Accurate diagnosis of an active head louse infection is fundamental to deciding whether treatment is needed. In the past, the presence of apparently viable louse eggs close to the scalp was considered sufficient evidence of an active infection. Now only the presence of mobile stages is considered adequate evidence.2 A recent cohort study (50 people) confirmed that the presence of eggs close to the scalp is a limited risk factor. Children screened by direct observation of the scalp, and found only to have louse eggs, were evaluated again 14 days later. Those with five eggs or more within 6 mm of the scalp were more likely to develop an active infection than those with fewer than five eggs (7/22 versus 2/28; RR 4-5, CI 1-0-19-4). It was concluded that many children are excluded from school or treated unnecessarily and that repeated examinations to determine whether an infection develops would be more beneficial.35
Unnecessary treatments and school exclusions also arise because caregivers and health professionals misdiagnose items found in the hair. An observational study evaluating 614 samples of presumed head lice found that only 364 (59%) were louse related, showing that better diagnostic tools are required.36
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