The epidemiology of head lice infestation is poorly understood. Many schools treat all children with nits as though they are contagious. Children with nits but no lice are often removed from school until they are treated and all visible nits are removed.


To investigate the probability that children with nits alone will become infested with lice.


Prospective cohort study.


Two metropolitan Atlanta elementary schools.


A total of 1729 children were screened for head lice. Twenty-eight children (1.6%) had lice, whereas 63 (3.6%) had nits without lice. Fifty of the 63 children (79%) with nits alone completed follow-up.

Outcome Measure.

Conversion (ie, becoming infested with lice) within 14 days after initial screening.


Nine of 50 children (18.0%) followed for nits alone converted. Although children who converted did not have significantly more nits than did nonconverters, having nits near the scalp was a risk factor for conversion. Seven of 22 children (31.8%) with ≥5 nits within one fourth inch of the scalp converted, compared with 2 of 28 children (7.1%) with fewer (relative risk: 4.45; 95% confidence interval: 1.03–19.35). This risk remained statistically significant after separately stratifying for sex, recent treatment, and total number of nits.


Although having ≥5 nits within one fourth inch of the scalp was a risk factor for conversion, most children with nits alone did not become infested. Policies requiring exclusion from school and treatment for all children with nits alone are likely excessive. Instead, these children may benefit from repeated examination to exclude the presence of crawling lice.lice, pediculus, lice infestations, pediatrics, school.

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