Nosocomial Infections and Staphylococcus aureus

Nosocomial Infections (HAIs)

• Nosocomial infections, also known as Hospital Acquired Infections (HAIs) or Healthcare Associated Infections (HCAIs), are infections that develop during a hospital stay but were not present at admission.
• Approximately 300,000 patients in England acquire infections after care within the NHS annually, costing roughly £1 billion.
• In developing countries, 1 in 10 hospitalized patients acquire at least one HAI.
• HAIs are often associated with medical devices or surgical wounds, ranging from infections associated with catheters to serious blood infections associated with ventilators or surgical site infections.
• These infections are caused by various bacterial, viral, and bacterial pathogens, including antibiotic-resistant bacteria like Acinetobacter baumannii, ESBL-producing Enterobacteriaceae, Staphylococcus aureus, and Clostridium difficile.

Staphylococcus aureus (S. aureus)

• S. aureus is a Gram-positive coccus appearing in grape-like clusters. It produces a golden pigment.
• S. aureus produces coagulase, an enzyme causing blood clotting, distinguishing it from other coagulase-negative staphylococci.
• It's a facultative anaerobe, surviving with or without oxygen.
• S. aureus is found in the nostrils and skin of approximately 30% of the population, acting as carriers without causing infection.

S. aureus Infections

• S. aureus can cause various infections, including skin and soft tissue infections (SSTIs), bone and joint infections, heart valve infections, pneumonia, and infections related to medical devices or implanted materials.
• S. aureus has developed resistance to various antibiotics.
• Historically, beta-lactamases inactivated penicillin but methicillin-resistant strains (MRSA) and other resistant strains have risen.
• MRSA is a significant cause of bacteremia, with approximately 12,878 cases in the UK between 2018-2019. Mortality rates for these cases, were ~26%.
• Vancomycin-intermediate resistant S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA) strains exhibiting resistance to vancomycin are also on the rise. This complicates treatment.
• Treating S. aureus infections has become significantly more complicated and challenging due to increasing resistance.

Hospital Transmission

• S. aureus transmission in hospitals can occur endogenously (from existing colonization within the body) or exogenously (through person-to-person contact with skin, equipment, or airborne particles).
• Hospitals implement measures to prevent and control MRSA spread including hand hygiene, general cleanliness, covering wounds, and using appropriate protective equipment.

Treatment and Recurrence

• Treatment drug choices for S. aureus infections vary based on the type of infection, e.g. Daptomycin for MSSA/MRSA and Linezolid for MRSA infections.
• Recurrence (relapse) of S. aureus infections, particularly in prosthetic joint infections and SSTIs, is common, often due to lingering bacteria in biofilm or cells.
• Recurrence rates can range between 10-50% for S aureus infections.