Unusual skin infection Unusual nail infection Causative agents include bacteria (Staphylococcus aureus, Streptococcus species) causing paronychia, and fungi (dermatophytes, Candida species) causing onychomycosis. Unusual susceptibility to nail infection Unusual nail apparatus infection Increased susceptibility to infection of the nail apparatus, including the nail plate, nail bed, nail matrix, and proximal nail fold, as manifested by recurrent or severe nail infection, or by nail infection caused by an atypical or opportunistic organism.