Combing through a child's wet hair seems to be a more accurate way of finding active head lice compared with visual checks, researchers say.

In the March issue of the Journal of the American Medical Association's Archives of Dermatology, doctors in Germany compared the diagnostic accuracy of visual inspection and wet combing for 300 students aged six to 12 at schools with epidemics of head lice in 2007.

Head lice infestation, or Pediculosis capitis, is one of the most common childhood infections, affecting between one and three per cent of six- to 12-year-olds in industrialized countries, the researchers said, citing previous studies.

Head lice may lead to headaches for parents, teachers and health-care providers, but researchers said the diagnostic accuracy of the techniques has never been determined appropriately.

To find out, Dr. Claudia Jahnke of the City Health Department in Braunschweig and her colleagues checked students first by visual inspection, using an applicator stick to part the hair at the temples, behind the ears and on the neck.

A second investigator, who was unaware of the results of the first check, then applied a conditioner to wet the hair and used a fine-toothed comb to look for objects from roots to ends of the hair.

The conditioner was then wiped on white sanitary paper and the investigator looked for any trapped objects with a magnifying glass.

Methods suit different purposes

"Visual inspection underestimated the true prevalence of active infestation by a factor of 3.5," the study's authors wrote.

Wet combing correctly identified active infestations — moving lice  — in 90.5 per cent of the children compared with 28.6 per cent for visual inspections.

But visual inspections were better for finding historic infestations — nits or dead embryos in egg shells — 86.1 per cent compared with 68.4 per cent for wet combing.

Since most children in industrialized countries carry only a few lice, the best detection method would identify a single louse while minimizing the potential to miss someone as negative for lice when the child actually has the potential to spread the parasite, the researchers said.

"In this regard, wet combing is the only useful method if active infestation has to be ruled out."

Visual inspection is a better option for looking for historic cases, since it's fast, requires no other resources besides an applicator stick and is more sensitive for finding eggs or nits, the team concluded.

Pohl-Boskamp & Co. KG of Hohenlockstedt, Germany, a producer of a pediculicide and combs, provided the head lice combs free of charge for the study.