Week 11: Bone, Joint, Blood, Nosocomical Infections Flashcards
Types of arthritis that are directly or indirectly caused by microorganisms
Reactive, viral and septic
Reactive arthritis follows infection with ______.
intracellular bacteria
Reactive arthritis characteristics
- Immune mediated
- More than one joint affected (polyarthritis)
- Non-suppurative
Reactive arthritis is associated with which gene?
HLA-B27
Reactive arthritis is classified as an a) _______ condition that develops in response to b) ________.
a) autoimmune
b) cross-reactivity
Reactive arthritis usually related to infection with gram ____ bacteria
negative
Clinical manifestations of clinical arthritis
- Nephritis, carditis, cardiac block
- Osteoitis
- Skin, nails, mucosa
- Intestinal inflammation
- Urethritis, cervicitis, prostatitis, balantitis
- Uveitis, irisitis, conjunctivitis
Immunological mechanism behind reactive arthritis
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.
Virus-associated arthritis
- 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.
Septic arthritis
- Acute infection
- Usually monoarticular (one joint)
- Purulent
- Due to bacterial invasion of a joint
How do bacteria get into a joint?
- 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
Clinical presentation of septic arthritis
Fever
Limitation of movement
Usually joint effusion
Most commonly affected joints: knee (most common), hip, ankle, elbow, wrist
Acute haematogenous arthritis
- A type of septic arthritis resulting from bacteraemia
- Usually in older children and adults
- S. aureus most common organism
Contiguous arthritis
- 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
Diagnosing septic arthritis
- Blood culture: 50% positive
- Synovial fluid analysis - culture, microscopy from asperate
- In a joint asperate, WBC count >100,000/microL
Synovial fluid analysis for septic arthritis
Appearance should be clear, yellow indicates protein
Cell count (total and differential)
Gram stain, culture
Examination under polarised light for crystals (gout and pseudogout)
Difference between gout and pseudogout
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
Which crystal type found in synovial fluid is associated with bacterial sepsis/infection?
Haematodin: orange, highly birefringent, rhomboid form intense orange, fern form green
Causes of osteomyelitis
- 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
SIRS definition and clinical criteria
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
Sepsis definition and clinical criteria
Life-threatening organ dysfunction.
Criteria: suspected or documented infection and acute increase ≧ 2 SOFA points (proxy measurement for organ dysfunction)
Septic Shock definition and clinical criteria
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
In blood infections, what does the organism ID tell us?
- 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
Causes of transient bacteraemia
biopsy, toothbrushing
