Device Related Infections

Infections associated with implanted or indwelling medical devices. These include:

• intravascular catheters (both peripheral and central)
• prosthetic joints
• cardiac implantable electronic devices
• prosthetic heart valves
• other implanted hardware

They are characterised by the formation of a bacterial biofilm on the device surface. This fundamentally alters both the microbiology and the management approach compared with infection in native, device free tissue.

Device removal is frequently an essential component of successful treatment given the limited ability of antibiotic therapy alone to eradicate biofilm associated infection.

Pathophysiology

• Bacteria adherent to a foreign device surface form a biofilm: an organised structure embedded within a self produced extracellular polymeric matrix.
• The matrix provides substantial protection from both host immune defences and antibiotic penetration.
• Organisms within the biofilm frequently exist in a metabolically dormant, slow growing state, which further reduces susceptibility to antibiotics that typically target actively dividing bacteria.
• This explains why device associated infection is characteristically far more difficult to eradicate with antibiotics alone than equivalent infection in native tissue.
• Coagulase negative staphylococci (particularly Staphylococcus epidermidis) are a leading cause of device associated infection, given their particular propensity for biofilm formation. They are generally regarded as low virulence organisms in other contexts.
• Staphylococcus aureus is less specifically adapted to biofilm formation but remains a major and often more acutely aggressive cause of device related infection across all device types.

• Intravascular catheter related infection presents with local signs at the insertion site (erythema, tenderness, purulent discharge) in a proportion of cases.
• Bacteraemia without prominent local signs is common, particularly with central venous catheters.
• Fever or clinical sepsis in a patient with an indwelling line should therefore always prompt consideration of catheter related bloodstream infection, even in the absence of obvious local findings.
• Prosthetic joint infection presents either acutely or with a more indolent, chronic course.
• Acute presentation is typically within weeks of implantation, with fever, pain, swelling and wound discharge.
• Lower grade, biofilm associated organisms such as coagulase negative staphylococci characteristically cause a chronic presentation months to years after implantation. Features are persistent joint pain, progressive loosening of the prosthesis on imaging and, in some cases, a discharging sinus tract.
• The chronic presentation is often without significant systemic upset or markedly elevated inflammatory markers.
• Cardiac implantable electronic device infection can present as a localised pocket infection at the generator site: erythema, swelling, discharge, sometimes with erosion of the device through the overlying skin.
• More seriously, it can present as lead associated endocarditis, with bacteraemia and, on echocardiography, vegetation formation on the intracardiac portion of the leads.
• Prosthetic valve endocarditis, addressed further under infective endocarditis, presents similarly to native valve disease, though with a particular association with staphylococcal and coagulase negative staphylococcal infection.
• It carries a generally higher associated morbidity and mortality, with a greater likelihood of requiring surgical intervention alongside antibiotic therapy.

• Blood cultures are the essential diagnostic approach for suspected intravascular device infection.
• Draw them both peripherally and, where a suspected infected catheter remains in place, through the catheter itself.
• A catheter sample that turns positive significantly earlier than the peripheral sample (differential time to positivity) supports a catheter related source.
• Catheter tip culture, following removal, using a semiquantitative or quantitative technique, supports diagnosis where blood cultures alone are inconclusive, though should not be the sole basis for diagnosis given the potential for contamination during removal.
• Prosthetic joint infection diagnosis integrates clinical features, inflammatory markers, and synovial fluid analysis (white cell count and differential).
• Joint specific thresholds differ from those used for native joint septic arthritis, given the altered local inflammatory milieu around a prosthesis.
• Most importantly, obtain multiple intraoperative tissue samples for culture at the time of any surgical intervention. Multiple deep tissue samples are more sensitive than synovial fluid aspiration alone, particularly for lower virulence, biofilm associated organisms.
• Sonication of a removed prosthetic device, a specialised technique that dislodges adherent biofilm bacteria into solution for culture, offers improved sensitivity compared with conventional tissue culture alone, particularly valuable for patients who have received prior antibiotic therapy, which can suppress conventional culture yield.
• Echocardiography is indicated for suspected cardiac implantable electronic device or prosthetic valve infection, with a low threshold for transoesophageal imaging given its superior sensitivity, particularly for prosthetic material.
• Nuclear medicine imaging (labelled white cell scan) may have a role in specific diagnostically uncertain scenarios, particularly for prosthetic joint infection, where standard imaging modalities are limited by artefact from the metal implant itself.

• Device removal is frequently an essential component of successful treatment, reflecting the fundamental biofilm related limitation of antibiotic therapy alone.
• The decision on removal, retention, or staged replacement is individualised according to the device type, the chronicity and severity of infection, the causative organism, and the feasibility and risk of removal in the individual patient.
• Intravascular catheter related bloodstream infection generally requires prompt removal of the implicated catheter. This applies particularly to infection caused by Staphylococcus aureus or Candida species, or in the context of complicated infection (persistent bacteraemia, evidence of metastatic seeding, septic thrombophlebitis).
• Antibiotic therapy duration is guided by the specific organism and the presence of any complications.
• Uncomplicated Staphylococcus aureus bacteraemia, with prompt catheter removal and clearance of bacteraemia, typically needs a minimum of two weeks. Duration is extended substantially for complicated infection.
• Prosthetic joint infection management follows a spectrum according to timing and stability.
• Early infection (generally within four weeks of implantation, or acute haematogenous infection of a previously well functioning prosthesis) with a stable, well fixed implant may be managed with debridement, antibiotics and implant retention.
• This is combined with prolonged antibiotic therapy, typically including an extended oral course with an agent possessing good biofilm activity: rifampicin combined with a fluoroquinolone for staphylococcal infection, where susceptibility allows.
• Specific evidence supports rifampicin combination therapy for retained implant infection.
• More established or chronic prosthetic joint infection, or infection with an unstable, loose implant, generally requires implant removal.
• One stage exchange is removal and immediate reimplantation of a new prosthesis. It is more commonly used in specific centres and for certain organism and patient profiles.
• Two stage exchange is more common: removal of the infected implant, placement of an antibiotic impregnated cement spacer, a prolonged course of targeted intravenous antibiotic therapy, and subsequent reimplantation of a new prosthesis once infection is confirmed cleared.
• The specific approach is determined through specialist orthopaedic and infectious disease multidisciplinary discussion.
• Cardiac implantable electronic device infection generally requires complete removal of the entire system (generator and all leads), given the substantial risk of relapse with partial removal or antibiotic therapy alone, particularly with confirmed lead associated endocarditis.
• Prolonged targeted antibiotic therapy accompanies removal.
• Reimplantation of a new device, where an ongoing indication remains, is generally deferred until infection is confirmed cleared, typically after a course of directed antibiotic therapy and negative repeat blood cultures.
• Prosthetic valve endocarditis is managed with prolonged targeted antibiotic therapy as detailed under infective endocarditis.
• Surgical valve replacement is indicated for heart failure from valve dysfunction, uncontrolled infection, significant paravalvular extension or abscess formation, and high embolic risk.
• These follow the same general surgical indication principles as native valve disease, though with a generally lower threshold for surgical intervention, given the typically more aggressive nature and higher complication rate of prosthetic valve infection.
• Specialist infectious disease involvement is strongly recommended for all device related infections given the complexity of antibiotic selection (including consideration of specific biofilm active agents), the frequently prolonged treatment duration required, and the close coordination needed with the relevant surgical specialty regarding device management decisions.