March 16 (HealthDay News) -- Wet-combing a child's hair is better than a visual inspection for detecting active head lice infestation, according to German researchers.

They compared the two methods in 304 students, ages 6 to 12. Each child first underwent a visual inspection, in which an applicator stick was used to part the hair at the temples, behind the ears and on the neck.

A second researcher, who didn't know the results of the visual inspection, then applied a conditioner to wet the hair and combed from hair roots to ends with a fine-toothed comb. The conditioner collected by the comb was wiped on white sanitary paper and any objects collected by the conditioner were examined with a magnifying glass.

Overall, eggs or larvae, called nits, were detected in about 26 percent of the children, and adult or nymph lice were detected in 7 percent.

"Visual inspection underestimated the true prevalence of active infestation by a factor of 3.5," the study authors wrote. Wet-combing accurately identified active infestations in 90 percent of the cases, compared with about 29 percent for visual inspections. But visual inspection was more accurate in identifying previous infestations -- 86 percent vs. 68 percent.

"In contrast to settings in the developing world in which a high intensity of infestation is the rule, in industrialized countries, most children carry only a few lice," the researchers wrote. "In consequence, the optimal detection method should identify even a single louse and should have a high negative predictive value to exclude the possibility that individuals classified as negative for lice are actually false negative with the potential to spread the parasite."

The researchers concluded that "wet-combing is the only useful method if active infestation has to be ruled out."

But, if school or medical officials want to determine the frequency of infestations, visual inspection can be "rapidly performed, requires no additional resources other than a reusable applicator stick and is more sensitive."

The study was published in the March issue of the journal Archives of Dermatology.

SOURCE: JAMA/Archives journals, news release, March 16, 2009