• Common infestation, particularly in children; endemic worldwide
• Parasite is a blood-sucking insect 2-3 mm long with powerful claws found exclusively in humans (no animal host).
• Infestation involves hair shafts and scalp.
• Not a serious health hazard but associated with time lost from school and work
• 132.0 pediculus capitis (head louse)
• 132.3 mixed pediculosis infestation
• 132.9 pediculosis, unspecified
Who is most affected
• Healthy children, especially girls
• Adults with poor hygiene
• Less common in African Americans (possibly due to differences in hair texture)
• Estimated 6-12 million U.S. cases per year
• Head-to-head (i.e., shared combs) especially in schools, child-care centers, or “sleepover” camps
• Infected household members and overcrowded living conditions
• Poor hygiene (in adults)
• Factors not associated with increased risk
— Hygiene (in children)
— Length of hair
— Socioeconomic class (all affected)
Complications and associated conditions
• Secondary bacterial skin infection (e.g., impetigo) is rare.
• Other louse infestation or scabies (especially in indigent, homeless, or refugee populations)
Symptoms and diagnosis
• Pruritus/sensation of “something crawling on head”
• Occasionally fever, lymphadenopathy, headache, rash, malaise, or irritability
• Often asymptomatic
• Procedure for scalp inspection
— Wet and comb hair.
— Search with strong light (Wood’s lamp may facilitate detection) and magnifying glass using fine-toothed comb (teeth 0.2-0.3 mm apart) to trap lice.
— Insert comb near crown at scalp; comb entire head systematically at least twice, examining comb after each stroke.
— Nits visible at proximal ends of hair shafts (may require magnifying lens)
— Most easily seen at nape of neck or behind ears at hairline
— Height of nits above scalp indicates duration of infestation (1 cm = one month).
• Rule out
— Other causes of scalp pruritus (hairstyling products, contact or seborrheic dermatitis, etc.)
— “Pseudonits” such as dandruff, dried hairspray, dirt, Trichosporon beigelii fungi (“white piedra”), or “hair casts” (desquamated epithelial hair plug)
Topical pediculicides (FDA approved)
• Resistance to common pediculicides reported to be emerging in United States
— Approved for adults and children >2 months old
— American Academy of Pediatrics (AAP) recommends as treatment of choice.
— Reported adverse effects include asthma exacerbation, contact dermatitis, mild/transient burning, and pruritus.
— Approved for adults and children >6 years old
— Recommended when permethrin resistance suspected
— Flammable (do not use near hair dryer, cigarettes, etc.)
— May cause irritation of skin and scalp
— Second-line therapy for patients who cannot tolerate or have failed first-line treatment with safer medications (avoid in infants, children, and elderly)
— Associated with persistent pruritus after treatment (not an indication for re-treatment)
— Pharmaceutical use banned in California since 2002