Chapter 13: Fungal, Viral & Bacterial Skin Infections

Bacterial dermatologic issues range from superficial contagions like impetigo (often caused by S. aureus or Group A Streptococcus [GAS]), to severe conditions requiring prompt intervention, such as cellulitis, diabetic foot infection (DFI), and life-threatening necrotizing fasciitis. Management of bacterial infections necessitates meticulous wound care, hygiene, and the empirical use of broad-spectrum antibiotics (like penicillinase-resistant penicillins or cephalosporins), often requiring coverage for drug-resistant organisms like MRSA using agents such as vancomycin or SMX–TMP. Fungal infections, categorized as tinea (affecting specific body sites like the scalp, feet, or nails) or candidiasis, are typically treated topically with azoles or allylamines, but infections involving the hair (tinea capitis) or nails (tinea unguium/onychomycosis) demand systemic antifungals, including griseofulvin or terbinafine. Caution is advised regarding the hepatotoxicity and drug interaction profile of oral antifungals. The chapter also explores viral infections, including Herpes Simplex Virus Type 1 (HSV-1) and Varicella-Zoster Virus (VZV), which causes chickenpox and shingles (herpes zoster). Since herpes viruses reside latently in ganglia, treatment with systemic antivirals like acyclovir, famciclovir, or valacyclovir aims to shorten symptom duration, suppress outbreaks, and mitigate complications like postherpetic neuralgia. Finally, warts (verrucae), caused by Human Papillomavirus (HPV), are primarily treated with keratolytic agents such as topical salicylic acid. Throughout, clinical decision-making emphasizes selecting the appropriate agent based on the infection type, patient risk factors (e.g., diabetes, immune status), local resistance patterns, and minimizing potential adverse effects.