Septic arthritis Flashcards
Septic arthritis is a medical emergency. It is a d_____ b_____ infection of a joint
direct bacterial
Which joint is typically affected?
Knee
What 2 things are key presentation signs
Acutely inflamed joint with a fever
What organism most commonly causes septic arthritis?
Staphylococcus aureus
Is staph aureus gram positive or negative?
Positive
Is staph. aureus catalase positive or negative?
Positive
When is a catalase test particularly useful?
When determining whether a gram-positive cocci is a staphylococci or streptococci
Why do some bacteria make catalase?
The enzyme protects bacteria from toxic H2O2 by converting it into water and oxygen
What is seen in a positive catalase test?
There are bubbles in a catalase positive sample due to bubbles of oxygen forming
Is staph. aureus coagulase positive or negative?
Positive
When is the coagulase test used?
To differentiate staphylococcus aureus from s. epidermis and s. saprophyticus which don’t produce coagulase
The enzyme ______ activates fibrinogen in the blood and results in coagulation. This allows staph aureus to “wall” it’s infection off from the host’s protective mechanisms
coagulase
How is the coagulase test carried out?
Add bacteria sample to rabbit plasma. Heat and wait 30 mins.
Any coagulation (cloudy tube) means positive test so is staph aureus.
What other microorganisms commonly cause septic arthritis?
H. influenza (now rare due to immunisation)
Neisseria gonorrhoea
E Coli
Pseudomonas aeruginosa
What are risk factors for septic arthritis?
IVDU
Immunosuppression
Recent surgery
Trauma
Prosthetic joints
Inflammatory joint disease
Diabetes
Osteomyelitis
HIV
What type of bacteria commonly infect prosthetic joints?
Coagulase negative staph. epidermis
How do you diagnose septic arthritis?
Urgent joint aspiration with MC+S and polarised light microscopy
What is the diagnosis if the tests came back sterile and with no crystals?
Reactive arthritis
What is the diagnosis if the tests came back sterile and with positive birefringent rhomboid crystals?
Psuedogout
What is the diagnosis if the tests came back sterile and with positive birefringent needle crystals?
Gout
What would the ESR and CRP levels do in septic arthritis
Rise
If the joint aspirate showed causative organism as n. gonorrhoea, other than immediate management, what else is considered?
Sexual health review
How do you treat septic arthritis?
Joint aspirate to drain
Then empirical antibiotic
What antibiotic is used for gram -ve bacteria like E. coli or p. aeruginosa?
Flucloxacillin
What antibiotic is used for MRSA (staph aureus)?
Vancomycin
What antibiotic is used for gonorrhoea?
IM ceftriaxone and azithromycin
If the patient with septic arthritis is on methotrexate or anti-tnf, what should happen?
They should stop taking these as they are immunosuppressives
If the patient with septic arthritis is on steroids what should happen?
Double the prednisolone dose as there is an increased stress response
What is used for analgesia in septic arthritis?
NSAIDs
