Could be Fungal infection
Hi. Thanks for posting at HealthcareMagic.
Groin folds are a common site of fungal infection. Its because of the fact that sweat gets trapped in between groin folds and gives rise to an environment conducive for fungal growth. Hot, humid weather predisposes it even more.
If i were the treating dermatologist
i would have asked to apply a topical steroid+antifungal cream twice daily for 2 - 4 weeks.
Use of an antifungal dusting powder like Clotrimazole
dusting powder would prevent it from recurring.