To the Editor: Pediculosis capitis has been well-known since antiquity (
1
). Human infestation can result in psychological frustration for parents and children
(
2
); furthermore, preventive and therapeutic practices, such as head shaving and the
“no-nit” policy of excluding infected children from school, can also induce social
stress.
We sought to synthesize the available evidence regarding the worldwide prevalence
of lice infestation in the 21st century by conducting a literature search of PubMed
and Scopus databases in which we searched for the term pediculosis. We also searched
Google for the terms head lice/pediculosis capitis and individual country names and
evaluated references of the articles and reports retrieved through this search. Eligible
studies were archived from January 1, 2000, to January 18, 2008.
We retrieved 55 studies (Technical Appendix). Most studies referred to schoolchildren,
but some involved refugees, urban slums, child labor, jails, orphanages, and fishing
communities.
Most studies had been conducted in Asia; Turkey was overrepresented. Prevalence varied
from 0.7% to 59% and was higher in girls and women. Of the 29 studies, 24 involved
schoolchildren; the other studies involved refugee children, child laborers, the general
population, street children, jail inmates, and children accompanying their mothers
in prison.
In Europe, prevalence varied from 0.48% to 22.4%. However, 1 study reported a much
higher annual incidence (37.4%) in England (
3
). A study in the Ukraine showed increasing adult representation in the overall affected
population (
4
). Six studies involved schoolchildren; the remaining studies involved refugees, homeless
persons, and the general population.
Data from Africa, with the exception of 1 study in South Africa, were derived from
Egypt. Prevalence varied from 0% to 58.9% and was higher in females. The study in
South Africa (
5
) challenges the generally accepted concept that head lice infestation refers to lower
socioeconomic status; of 2 schools, 1 in a low socioeconomic status area, populated
by black students only, and the other in a high socioeconomic status area, populated
by students of various races, head lice infestation was found only in the second school,
solely among white pupils. Of 6 studies in Egypt, 4 involved diverse populations:
urban poor preschool children, orphanage children, and the general population.
Most studies in the Americas were conducted in Brazil, although we also found data
from the United States, Cuba, and Argentina. Prevalence varied from 3.6% to 61.4%
and was higher in females. Of 7 studies, 4 involved populations other than schoolchildren
to some extent: urban slum residents, fishing community residents, adolescents and
adults sampled randomly from the general population, elderly nursing home residents,
and persons living with repeatedly infested children. A recent study in Brazil (
6
) noted that prevalence rates determined by visual inspection are twice that of rates
determined by hair analysis.
Only 1 study has been performed in Oceania. This study in Australia reported prevalence
of 13% and that girls were more likely to have active infection.
Our review shows that pediculosis capitis is widespread throughout the world and does
not discriminate on socioeconomic status grounds. The traditional perception of head
lice as a parasitosis exclusively associated with schoolchildren of low socioeconomic
status is challenged by some of the reports (Technical Appendix).
Most studies underestimate overall prevalence by assessing it in a specific timeframe;
to the contrary, head lice infestation is a dynamic process that can spread hypergeometrically
in closed environments such as schools and in the community (
7
). The point-prevalence reported by Heukelbach et al (
8
) may represent a more accurate indicator.
Although socioeconomic status seems to be an indicator of the magnitude of lice infestation,
more specific determinants are the dynamic processes of hygienic status and overcrowding.
A recent study in Turkey compared 2 neighboring villages with different socioeconomic
status. The only factor that was statistically significantly related to pediculosis
capitis was size of the household; >6 inhabitants was associated with increased prevalence
(
9
).
Another parameter that may indirectly influence overall prevalence and account for
the leveling of the prevalence gradient between rich and poor is awareness of head
lice and preventive and therapeutic practices. A study in Australia showed that although
parents prefer to play a major role in prevention and treatment, they may lack insight
into recent advances and dilemmas regarding these measures (
10
).
Variations in reported prevalence were found even in data from the same country. These
differences can result from surveys being conducted during different seasons, various
examination techniques, reporting of active infestation or presence of nits, and potential
introduction of effective pediculicides.
Although head lice account for a substantial number of missed schooldays in children,
among others, it is surprising that pediculosis capitis is not monitored and prevalence
is not regularly reported. Although we cannot extinguish the parasite, effective monitoring
and planning will enable us to limit the prevalence and distribution of this parasitosis.
Supplementary Material
Technical Appendix
Worldwide prevalence of head lice infestation*