Download Osteo Infections

Microbiology: Bacterial Infections of the Bone and Joint
SEPTIC ARTHRITIS:

Cause: active and overt bacterial infection of the joint
Organisms reach joint by:
o Direct inoculation as a result of trauma
o Migration from a distant focus of infection (rare)

Description:
Most are mono-articular (one joint involved), but can be poly-articular
Mostly knee and ankle joints
Joints are swollen, warm to touch and discolored
Pain occurs all the time (even at rest), but can be worsened by movement

Organisms:
S.aureus most common
Others: H.influenzae, E.coli, Klebsiella spp.
With increase in immunosuppression/aging population: mycobacteria, fungi and various parasites can also be
the cause (infection will appear very much like one caused by S.aureus, but will be much more difficult to treat)
Infection can be mono-microbial (usually) or poly-microbial; depends on origin of bacteria

Pathogenesis:
Once in the joint, organisms multiply in the synovial fluid (great medium to grow in)
Pathogenesis from:
o
Toxins and other molecules produced by the bacterium (induce inflammatory response in the joint)
o Proteolytic enzymes (degrade cartilage and other synovial structures)

Clinical ID:
Blood cultures usually positive for causative organism
Synovial fluid usually shows infecting organism (+ higher leukocyte counts)
Anti-microbial susceptibility testing
Rarely use X-rays or NMR

Treatment:
Anti-inflammatory drugs given to relieve pain
Standard antibiotic treatment often effective
OSTEOMYELITIS:

Cause: active and overt bacterial infection in the head of a growing bone (usually a weight bearing bone)
Organisms reach the bone by blood mediated dissemination from:
o Local site of infection (more common)
o Distant site of infection (rare)

Description:
Disease of young people (in growing bones)
Mono-articular
Usually no visible swelling of the joint or significant discoloration
Joint pain can be severe, especially during active use

Organisms:
S.aureus is the most common
Others: E.coli, Pseudomonas aeruginosa
With increase in immunosuppression/aging population: mycobacteria, fungi and various parasites can also be
the cause
Almost always mono-microbial

Pathogenesis:
Due to toxin and proteolytic enzyme mediated degradation of cartilage OR epiphyseal plate (more serious)

Clinical ID:
Blood cultures usually positive for causative organism
Synovial fluid MAY be culture-positive
Anti-microbial susceptibility testing
X-ray and/or NMR frequently used for diagnosis: prior to invasive sampling of bone

Treatment:
Anti-inflammatory drugs given to relieve pain
Standard antibiotic treatment often effective
REACTIVE ARTHRITIS:

Description:
ACR Definiton: peripheral arthritides frequently accompanied by one or more extra-articular manifestations,
which appear shortly after certain documented infections of the GI or UG systems
Acute or Chronic:
o Acute: manifests within 2-4 weeks of infection
o Chronic: can cycle between active episodes and quiescent phases (remitting-relapsing); ~ ½ ReA
patients develop chronic disease
Joint Symptoms:
o Often asymmetrical (sides of the body affected differently)
o Additive and oligoarticular (joints of lower limbs most often affected)
o Joints are swollen, warm, and tender to touch
o Joints are ALWAYS painful (active and at rest)
Extra-Articular Manifestations:
o Diverse and confusing
o Include: keratoderma blennorrhagicum, thickened or opacified nails, anterior uveitis (swelling of
middle layer of eye), conjunctivitis

Organisms: organisms disseminate to joints via monocytes from primary site of infection
UG Infections:
o C.trachometis
o N. gonorrhoeae
GI Infections: several species (Yersinia, Klebsiella, Campylobacter, Shigella, Samonella)
Respiratory Pathogen: Chlamydia pneumoniae

Pathogenesis:
PATHOGENESIS IS NOT CAUSED BY ACTIVE INFECTION
C.tracheometis and pnemoniae:
o Bacteria reach the joint from UG/respiratory infection
o Bacteria are viable and metabolically active when they reach the joint, but are persistent (not active)
o More likely to cause chronic disease, in which organisms can persist for life
Salmonella (and other GI organisms):
o Bacteria are NOT VIABLE once they reach the joint
o Only Ag is present, which causes inflammation
The organisms (Chlamydia) or the Ags from them (Salmonella) induce powerful immunopathology in the joint
o Infiltration of mononuclear cells, plasma cells
o Proinflammatory cytokine release

Clinical ID:
ACR criteria: requires documented previous genital or GI infection, which can lead to cases being missed
o Example: Chlamydia is often asymptomatic in females (used to be though that ReA was a
predominantly male disorder)
Direct fluorescence Ab assay (DFA): usually negative when it is a Chlamydia-associated ReA
o mAb that is used in the lab targets a protein that is produced from a gene that is SHUT OFF during
persistent phase
PCR is the standard method to diagnose: confirms the presence of organism DNA in synovial tissue or fluid

Treatment:
DIFFICULT TO TREAT: Anti-inflammatory drugs are the treatment of choice (but not a cure)
Antibiotics do little to treat infection
o Some are specifically contraindicated because they can drive organism into persistent phase
(ciprofloxacin, doxycycline, and others)
o Combination therapy currently in clinical trials (promising)