Internal rot normally starts when fungi infect the flowers or young fruit. These latent infections lie dormant as the fruit develops. Once the fruit starts to ripen, the disease develops rapidly, leaving no sign of the disease on the outside of the fruit.
The disease does not move from fruit to fruit but disease can be transmitted by seed. Hot water treatments are effective at controlling all the organisms known to cause this disease.
I hope this helps.
you can use a foliar with a 0.05% v/v plant safe surfactant and a compost tea during flowering to help prevent this. I've had good success with a product called inocucor, it also seems to help with pod setting during less than ideal conditions.