How common is sepsis with ecthyma gangrenosum?

Very rare: I have never taken care of a patient with this despite working in an ICU for 7 years at a major referral center. There not even any case series published - just case reports, indicating that no one has been able to even accumulate enough cases at one institution to document more than a few.

About 100%: Ecthyma gangrenosum is a skin lesion which occurs during sepsis with gram-negative bacilli, most often pseudomonas aeruginosa, but has been documented with several other pathogens. Sepsis is the cause, the skin lesion is the result.

Not very: Ecthyma gangrenosum is characteristic of pseudomonas aeruginosa sepsis but can be caused by a variety of other bacteria. It is reported to occur in 1.3%-2.8% of septic patients. I have seen it usually in immune suppressed, agranulocytic cancer patients.