Why are clostridium difficile infections hard to treat?

It produces spores: Partly it is the persons immune system and general health that makes it recur more often. The main problem is it comes back after treatment. Clostridium produces endospores. Endospore is is a tough structure in which the bacteria is dormant and not reproducing. Antibiotics don't affect the spores so after the symptoms are gone, the spores activate and then cause reinfection.

Relapses: C. Difficile infections are not generally hard to treat and more than 90% initially respond well to vancomycin or Metronidazole treatment. The problem is the high rate of relapse after treatment of 20-30%. The risk of future relapses increases after each relapse.