<s>[INST] context: Coagulase negative staphylococci fRef. Harrison 17th /e p 839 & 16th/e. p 777. 778] Intravascular catheter related infections Indwelling vascular catheters are a leading source of bloodstream infections. Amongst indwelling vascular catheters, central venous catheters are the most common culprits. Pathogenesis There are four potential sources for catheter related infections ? 1) The skin inseion site 2) The catheter hub 3) Hematogenous seeding from a distant infection 4) Contaminated infilsate The skin inseion site and the catheter hub are by for the two most impoant sources. Approximately 65% of catheter related infections originate from the skin flora, 30% from the contaminated hub and 5% from other pathways. For sho term catheters, skin contamination is the most likely mechani.sm of pathogenesis. On the other hand, for long term catheters, hub contamination is more frequent because such catheters often have to be intercepted and manipulated. Skin organisms migrate from the skin inseion site along the external surface of catheter, colonizing the distal intravascular tip of the catheter, and ultimately causing blood-stream infection. On the other hand, in hub related infections, organisms are usually introduced into the hub from the hands of medical personnel and the organisms migrate along the internal surface of the catheter, where they can cause a bloodstream infection. Microbiology Most of the micro-organisms implicated in CRIs arise from the skin flora. Staphylococci are the most frequently isolated pathogens, paricularly coagulase-negative staphylococci. Etiology of catheter related infection Microorganism Percentage * Coagulase negative staphylococci 30 - 40 * Staph aureus 5-10 * Enterococci 4 - 6 * Candida spp. 3 - 6 * Pseudonzonas aeruginosa 2 - 5 * Enterobacter spp 1 - 4 * Acinetobacter spp. 1 - 2 * Serratia spp. <1 * Others < 1 - 5 [/INST] question: Most common catheter induced blood infection is due to | options: A: >Staphylococcus aureus B: >Coagulase negative staphylococci C: >Gram negative bacilli D: >Candida | answer: B </s>