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March 19, 2009 -- Combing through a child's wet hair rather than a simpler visual inspection may be the best way to detect an active head lice infestation, according to a new study.
Head lice infestation is one of the most common childhood infections, affecting 1% to 3% of 6- to 12-year olds in industrialized countries. The tiny head louse is a parasite that attaches to the scalp and is spread easily among children in close contact, such as classrooms.
But until now, researchers say the accuracy of the two most common methods used to detect head lice and their eggs or nits, wet combing and visual inspection, has not been put to the test.
The results of the study suggest that the wet-comb method is much more accurate at detecting active head lice infestation in children. But visual inspection remains a useful tool for teachers, parents, and other caregivers to measure epidemics of head lice and determine how many children are affected.
"Usually, diagnosis of head lice infestation is made by the visual inspection of the hair and scalp," write researcher Claudia Jahnke, MD, of the City Health Department of Braunschweig, Germany, and colleagues in the Archives of Dermatology. "The alternative is the use of a detection comb, either directly on dry hair or after the hair has been moistened with conditioner. In both cases the hair is systematically combed from the scalp to the ends."
The advantage of the visual inspection method is that it is easy and fast. The wet-comb method, on the other hand, is more time consuming and requires special equipment and instruction.
In the study, researchers compared the effectiveness of the two head lice detection methods in 300 children attending German schools with head lice epidemics in 2007.
The results of the study show the visual inspection method underestimated the prevalence of active head lice infestation by a factor of 3.5.
Wet combing was much better at detecting active head lice infestations, correctly identifying them in 90.5% of children, compared with a 28.6% accuracy rate for visual inspections.
But visual inspections were better at detecting "historic" head lice infestations -- that is, children who have nits in their hair but no lice.
Researchers say that in industrialized countries, most children only carry a few head lice. Therefore, the optimal detection method should identify those with even a single live louse who have the potential to spread the parasite, which makes wet combing the preferred method to detect active infestations.