Head lice infestations affect millions of people inthe United States. Children become infested moreoften than adults and account for the largest percentageof infestations. Head lice have not beenshown to transfer disease, and they are not associatedwith serious morbidity. The most common effectof lice infestation is pruritus of the scalp with occasionalcutaneous infection caused by scratching.Nevertheless, many schools have "no-nit" policies,which require the dismissal of children from schoolif nits or lice are found. These policies are ineffectivein preventing infestations and result in many misseddays of school.
Lice infestations are most effectively managedwith pediculicides. Pyrethroids are the mainstay ofover-the-counter products. Prescription pediculicidesinclude OVIDE® (malathion) Lotion, 0.5% andlindane (formerly marketed as Kwell). Resistance topyrethroids due to misuse and overuse has beendocumented. Lindane resistance also has beenreported, and serious safety issues about lindanehave been raised by the Food and DrugAdministration. Lindane labeling now includeswarnings and several restrictions in its use.Malathion is not associated with major systemicsafety issues or the development of resistance withinthe United States.
A contributor to pediculicide resistance is misdiagnosisof lice infestations. Survey data reveal frequentmisdiagnosis of infestations in children whodo not have live lice. Physicians generally are morelikely to misdiagnose infestations than non-healthcareproviders. Misdiagnosis contributes to resistanceby causing overuse, and consequently overexposure,of pediculicides. These agents should be used only iflive lice or viable nits are discovered.
Head lice infestations generally do not contributeto health risks for individuals or the public. The mostserious consequence is the social cost of missedschool days and the associated cost of lost productivityand wages of parents who must care for childrensent home from school. Better diagnosis, moreappropriate use of pediculicides, and elimination ofno-nit policies will improve the overall managementof head lice infestations.
(Am J Manag Care. 2004;10:S260-S263)
Incidence and Prevalence of Head Lice
Head lice infestations () occur worldwide. Although more commonin developing countries, head lice infestationsare endemic in the United States,particularly among school-aged children.1Approximately 6 million to 12 million infestationsoccur per year in the United Statesamong children 3 to 12 years of age.2 Thesefigures are estimates, however, because patientsmay self-treat, so many cases of infestationare never disclosed to health officials.
The beginning of the school year is oftenassociated with lice infestations amongchildren. In fact, infestations take placethroughout the year, and peak activityoccurs during the summer.3 In warm temperaturesor environments, lice lay moreeggs than in cooler temperatures and aregenerally more active. Children who interactwith one another during warm weather maytransfer lice to siblings and playmates.Infestations are more commonly spreadwithin families than within schools becauseof close personal contact and shared brushesand combs.3,4 "Epidemics" may seem tooccur in September because school nursesor other school staff often screen for lice asa means of controlling the spread of infestations,and children who are infested maytransfer lice to school playmates duringclose contact. In reality, infestations do notbegin or end with the school year. The perceivedincrease in lice activity in the fallmay have more to do with monitoring practicesthan with actual numbers of lice.5
A common misconception is that infestationsoccur more frequently among lowerincome populations, but head lice are foundamong all socioeconomic groups.2 Infestationsalso occur among most ethnic groupsin the United States, although AfricanAmericans are less likely to be affected. Thislower prevalence rate is thought to be theresult of differences in the structure of thehair shaft, which may be oval shaped andtherefore more difficult for a louse to grasp.2,3There are, however, lice that have adapted tothe hair type commonly found amongAfrican Americans, so the incidence in thispopulation is increasing.3 In the UnitedStates, girls are somewhat more likely thanboys to become infested, perhaps because ofthe sharing of brushes and combs.1,3 There isdisagreement in the reported literature aboutwhether long hair increases the likelihood ofbecoming infested,6 but increased risk ofinfestation among children with long hairmay be again associated with gender differencesand the practice of sharing groomingitems.1,3 Short hair does not prevent infestationwith head lice.6 Complete shaving of thehead generally does eliminate lice and preventsreinfestation but is rarely an appropriatemeasure to take in response toinfestation.
Pathophysiology and Life Cycleof the Head Louse
Pediculus humanus capitis
is an ectoparasitethat lives only on human hosts. No animalhosts are associated with head lice. Licesurvive by feeding on blood drawn from thehost's scalp. Lice may feed and mate asoften as every 4 hours and may do bothconcurrently.3
A female louse lays an average of 5 to 10eggs per day. Lice prefer warm environments,so in cool or temperate climates licelay eggs close to the scalp and may lay fewereggs. In warmer climates, however, lice maylay eggs farther away from the scalp and maylay more eggs. Once hatched, lice can survivefor up to 30 days. Despite the largenumber of eggs that can be laid and the life-spanof the louse, the average infested hosthas only approximately 20 active head liceat one time. Hosts who are not able to groomthemselves may have more.3
Females, at an average length of 2.4 to 3.3mm, are slightly larger than males, whichrange from 2.1 to 2.6 mm. Eggs, or nits, arevery small and are silver-gray in color. Shellsleft behind once the nit emerges tend to dryup but may be mistaken for live lice or viablenits. Adult lice can adapt to the color of theirsurroundings. The small size of lice and theirability to camouflage themselves can makethem difficult to see.
Lice infestations are spread primarily bydirect head-to-head contact. Less commonly,fomites such as hats, scarves, and brushesmay transfer lice from one host toanother.1-3 However, lice cannot survive forlong when away from the host, so transfer byfomite must occur relatively quickly. A lousethat has fallen from the host onto anothersurface, such as the floor, probably will notsurvive to infest a new host. It is a commonbut incorrect belief that lice jump from headto head. Lice cannot jump, fly, or crawl longdistances. Close, personal contact generallyis required for an infestation to spread.2,3
Effects on the Host
When lice feed, they inject saliva into thehost to promote vasodilation. The saliva mayproduce an immune response in the host,leading to pruritus.1,3 A louse's fecal materialmay also contribute to scalp irritation.Scratching an itchy scalp occasionally causescutaneous scalp infection, but infestationgenerally is not associated with serious morbidity.1,2 In the United States, the primaryconsequence of head lice infestation issocial, affecting relationships or attendanceat school or work. It is accurate to say thatthe greatest "morbidity" associated with liceinfestation is missed school days because of"no-nit" policies. These policies, which areintended to control in-school infestations,prohibit attendance by children who haveevidence of head lice. Children who attendschools with no-nit policies may miss severaldays of school per year. In addition toschool absences, children may be scornedby classmates because of the stigmaattached to lice infestation in the UnitedStates. Although socially embarrassing, requiredabsence from school adds to theburden of children who are infested by isolatingthem and causing them to miss valuableclassroom experience. (This topic willbe discussed in more detail in the article inthis supplement titled, "Treating and ManagingHead Lice: The School Nurse Perspective.")Medical and nursing professionalsshould resist attempts to exclude childrenfrom school and work with policy makers tocontrol infestations with less negativeimpact on individually affected students.
Pyrethroids are the mainstay of over-the-counterpediculicides and include productscontaining permethrin 1% (eg, Nix®) and synergizedpyrethrins (eg, A-200®, RID®, Pronto,and R&C® shampoo). Pyrethrins are "synergized"by the addition of piperonyl butoxide,which enhances the pediculicide effects ofpyrethrins. Prescription pediculicides includeOVIDE® (malathion) Lotion, 0.5% andlindane (formerly marketed as Kwell).
Resistance is a primary concern in selectingan appropriate treatment. Documentedresistance to pyrethroids and lindane is wellestablished.7 Resistance to one type ofpyrethroid product probably indicates resistanceto any product in the class. Despiteincreasing resistance, these products are stillwidely used because they are available over-the-counter and are therefore easy to obtainfor at-home treatment. Among prescriptionproducts, lindane resistance has also beennoted.7 In addition, the safety of lindane hasbeen called into question by the Food andDrug Administration, which now recommendsits use only in certain patients forwhom other pediculicides have failed.8 Givenits reduced efficacy because of resistantlice, as well as safety concerns, lindane isnot recommended as first-line treatment.Malathion, another topical prescription pediculicide,is not associated with systemic safetyissues or the development of resistancewithin the United States.7
Generally accepted criteria for documentingresistance are still under discussion.Some practitioners state that if a product hasbeen correctly used but lice are still present2 to 3 days later, resistance is likely to haveoccurred. Topical pediculicides should bereapplied if live lice are seen 7 to 10 daysafter the first applications.2 If lice are presentafter 2 correctly applied treatments, resistanceto the pediculicide is certain.
Another significant issue associated withtreatment is misdiagnosis. According toresearch by Pollack et al, misdiagnosis oflice infestation occurs frequently, causinginappropriate quarantine and treatment ofchildren who are not infested and under-treatmentof children with active infestations.9 In a study of diagnostic accuracyamong children suspected of head lice infestation,misdiagnosis occurred becausescreeners often could not distinguish live,viable lice from other materials, such as dandruff,epidermal matter, and other debris.Presence of these materials frequentlyresulted in misdiagnosis of active infestation;conversely, screeners often overlookedlive lice among children who did have activeinfestations. The result was that childrenwho were not infested were excluded fromschool more often than children who hadlive infestations. Interestingly, physiciandiagnosis of lice infestation was least accurate,although nonhealthcare providers alsofrequently misdiagnosed the condition.School nurses were most accurate but failedto distinguish live from extinct infestations.Researchers concluded that misdiagnosis iscommon, that treatment should be recommendedonly with the discovery of live liceor viable nits, and that no-nit policies shouldbe reevaluated because so many childrenare inappropriately excluded from school.9
Resistance and misdiagnosis have beenshown to result in unnecessary and inappropriatetreatment with pediculicides. Asidefrom the social effects of inappropriate treatment,there are cost consequences. Accurateestimates of the total costs of treatment in theUnited States are difficult to obtain, but informalestimates based on the standard cost ofover-the-counter pediculicides used twicewould be approximately $120 million for thelower range of 6 million infestations peryear.10 Higher estimates of infestations andthe need for repetitive application when treatmentsfail because of resistance substantiallyincrease the total costs of eradicating headlice. Added to the direct costs of pediculicidesare the indirect costs of lost productivitybecause of missed school and work days.More discussion of direct and indirect costs oftreatments is included in the article in thissupplement titled, "Head Lice TreatmentCosts and the Impact on Managed Care."
Lice infestation is viewed as a sociallyrepugnant condition, but it is not associatedwith significant morbidity except for pruritus and occasional pyoderma. Among children,who are most likely to become infested,the primary negative effect of liceinfestation is absence from school. Well-meaningbut misguided school policies thatexclude children with lice infestation shouldbe revised or eliminated. Research hasdemonstrated that misdiagnosis of lice infestationis common, and a significant numberof children who are sent home do not haveactive infestations.9 This, coupled withresistance to commonly used pyrethroidpediculicides, results in inappropriate andunnecessary head lice treatment commonlyoccurring among school-aged children.
The effects of misdiagnosis and resistanceare costly in terms of direct and indirect coststo society. Direct costs include costs of treatment,which may be repeated several times iflice are resistant. Indirect costs are evenmore substantial, including missed days fromschool and parental work days missed to carefor a child who has been sent home fromschool. Recommendations for improvingtreatment include increasing the accuracy ofdiagnosis, treating only those children whohave confirmed, active infestations, resistingno-nit policies, and using pediculicides properlyto decrease overexposure to children andthe possibility of promoting treatment-resistantlice. Ultimately, the development of newpediculicides will be needed as resistanceincreases. These topics will be described inmore detail in this supplement.
1. Recommendations for the treatment of pediculosiscapitis (head lice) in children. University of Texas atAustin, School of Nursing, Family Nurse PractitionerProgram. 2002. Available at: http://www.guideline.gov/guidelines/FTNGC-2451.html. Accessed on June 17,2004.
2. Frankowski BL, Weiner LB; Committee on SchoolHealth the Committee on Infectious Diseases.American Academy of Pediatrics. Head lice. 2002;110:638-643.
3. Meinking T, Taplin D. Infestations. In: 3rd ed. Schachner LA, Hansen RC, eds.Edinburgh:Mosby; 2003:1141-1180.
4. Hansen RC. Guidelines for the treatment of resistantpediculosis. (suppl). Montvale,NJ: Medical Economics; 2000:4-10.
5. Pollack J. Head lice information. Harvard School ofPublic Health. Available at: http://www.hsph.harvard.edu/headlice.html. Accessed on June 17, 2004.
Can J Public Health.
6. Chunge RN, Scott FE, Underwood JE, Zavarella KJ. Areview of the epidemiology, public health importance,treatment and control of head lice. 1991;82:196-200.
7. Meinking TL, Serrano L, Hard B, et al. Comparativein vitro pediculicidal efficacy of treatments in a resistanthead lice population in the United States. 2002;138:220-224.
8. FDA Public Health Advisory: Safety of TopicalLindane Products for the Treatment of Scabies and Lice.Center for Drug Evaluation and Research. Available at:http://www.fda.gov/cder/drug/infopage/lindane/default.htm. Accessed on June 17, 2004.
Pediatr Infect Dis J
9. Pollack RJ, Kiszewski AE, Spielman A. Overdiagnosisand consequent mismanagement of head louse infestationin North America. . 2000;19:689-693.
Pediculus humanus capitis
10. Hansen RC, O'Haver J. Economic considerationsassociated with infestation. 2004;43:523-528.