Bacterial Hemorrhagic Septicemia is not contagious, it's a bacterial infection that has entered the bloodstream causing poisoning, it is fatal when untreated. Conversely, Viral Hemorrhagic Septicemia is VERY contagious and fatal - it comes with other visible symptoms like pop-eye & ulcers. BHS is a symptom, has an underlying cause whether it be water quality (ammonia), ectoparasites, injury (tankmates/rocks/small tanks) etc.
The reason my treatment choice is erythromycin: it is commonly found in fish stores, even Petco, whereas kanamycin is most likely an online order. I don't doubt the effectiveness of kanamycin + nitrofurazone combo, but nitrofurazone has a low potency relative to other antibiotics, thus the need for a higher dose. I understand the combo can be synergistic, but not necessary in this situation.
Antibiotics are best administered when fed, keeping the fish in the tank and feeding erythromycin will eliminate additional stress on the immune system (brought on by QT) and you would likely have 2 days of treatment underway while you may still be trying to trap your fish for quarantine with the other.
I have seen improvement with emycin in 2-3 days and if I ran into a case where it didn't work (bacteria was resistant) I would then put the fish into QT and treat with Doxycycline, powerful stuff.