First tweetorial of the new academic year. Coagulase negative Staphylococci (CoNS) bacteremia is a frequent ID consult. So how do the pros handle the CoNS? Here is a quick generalized approach I use by creating a mnemonic out of CoNS. 1/10
First, remember that coagulase is a test which is used to differentiate coagulase negative Staphylococci from S. aureus, which is coagulase positive and always a pathogen. Image from microbiologyinfo.com. 2/10 
CoNS are a common blood culture contaminant. Studies have estimated that CoNS make up 70-80% of all blood culture contaminants. Amongst CoNS bacteremia, felt to be a contaminant anywhere from 60-80% of the time (Clin Microbiol Rev. 2006 Oct; 19(4): 788–802.) 3/10
The real question for the ID consultant is often, is this bacteremia real? Stated simply, how do we identify those 20-40% of true bacteremias? Enter the CONS mnemonic! Clinical Picture, Ortho/Other, Number of cultures, Species identified. 4/10
Clinical Picture. Why were blood cultures obtained? Did the patient have signs/symptoms of infection? Is it the type of infection where a CoNS would make sense as pathogen (i.e. unusual for pneumonia)? Is the patient on therapy? 5/10
Ortho/Other. Does the patient have ANY implant? CoNS like to make biofilm. For common implants, CoNS cause anywhere from 20-45% of infections! 20% in central lines and orthopedic implants, 33% of VP shunts, 45% of cardiac devices. Don’t forget prosthetic valves either. 6/10
Number of cultures. The number of cultures that are positive, both within a set and in total, can help predict true bacteremia. In this same paper, having 3 or more positive cultures was always associated with true disease. 7/10
Species identified. There are 2 important points here. The first is a coagulase negative staph which always is a pathogen. It can give you a false + slide coagulase test and be mistaken for S. aureus, but a tube coagulase will be negative. This is Staphylococcus lugdunensis 8/10
Second, Staphylococcus epidermidis is the most common CoNS isolated from device infections. 9/10
So remember these 4 steps to tackle CoNS bacteremia. Clinical picture, Ortho/Other implants, Number of positive cultures, Species identified (CONS). Here is a nerdy poem to summarize. 10/10
