Hi, I had gone through your query and understand your concerns. it is quite unlucky to have discharge from a sternal wound after going through bypass surgery. i think culture from the discharge has already been done and as you said there is no infection. however, atypical microorganisms like Mycobacteria, Actinomycetes INFECTION MAY ALSO BE A POSSIBILITY . chronic ostemylitis with discharging sinus that discharges on and off is another probability.i think this should be looked into and you should consult a infectious disease specialist as well as an orthopedist and cardio-thoracic surgeon to seek their combined opinion. with proper diagnosis and corrective measures, i think your problem will be solved but it will need prolonged treatment with proper antibiotics and surgical debridement if necessary in speficic cases.