis (abdomen)
  • Potential complications - local site or metastatic
  • Severity: Bacteraemic pneumococcal pneumonia doubles mortality, S. aureus 50% 5 year mortality
24
Q

Causes of transient bacteraemia

A

biopsy, toothbrushing

25
Q

Causes of intermittent bacteraemia

A

abscess

26
Q

Causes of persistent/sustained bacteraemia

A

intravascular

27
Q

What is vegetation in endocarditis composed of?

A

Aggregation of fibrin, platelets and microorganisms

28
Q

How does vegetation form on a heart valve?

A

Microorganisms adhere to injured valve surface via deposited fibrin and platelet aggregates

29
Q

Sepsis inflammatory cascade

A
  1. Insult such as anaphylaxis, uncontrolled infection result in the triggering of TLRs by PAMPs (e.g. LPS) or DAMPs (e.g. DNA, heat-shock protein). This results in the activation of innate immune factors (e.g. complement protein systems, coagulation systems, innate immune cells and subsequent release of cytokines). A large amount of immune mediators are released into the circulation which can result in respiratory distress, excretory failure and other organ failure.
30
Q

Sepsis microbial risk factors

A 
Virulence determinants (e.g. LPS, Protein A/PVL (S. aureus), exotoxins – TSST (S. pyogenes)
Immune evasion mechanisms (e.g. capsule (S. pneumoniae), intracellular (L. pneumophila)
31
Q

Treatment and management of sepsis

A
  1. Resuscitation of induced hypoprofusion with 30 mL/kg if IV crystalloid fluid and assessment of haemodynamic status (e.g. cardiac function) to determine septic shock, give vasopressors (i.e. nonepinephrine) to increase MAP
  2. Antimicrobial Therapies (empiric vs targeted therapies): a) Empiric IV antibiotics to be initiated <1 hour of Sepsis/Septic Shock, covering the majority of nosocomial pathogens
    b) Targeted therapies to be employed immediately following microbial ID
32
Q

White cell predominance in bacterial infections

A

Polymorphs

33
Q

White cell predominance in viral infections

A

lymphocytes

34
Q

White cell predominance in TB infections

A

lymphocytes

35
Q

White cell predominance in Cryptococcus infections

A

lymphocytes

36
Q

Protein CSF patterns in bacterial infections

A

High (>1 g/dl)

37
Q

Protein CSF patterns in viral infections

A

normal

38
Q

Protein CSF patterns in TB infections

A

very high (1-10g/dl)

39
Q

Protein CSF patterns in Cryptococcus infections

A

high (~1g/dl)

40
Q

Glucose CSF patterns in bacterial infections

A

low (<0.6 blood)

41
Q

Glucose CSF patterns in viral infections

A

normal

42
Q

Glucose CSF patterns in TB infections

A

very low or 0

43
Q

Glucose CSF patterns in Cryptooccus infections

A

low

44
Q

Staining from CSF in bacterial infections

A

GPC, GNB

45
Q

Staining from CSF in viral infections

A

-ve

46
Q

Staining from CSF in TB infections

A

probably -ve, mycobacterium tuberculosis stains poorly

47
Q

Staining from CSF in Cryptococcus infections

A

India ink stain +ve

48
Q

Most common HAI

A

Urinary tract infections

49
Q

Source of nosocomial respiratory tract infections

A
  • Intubation/mechanical ventilation
  • Patient generally unconscious - no cough reflex
  • Hardware inserted in trachea bypasses normal protective mechanisms in the respiratory tract (mucocilliary escalator and cough reflexes)
50
Q

Nosocomial pocket infection

A

Purulent discharge of the subcutaneous pocket of an implanted intravascular catheter

51
Q

Exit site infection

A

Erythema or induration within 2 cm of the catheter exit site is observed in absence of a concomitant blood-stream infection

52
Q

Most common cause of antibiotic-associated diarrhoea

A

Clostridium difficile

53
Q

Diagnosis of C. difficile

A

Detection of cytotoxin (toxin B)

54
Q

Risk factors for HAI

A

Host factors: extremes of age, underlying disease (non-infectious), infections that suppress immunity (AIDS), medications (cytotoxic drugs, antibiotics), trauma (burns, surgery), length of stay in hospital, complexity of procedure

55
Q

Risk factor for sepsis from UTI

A
  • Male gender >65
  • Infection with Serratia marcescens, other non-infectious disorders of the uninary tract (kidney stones, enlarged prostate)

Med Micro 2 (8 decks)

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