Cortisone reduces your immune response, that's how it reduces swelling etc... So actually this kind of secondary infection is expected.
Actually the hand surgeon @ the VA told me it was a steroid combined with a numbing agent.
I never actually saw the name of what they used but it felt immensely better within a day or two and lasted for months with no ill effects I can discern.
I guess it's likely it might have been cortisone - I'll investigate further.