A 62-year-old man is brought to the emergency department from a homeless shelter due to alcohol intoxication. The patient has no other symptoms or history of significant medical conditions. Examination of the scalp reveals the findings shown in the exhibit.
Which of the following organisms is most likely responsible for this patient's condition?

Question

A 62-year-old man is brought to the emergency department from a homeless shelter due to alcohol intoxication.  The patient has no other symptoms or history of significant medical conditions.  Examination of the scalp reveals the findings shown in the exhibit. 
Which of the following organisms is most likely responsible for this patient's condition?

Quizplus · Accepted Answer

This patient has numerous nits, which are egg casings of the head louse Pediculus humanus capitis. Pediculosis capitis (ie, head lice infestation) is common in school children and adults who come into close contact with infested individuals (eg, sports teams, homeless shelters). Transmission is usually by direct contact, although transmission by fomites (eg, hats, hairbrushes) can also occur. Head lice require multiple blood meals a day and die within 2 days if separated from a host. They do not carry arthropod-borne infection, but the bite can induce a pruritic allergic reaction. Female lice attach their nits to the hair shaft about 0.5 cm from the skin surface; nits further from the surface often represent old egg casings that have hatched and generally do not require treatment. First-line treatment includes topical pediculicides (eg, permethrin, ivermectin). Manual lice removal via wet combing is an alternate treatment for patients for whom standard pediculicides are not feasible (eg, children age <2 years, resource-poor populations). (Choice A) Cimex lectularius (ie, bedbugs) bites present as pruritic, red papules in clusters. The females lay eggs away from the host and do not produce nits. (Choice B) Colonization with Malassezia yeasts is associated with seborrheic dermatitis. On the scalp, this condition can produce white skin flakes in the hair (ie, dandruff). The flakes are not adherent to the hair shaft and are typically found loosely throughout the hair and on the clothing. (Choice D) Pthirus pubis (ie, crab louse, pubic louse) is usually transmitted by sexual contact. The louse is adapted for attaching to thick hair shafts, and the nits are usually found on pubic and other thick hair (eg, eyelashes); however, scalp hair is not typically affected. (Choice E) Sarcoptes scabiei causes scabies, which presents with pruritic papules and burrows on the interdigital and flexural skin of the extremities. The female mite lays eggs in burrows and does not form nits. (Choice F) Trichophyton tonsurans is a dermatophyte that causes tinea capitis, which presents as a scaly, erythematous patch of hair loss. There are often small, black dots that represent broken hair shafts. Educational objective: Pediculus humanus capitis (ie, head lice) infestation is common in school children and adults who come into close contact with infested individuals. Transmission is usually by direct contact. The eggs (nits) are attached to the hair shaft and can be identified on inspection. First-line treatment includes topical pediculicides (eg, permethrin, ivermectin).

A 62-Year-Old Man Is Brought to the Emergency Department from a Homeless