Head lice infestation is diagnosed by finding at least one live louse on visual inspection. Visualization can be improved by using a bright light and magnifying lens, and by combing the hair with a lice comb (fine-toothed comb available at most drug stores that is also known as a nit comb) and examining the comb teeth. Lice are commonly found behind the ears and on the back of the neck. When lice are found in one family member, the entire family should be examined.
Physicians should not initiate therapy unless live lice are observed. Finding only nits (lice eggs) on examination does not indicate current infestation. One prospective study found that of 91 school-aged children with live lice and/or nits, only 18% of those with nits alone and no live lice developed an active lice infestation during 14 days of observation. Nits may remain on the hair for months after successful treatment and can be confused with dandruff, hair spray debris, or dirt particles. The American Academy of Pediatrics does not recommend "no-nit" policies at schools and day cares because nits alone do not indicate an active infestation. Children should not be kept out of school during treatment, even with active infestation, because the likelihood of transmission is low, and this can result in significant absences.[1,8]
Body lice should be suspected in patients with pruritus who live in crowded conditions or have poor hygiene. Because body lice lay their eggs in cloth fibers, diagnosis is confirmed with identification of body lice or nits in the seams of clothing. If pubic lice or nits are identified, the patient should be evaluated for sexually transmitted infections.[9,10]
Am Fam Physician. 2019;99(10):635-642. © 2019 American Academy of Family Physicians