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Case 2: Medical Microbiology, image Label the following, image image …
Case 2: Medical Microbiology
Define the following words: Osteomyelitis, Sequestrum, Septic Arthritis and Prosthetic Joint Infections
Osteomyelitis is the infection of the bone, characterized by progressive bone destruction and the formation of Sequestra
Sequestrum is a piece of devitalized bone that has been separated from surrounding bone during the process of necrosis
Septic arthritis is an inflammatory reaction of the joint space caused by an infectious agent
Prosthetic joint infection is an infection involving the joint prosthesis and adjacent tissue
Osteomyelitis
Osteomyelitis is the infection of the bone characterized by the progressive bone destruction and formation of Sequestra
Clinical Features of Osteomyelitis
List the Clinical features of Osteomyelitis
Fever (present in only 505 of neonates)
Edema
Warmth
Fluctuance
Tenderness on palpation
Reduction in the use of extremity
Failure of young child to sit up normally
Sinus tract drainage (usually a late finding or one that occurs in chronic osteomyelitis)
Complications of Osteomyelitis
List the Complications of Osteomyelitis
Bone Abscess
Paravertebral or Epidural Abscess
Bacteremia
Loosening of prosthetic implant
Overlying soft tissue cellulitis
Drainage of soft tissue sinus tracts
Pathophysiology: Clinical Features of Osteomyelitis
List the Risk factors by Mechanisms of Infection
Contiguous Spread
Contiguous spread occurs by localized/ adjacent structures
May be Polymicrobial or Monomicrobial
Hematogenous Spread
Hematogenous spread is monomicrobial
Direct Trauma/ Surgical Inoculation
Foreign Body/ Prosthesis
Pathophysiology of Osteomyelitis
Describe the Pathophysiology of Osteomyelitis
Bone is normally resistant to infection
However, when microorganism are introduced into the bone Haematogenously from surrounding tissue or from direct inoculation related to surgery, trauma. Osteomyelitis can occur
Bone infection may result from treatment of trauma, which allows pathogens to enter the bone and proliferate in the traumatized tissue
When bone infection persists for months, the resulting infection is known as Chronic Osteomyelitis and may Polymicrobial
Although, all bone are subject to infection, the lower extremity is most commonly involved.
List important factors in the pathogenesis of Osteomyelitis
Virulence of the infecting organism
Underlying disease
Immune status
Type, Location of Vascularity of the bone
Hematogenous Osteomyelitis
Describe Hematogenous Osteomyelitis
In adults, the vertebrae is the most common site of Hematogenous Osteomyelitis
BUT infection may occur in the long bone, pelvis and clavicle
Primary Hematogenous osteomyelitis is more common in infants and children, usually occurring in the long bone metaphysis
However, it can spread to the medullary canal or into the joint
When infection extends into the soft tissues, sinus tracts eventually form.
Contiguous-focus and Posttraumatic Osteomyelitis
Describe Contiguous and Posttraumatic Osteomyelitis
The initiating factor in Contiguous-Focus Osteomyelitis often consists of direct inoculation of bacteria via trauma, surgical reduction and internal fixation of fractures, prosthetic devices , spread from soft tissue infection
Infection usually results 1 month after inoculation
Septic arthritis may lead to osteomyelitis
Abnormalities at the joint margins or centrally which may arise from overgrowth and hypertrophy of synovial pannus and granulation tissue may eventually extend into the underlying bone, leading to erosions and osteomyelitis
Aetiology: Causes of Osteomyelitis
List the organisms that cause Osteomyelitis in All types, Infants, Older kids, Sickle cell disease, Prosthetic Joint infection, Nosocomial Infections, Vertebral Osteomyelitis and IVDU
All Types
Staphylococcus aureus (the most common)
Infants
Staphylococcus aureus, Escherichia coli
Older Kids
Staphylococcus aureus, Streptococcus pneumoniae
Sickle Cell disease
S. aureus
Streptococcus pneumoniae
Prosthetic Joint Infection
Coagulase negative Staphylococci
Nosocomial Infection
Pseudomonas aeruginosa
Vertebral Osteomyelitis
Pseudomonas aeruginosa
Staphylococcus aureus
IVD Users
Staphylococcus aureus
Pseudomonas aeruginosa
Septic Arthritis
Septic arthritis is the inflammatory reaction of the joint space caused by an infective agent
Septic Arthritis: Clinical Features
Most common involved joint in Septic Arthritis is the Knee Joint (50% Cases)
It is followed by the Hip, Shoulder, Ankle and Wrist Joints
List the Clinical Features of Septic Arthritis
Erythema
Swelling
Warmth
Tenderness
Infected joints exhibit an obvious effusion and decreased range of motion
Pathophysiology: Septic Arthritis risk factors by mechanisms of infection
Hematogenous Spread
IV Drug use
Indwelling catheters
Endocarditis
Pre-existing arthritis or joint disease
Rheumatoid arthritis
Osteoarthritis
Direct Inoculation
Trauma
Joint surgery/Injection
Animal bite
Contiguous Spread
Bony infection
Soft tissue infection
Pathogenesis: Septic Arthritis
Outline the Pathogenesis for Septic Arthritis
Synovial membrane is highly vascularized
Therefore, bacteria can easily enter the synovial joint via the blood stream
There will be inflammatory reaction with Seropurulent exudate and and increase in synovial fluid
Therefore, as pus appears in the joint, the articular cartilage is eroded and destroyed.
Partly by the bacterial enzyme and partly by the enzyme released from Synovium, Inflammatory cell and Pus
Describe the effects of Septic Arthritis on Infants, Children and Adults
Infants
Septic arthritis destroys the epiphysis, which is still largely cartilaginous
Children
Septic arthritis causes vascular occlusion which leads to necrosis of epiphyseal bone
Adult
Effect is confined on articular cartilage.
Extensive erosion can occur due synovial proliferation and in growth
Aetiology: Causes of Septic Arthritis
List the causes of Septic Arthritis in Neonates and Infants, Children younger than 5, Healthy kids older than 5, IVDU, Sexually active Individuals and Others
Neonates and Infants
Staphylococcus aureus
Candida species
Children younger than 5
Staphylococcus aureus
Streptococcus pyogenes
Healthy kids older than 5
Staphylococcus aureus
Streptococcus pyogenes
IV Drug Users
GNB
Staphylococcus aureus
**Can be either of these organisms
Sexually Active Individuals
Neisseria gonorrhoeae
Other
Mycobacterium
Fungi
**Usually has a slow onset and TB has predilection for spine
Prosthetic Joint Infections
Define Prosthetic Joints
Prosthetic Joints are made of metals or plastic, most commonly polyethylene inlay between metal shell and metal head
Bone cement also known as PMMA is commonly employed at the metal-bone surface
Material used are those that do NOT cause inflammation in the absence of an infection such as:
Screws
Plates
Wires and pin
Intramedullary rods and nails
Spinal Fixation devices
External Fixation devices
Prosthetic Joint Infection
Prosthetic joint infection is an infection that involved the joint prosthesis and adjacent tissue
Classification of Prosthetic Joint Infections
Classify Prosthetic Joint Infection
Prosthetic Joint infections are classified as either: Early, Delayed or Late
Early Prosthetic Joint infections
Infection occurs within 3 months after implantation
Commonly Staphylococcus aureus
Results in Fever, Joint Pain, Swelling, Wound discharge
Delayed Prosthetic Joint infections
Infections occurs with in 3 to 24 months after implantation
Commonly coagulase-negative staphylococci
Results Joint Pain, maybe Fever, and Intermittent discharge
Late Prosthetic Joint infections
Infections occurs later than 24 months after implantation
Hematogenous
Acute, onset symptoms in previously well function joint
NOTE: Management of Prosthetic Joint infections depends on the classification of the PJI as this allows you to administer the appropriate antibiotic
Clinical Presentation of Prosthetic Joint infections
Describe the clinical presentation of Acute and Chronic Prosthetic Joint infections
Acute Prosthetic Joint infections
In Acute Prosthetic Joint infections:
Local signs and symptoms such as:
Severe pain
Swelling
Erythema
Warmth at infected joint
Fever are common
Chronic Prosthetic Joint infections
Pain
Loosening of Prosthesis at bone-cement interface
Sinus tract formation with discharge
Microbial Aetiology: Causes of Prosthetic Joint infections
NB!! Most common are Coagulase-negative Staphylococci
Staphylococci capitis
Staphylococcus aureus
Viridans group streptococci
Beta Haemolytic Streptococci
Streptococcus pyogenes
Gram negative bacilli
Anaerobes
Pathogenesis of Prosthetic Joint infections
Describe the Pathogenesis of Prosthetic Joint infections
The pathogenesis of implant-associated infection involves the interaction between the Host, the Implant and the Microorganism
The minimal infection doses decreases in the presence of a foreign body
The source of majority of infections is:
Intraoperative contamination from air-borne pathogens in the operating room,
Microorganisms from the skin of the patient or the operating room staff
However, infection can spread to that prosthetic implant from a Contiguous Focus of overlying or adjacent skin and soft tissue
or by hematogenous route from a number of anatomic sites such as Oropharynx, GI tract and GU tract
The incidence of Prosthetic Joint infections is highest during the 1st six months after implantation and then declines afterwards
Once bacteria attach to surface of the prothesis, a complex biofilm that surrounds the bacteria develops.
Biofilm
Define the term Biofilm
Biofilm is a collection of surface-associated microbial cells that is enclosed in an extracellular polymeric substance matrix
Biofilm protects bacteria during slow growth from antimicrobial treatment, and also evades immune response
Slow growing bacteria are harder to kill with antibiotics
Laboratory Diagnosis
Outline the General Laboratory Diagnosis
Laboratory Analysis
Leukocyte Count (WBC)
Elevated in 1/3 of acute osteomyelitis
Erythrocyte Sedimentation Rate (ESR)
Elevated in BOTH acute and chronic osteomyelitis
C-Reactive Proteins
Most sensitive test and is elevated in 97% of cases
Microbiology
Gram Stain, Acid-fast stain from MTB
Cell count: Synovial fluid with elevated neutrophils in septic arthritis
Or inoculation of fluid in blood culture bottle for greater yield
Blood cultures are negative but may be used to guide therapy in hematogenous osteomyelitis
Sinus Tract Cultures: not reliable for guiding antibiotic therapy
Cultures of bone, fluid, pus or tissue: is a GOLD STANDARD for guiding antibiotic therapy
PCR or Squencing
**NOTE: It is better to send culture to the lab before starting antibiotics if possible
Management (General)
Outline the Management of General Infection
Immediate antibiotics are not necessary unless septic patient
Important to make diagnosis first
Treatment duration is prolonged
Surgical management involves the removal of necrotic bone, removal of hardware or prosthetic joint
Medical management includes antibiotic treatment which can be either
Empiric, these types of antibiotic are use when the organism of cause is unknown
Directed: Antibiotics are used when organism and susceptibilities are known
Duration of antibiotics
Outline the duration for Antibiotics used in Osteomyelitis, Septic Arthritis and Prosthetic Joint infections
Osteomyelitis
Antibiotics are used for 4 to 6 weeks
Septic arthritis
Treatment duration is about 4 weeks
Prosthetic/ Hardware related infections
Treatment duration is 6 weeks usually Intravenous Vein is used, because oral does NOT achieve adequate levels
may need longer suppressive therapy if Prosthetic Device is retained
Rifampicin may be used in combination for Biofilms
Label the following
Chronic post-operative chronic osteomyelitis
