10.2 Infectious Dermatoses, Infestations & Warts

Infectious dermatoses, infestations, and warts are high-volume primary-care skin visits. Domain II is the morphology: honey crust, annular scale, satellite pustules, umbilicated papules, burrows, nits. Domain III is the drug and the procedure. The 2023 CPNP-PC outline names incision and drainage and wart removal among office procedures. You should be able to choose mupirocin versus an oral anti-staphylococcal agent, know that tinea capitis is an oral disease, treat the household for scabies, destroy a wart with a method you can name, and not send HSV-on-eczema home as worse atopic dermatitis.

Clinic opening. A school nurse sends a 6-year-old for ringworm of the scalp. A cream has been on the hair for three weeks. There are black-dot patches, scale, and posterior cervical nodes. If you refill clotrimazole and skip oral griseofulvin or terbinafine, you failed the highest-yield trap in this section.

Impetigo

Nonbullous impetigo is honey-colored crust on an erythematous base, usually perinasal or on extremities, from Staphylococcus aureus or Streptococcus pyogenes. Bullous impetigo is toxin-mediated S. aureus with flaccid bullae. Limited, localized nonbullous disease: topical mupirocin (typically three times daily for about 5 days) is first-line. Oral therapy (cephalexin when MSSA/strep is likely; a MRSA-active agent when local epidemiology, an associated abscess, or failure points that way) is for widespread lesions, bullous disease, systemic signs, outbreaks that cannot be contained, or involvement topical therapy cannot cover. Return-to-school is usually after 24 hours of effective therapy when lesions can be covered — confirm local public-health policy rather than inventing a day count.

Do not incision-and-drain flat impetigo crusts. Do not treat a single honey crust with a 10-day fluoroquinolone just in case.

Cellulitis versus erysipelas versus abscess

I&D is a named CPNP-PC procedure: sterile field, adequate anesthesia, incision, drainage, breakup of loculations, packing when indicated, and wound-care teaching. Antibiotics are adjunctive for surrounding cellulitis, systemic signs, immunocompromise, facial/hand/genital high-risk sites, or incomplete drainage. They are not a substitute for draining a mature abscess. Home needle pokes are not a plan. Rapidly spreading, orbital, or toxic presentations leave the office for emergency care.

Clinic vignette. A 9-year-old soccer player has a 2-cm, fluctuant thigh nodule after a turf abrasion. Afebrile, about 1 cm of surrounding erythema. Plan: office I&D (or same-day procedure clinic), wound care, culture when you drain if MRSA is a concern, and antibiotics if the cellulitic rim is significant — not 10 days of cephalexin and hope it opens.

Tinea corporis and tinea capitis

Tinea corporis is an annular, scaly plaque with central clearing and an active edge. Confirm with KOH when the diagnosis is uncertain. Treatment: a topical allylamine (terbinafine) or an azole for 2–4 weeks, continuing about 1 week after visual clearance. Do not use combination steroid-antifungal creams as the default — they mask and can worsen tinea (tinea incognito).

Tinea capitis is a scalp dermatophyte infection (often Trichophyton tonsurans in the United States): patchy alopecia, black dots, scale, kerion (a boggy inflammatory mass), and cervical lymphadenopathy. Topical cream alone fails because the follicle is deep. Treat with oral griseofulvin or oral terbinafine (choice and duration depend on organism and age; terbinafine is often preferred for Trichophyton; griseofulvin remains widely used, especially when Microsporum is suspected). Adjunctive antifungal shampoo (selenium sulfide or ketoconazole) reduces surface spores and household spread; it is not monotherapy. Culture or KOH before or at start when feasible. A kerion still needs the oral antifungal; steroids are a specialist adjunct, not a reason to skip the oral agent. Many districts allow return to school once oral therapy has started; follow local rules.

Trap: treating tinea capitis with cream only.

Candida diaper versus irritant

Irritant diaper dermatitis is erythema on convex surfaces that spares folds, from wetness and friction. Treat with frequent changes, super-absorbent diapers, and a thick barrier (zinc oxide, petrolatum). Candidal diaper dermatitis is beefy red, involves folds, and shows satellite papules or pustules. Treat with topical nystatin or an imidazole plus barrier care. Do not use a combination high-potency steroid-antifungal on infant skin as a convenience cream.

HSV, varicella, and zoster

HSV (usually HSV-1) is clustered vesicles on an erythematous base: gingivostomatitis, herpes labialis, herpetic whitlow, or eczema herpeticum. Primary gingivostomatitis is painful; hydration is the safety check. Oral acyclovir or valacyclovir can be used when started early in selected cases. Eczema herpeticum and neonatal HSV are emergencies. Missing HSV on eczematous skin is the paired trap with cream-only tinea capitis.

Varicella is crops of papules, vesicles, and crusts in different stages, pruritic and centripetal. Vaccinated children may have milder breakthrough disease. Supportive care in healthy children; antivirals for high-risk hosts; isolation counseling per public health. Zoster is dermatomal painful vesicles in a child who had varicella or vaccine. Healthy children often need supportive care; involvement of the eye (Hutchinson sign, V1) is same-day ophthalmology. Do not call dermatomal zoster impetigo in a line.

Molluscum and warts (destruction is on the blueprint)

Molluscum contagiosum (poxvirus) is pearly, umbilicated papules. Watchful waiting is acceptable in mild disease (months to a few years). Treat for bother, secondary infection, numerous genital lesions with autoinoculation counseling, or immunodeficiency. Options: cantharidin in-office, cryotherapy, curettage — shared decision, not mandatory freezing of every bump. Molluscum in the diaper of a toddler is usually autoinoculation, not a default sexual-abuse diagnosis.

Warts are HPV. Common, plantar, and flat warts fill after-school clinic slots. Wart removal is a named office procedure. Destruction methods the CPNP-PC should be able to discuss:

• Salicylic acid with occlusion (home, first-line for many common warts)
• Cryotherapy with liquid nitrogen (office)
• Cantharidin (office, blistering)
• Curettage or excision / snip of filiform warts when indicated

Counsel that recurrence is common because HPV lives in surrounding skin. Do not promise a one-freeze cure. Anogenital warts in a young child require a thoughtful sexual-abuse assessment. Not every case is abuse — vertical transmission and innocent autoinoculation occur — but you do not skip the history.

Scabies and lice

Scabies (Sarcoptes scabiei) is intense itch, worse at night; burrows on wrists, finger webs, and the belt line; in infants, palms, soles, axillae, and often the scalp and face. Treat with permethrin 5% cream: neck down in older children, include head and neck in infants, leave on 8–14 hours, rinse, and commonly repeat in 1 week. Treat household contacts at the same time even if they look asymptomatic. Wash linens and clothes in hot cycles or bag them for several days. Itch can persist 2–4 weeks after a successful kill (dead-mite hypersensitivity) — that is not automatic treatment failure. Do not use lindane as first-line in children.

Head lice: a live louse or viable nits near the scalp. Permethrin 1% or pyrethrin with piperonyl butoxide are common first-line OTC options, plus wet combing, with retreatment per the product. Treat infested household members. Hats and linens: wash/dry hot or bag. Classroom-wide spraying is not the plan. No-nit policies are generally not required for return once treated.

When to refer

Refer or escalate the same day for eczema herpeticum, orbital or facial cellulitis with toxicity, necrotizing or rapidly spreading infection, suspected neonatal HSV, a kerion that is failing or very inflammatory, extensive tinea in an immunocompromised child, anogenital warts with abuse concern, crusted (Norwegian) scabies, and any progressive lesion you cannot diagnose.

Exam traps. Tinea capitis plus cream only. HSV punched-out vesicles labeled as impetigo or flare. Abscess treated with antibiotics and no drainage. Scabies cream on the index child but not the household. Warts: knowing that destruction methods and wart removal are in your procedure set, not only duct-tape folklore.

Clinic close. Honey crust, few lesions, well child: mupirocin. Honey crust everywhere or bullous or febrile: oral therapy. Fluctuant pocket: I&D. Annular body plaque: topical antifungal. Scalp black dots and nodes: oral griseofulvin or terbinafine. Beefy diaper with satellites: candida, not irritant. Umbilicated pearls: molluscum, often watch. Verrucous papule: name a destruction method. Night itch and burrows: permethrin 5% and the whole house. Punched-out pits on eczema: HSV, not a steroid bump.