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From eradication to resistance: five continuing concerns about pediculosis.

The medical term for infestation of head lice -- pediculosis -- refers to the six-legged progenitor of the condition, Pediculus humanus capitis. Understanding the nature of this tiny pest suggests how to prevent its spread. The gray-white to red or black wingless insect is 2 to 4 mm long, approximately the size of a sesame seed. Commonly, no more than 12 to 24 head lice infest a child at any one time.[1] The adult female attaches 3 to 10 fertilized eggs, or nits, per day to the bases of hair shafts. Incubated at normal body temperature, these nits hatch within 10 to 12 days. They mature through three nymphal stages in less than 2 weeks, becoming adult lice capable of surviving up to 30 days. Without a human host, however, they rarely survive longer than 36 hours.[2,3]

Fortunately, head lice generally can be eradicated with non-prescription pyrethroid-based shampoos, lotions, or rinses. Active ingredients in these products include pyrethrins (also known as pyrethrum extract) with piperonyl butoxide and permethrin. Resistance to these well-tolerated pediculicides has not been documented in the United States.[3] Nevertheless, despite intensive screening and eradication efforts in this sophisticated medical era, the reported incidence of head louse infestation is increasing.[1,4] Over $100 million is spent annually on attempts to eradicate this exclusively human parasite. No compulsory national reporting system exists for pediculosis, but outbreaks frequently are reported among schoolchildren. During epidemics, up to 20% of children in a school may be infested.[1,5,6]

The school nurse deals with head lice on two levels. On the individual and school levels, the nurse's responsibility involves diagnosing and managing individual cases and classroom or school outbreaks. But the nurse also has a larger responsibility to the community. On this second level, the public health level, the nurse is responsible for educating the public so that transmission and reinfestation can be reduced. In the case of an outbreak, the nurse is responsible for notifying appropriate officials. Awareness of the local and state guidelines for control of head lice is also the nurse's responsibility.

This article addresses five major concerns that govern a school nurse's thinking in managing head louse infestations (Table 1).
Table 1
Concerns of the School Nurse in Managing Infestations of Head Lice

1. Dispelling misconceptions about head lice.

2. Ensuring that infestations are not missed.

3. Ensuring that parents understand the instructions for
effective treatment.

4. Educating the community on the correct usage of
pediculicides so as not to foster resistance.

5. Reducing the spread of infestations.


Head lice have plagued humankind for at least 5,000 years. Lice and their eggs were mummified with the ancient Egyptian nobility upon whom they dwelled,[7] and lice and eggs have been recovered from 2,000-year-old delousing combs excavated from the Judean Desert[8] Since those early days, misconceptions have surrounded this tiny, human parasite. As the pivotal health-care professional involved in school-associated cases and outbreaks of head lice, the school nurse is aware that misconceptions can hinder eradication and promote spread. Part of the nurse's job, therefore, is to dispel myths.

Myths About the Source of Head Lice

Before the introduction of the microscope, lice were believed to form by spontaneous generation from dirt, disease, or sweat.[7] Although 19th century scientific advances clarified the genesis of head lice, many educated people still equate lice with poor personal hygiene. Shame, disgust, and embarrassment[1] can lead to silence about an infestation, ensuring adequate time for the lice to establish their territory and to infest new hosts.[9] For this reason, public health workers continually advocate openness as the key to quelling an outbreak of head lice.[10]

The mode of lice transmission is commonly misunderstood. Lice cannot jump like fleas, and because they are wingless, lice cannot fly.[11] Instead, lice are passed from one person to another by head-to-head contact, for example, during an embrace. Another mode of transmission involves sharing items that come into contact with the head, including hats, helmets, brushes, headphones, and ribbons. Sharing beds, pillows, and toilet articles also enables transmission.[1] Lice may fall from their host to carpeting, household furniture, theater chairs, and linens. People coming into contact with these items may subsequently become infested.[11]

Myths About Who Gets Head Lice

Head lice seek any human host. They desire food, warmth, and shelter[9] and settle for the first opportunity that comes along. Still, people of higher socioeconomic class may believe they are unlikely candidates for infestation. This erroneous belief jeopardizes prompt treatment and encourages further spread. In fact, louse infestations correlate poorly with personal hygiene, and good personal hygiene cannot prevent infestation. Studies indicate that lice may prefer a clean head of hair to a dirty one.[10] However, combined with overcrowding, poor hygiene does enhance transmission.[1,12]

Many people assume that if they keep reasonable standards of cleanliness, they cannot be infested by head lice. As a result, they let their guard down -- even when they might have been in contact with an infested person. Further, they find comfort in feeling no immediate symptoms. This is another common misconception: A person will sense immediately that he or she is infested. On the contrary, though the louse inserts its mouthparts into the scalp and injects an anticoagulant to keep the blood flowing freely, the feeding process causes no sensation for the host.[13] Most people gradually become sensitized over several weeks, and then the bites begin to itch. Some asymptomatic carriers endure as many as 100,000 louse bites before they start itching, a process that can take three to eight months.[14]

Effect of Misconceptions on School Policy

Increasingly, schools are incorporating a "no nit" policy. Children must be free of all nits as well as lice after treatment before they are allowed to return to school.[11] This policy has some rationale, because up to 32% of nits hatch following treatment with a pediculicidal product. Studies suggest that nits differ in permeability according to their stage of development or that unborn nymphs differ in susceptibility at different growth stages.[15] One cannot distinguish a live nit from a dead one by unassisted visual examination. A no-nit policy encourages thorough nit removal concomitant with pediculicide treatment. Nits that appear on a head previously free of nits provide evidence of a new infestation, rather than rediscovery of an old case. Nit removal also discourages over-treatment and expedites screening.[4] Yet, a no-nit policy may provide a false sense of security. Just because no nits are seen in a routine examination does not guarantee that no nits are present.


Setting Screening Policies

Head lice awareness is a cooperative endeavor, involving both parents and school personnel. Public notification at the start of the school year can encourage parents to he especially vigilant at that time. Parents should also be encouraged to report infestations to the school rather than maintaining secrecy.

Some experts recommend three formal screenings during the school year: the first, during the initial week when school resumes session; the next screening should occur immediately after Christmas vacation; and the third screening should occur during the last week of school.

During summer vacation, parents should be aware of what to look for, especially if their child has a history of infestation.[4] Yet excessive screening should be avoided so that infestation does not appear to be a serious threat rather than simply a nuisance. Louse infestation is traumatic for children and parents alike, so it is incumbent upon school personnel to avoid overreaction and never to assign blame to the child.[16]

How to Diagnose

Head checks should involve more than a cursory glance at the hair. In addition to inspecting the scalp at the crown of the head, the inspector should examine behind the ears and the nape of the neck with a magnifying glass, looking for both nits and live lice.[16] Nits are silvery white, glistening, one-millimeter long teardrop-shaped eggs that adhere firmly to the hair shaft, generally near the scalp. Live lice are usually present but are well-camouflaged and move quickly from the light.[17]

Lice nits can be confused with dandruff. The diagnostic factor is how easily the suspected material can be removed from the hair. Nits are not easily combed from the hair because they are cemented to the hair shaft.[1]


Helping Parents Treat Infestations

Although pediculosis is a community problem, responsibility for elimination of lice ultimately rests with parents. Similarly, prevention begins in the home with parents as the first line of defense.[18]

School nurses can assist parents in learning effective nit removal techniques. Most parents are anxious to get rid of the infestation and eager to comply with recommendations. However, the nurse must remember that for many parents, lice removal is far down on the list of problems with which they have to cope. In such families, the nurse's job starts with motivating the parents to take an interest in the eradication process, for the good of the community as well as for the good of their own family. To encourage compliance from parents, the nurse may find it useful to request the return of the empty pediculicide bottle as proof of treatment.

When head lice are found, the school nurse is often the person who informs the parents and explains the importance of administering pediculicides. Since treatment failure often stems from poor technique,[11] instructions on how to use pediculicides also should be provided at this time. Written protocols are strongly encouraged to convey instructions that at first seem foreign, complicated, and illogical. Proper use is important not only to ensure eradication, but also for safety's sake. Preparations containing lindane may have neurotoxic effects,[19] other pediculicides may cause allergic and local reactions. The school nurse also should inform pregnant and nursing mothers that it is prudent to err on the side of caution and consult their health care provider before using pediculicides. This caution is also true for children under age two.[12]

Pediculicides neither kill all the nits nor cause them to fall off. Without the right equipment, removing all nits and lice could take up to nine hours for one long-haired child.[7] However, specially designed egg-removal combs supplied with commercial products make the process faster and more effective. A number of auxiliary nit-removal measures have been advocated. A mixture of 50% vinegar and 50% water applied to the hair for an hour before attempting to remove the nits may help loosen the cement holding them in place, but parents must be warned that this mixture will not kill lice.[20] Other authors dispute the ability of the vinegar solution to assist in removal of nits.[3]

Whether hair should be wet or dry during combing is debatable. Combing wet hair is easier, but the comb may slip through so easily that nits are not snagged. As for working with dry hair, children may not tolerate the discomfort of combing nits from hair that is totally dry. Optimally, hair should be slightly damp when combing out nits.[11] Additionally, use of a conditioner may be beneficial in the combing of the hair.

Parents should be told to comb and separate hair into four sections with a regular comb before using a nit comb. One section at a time is combed in the following manner: a one-half inch piece of hair is lifted in one hand, then combed with a nit comb from the scalp all the way down to the ends of the hair with the other. The nit glue grips in such a way that the nits cannot be shaken loose. Working with small amounts of hair helps prevent overlooking nits. The small section of hair that has been combed is then pinned back. Nits and hair containing nits should be wiped from the comb with a tissue and the tissue should be sealed in a plastic bag to prevent reinfestation. This process is continued until all four sections have been combed. The hair is then rinsed with warm water.[21] Care should be taken to ensure that nits do not fall onto clothing or towels that could then become a source of transmission.

Types of Medications

Non-prescription pediculicide shampoos used in North America are available in several formulations. The school nurse should explain to parents that they must carefully follow the instructions that come with the particular product that they purchase. Pyrethrin containing products (eg, RID[R]) should be applied to dry hair. Applying pediculicides to wet hair results in an immediate dilution 15 to 150 times less than the original concentration.[7] In addition, pyrethrin-based products are designed to be totally rinsed away, leaving no residue. They are then reapplied in seven to 10 days to eradicate the lice that hatch out from any viable nits that remain. Permethrin-containing products (eg, NIX[R]) are rinses designed to leave a residue, with the rationale that so doing will kill emerging nymphs as they hatch from the nits.[7]

One concern for parents, however, is the presence of a pesticide residue for several weeks. Another potential problem of leaving a residue is the possibility that low drug concentrations will serve to select for resistant strains of lice.[6,7] Suggestions that resistance among head lice to 1% permethrin may be on the increase prompted the recommendation that a higher concentration of the agent (ie, 5% permethrin) needs be applied to dry (not wet) hair and left on for prolonged periods in recalcitrant cases of pediculosis.[22] This use is not an approved indication. Parents also should be warned that towels used for drying hair before applying a pediculicide rinse should be handled with care -- they are contaminated.

Both pyrethrin-based and permethrin-based pediculicides, when used as directed, can completely eradicate lice by Day 7 or Day 14 after initial treatment (Table 2).[23] The combs included in the packages differ somewhat in design, but a controlled study indicated that the mean combing time per nit removed is comparable for both combs.[23]


Lindane (formerly distributed under the brand name Kwell[C], an insecticide related to DDT), is available by prescription as a I% shampoo. Overuse or accidental ingestion can lead to central nervous system toxicity, including seizures. The Food and Drug Administration recommends lindane not be used as a first treatment but be reserved for patients who have failed to respond to or are intolerant of other pediculicides.[19] This product is contraindicated in patients with known seizure disorders.[24]

Discouraging, Use of Home Remedies

Parents should be discouraged from using unconventional treatments for lice. Some people erroneously believe that washing the hair with plenty of water will drown the lice. On the contrary, the washing process itself can spread lice by transferring them to the towels used to dry the hair, making the towel a lice vector.[16]

Treatments such as kerosene, margarine, Vaseline[R], dog shampoo, pine oil, vinegar, and vinegar and alcohol are ineffective and may be dangerous.[25,26] Use of such ineffective remedies allows lice more time to proliferate and infest new hosts.

Explaining the Life Cycle to Encourage Compliance

Head lice depend on human blood and moderate temperatures to survive. The louse can survive temperatures between 59 [degrees] F and 100.4 [degrees] F.[17] Hatched lice are far more sensitive to treatment with pediculicides than are nits or unhatched eggs. Treatment regimens are designed to take advantage of the vulnerability of the adult. Thus, a second treatment is required for pyrethrin-based products[27] and often recommended for permethrin after seven to 10 days, when remaining viable nits reach hatching stage. Recent data would suggest that waiting the full 10 days is optimal.[3]

Decontaminating the Household

All persons coming into contact with the infested child must be informed, examined, and treated, if appropriate. Expeditious treatment avoids cycles of infestation and reinfestation between family members and acquaintances who come in frequent contact with the infested person.[27]

The house also should be cleaned to help prevent reinfestation. Clothing and linens used by the infested person should be washed in hot water and dried at a high temperature in a clothes dryer, if possible. Furniture, rugs, and bedding should be vacuumed. Combs and brushes should be soaked in a pediculicide or in hot water (at least 130 [degrees] F for 10 minutes).[21] Lice and nits usually die after five minutes of exposure to water at a temperature of 125 [degrees] F but can live for up to 30 minutes at cooler water temperatures.[28] Items that cannot be washed should be dry cleaned or sealed in a plastic bag for 14 days and then shaken vigorously outdoors. Areas where the infested person may have rested the head may be vacuumed and/or sprayed with a pediculicide spray.

Headgear such as bike or sports helmets should be thoroughly vacuumed.[21] Contrary to popular belief, pets do not have to be screened or treated. While pets can be infested by a multitude of parasites, human head lice do not infest them,[16] though pets can serve as transporters of lice.


Potential Effect of Low-Level Pediculicide Residues

Resistance to pediculicides can develop with any product but appears more likely with some than others. Resistance to organochlorines (ie, DDT, lindane), among the first preparations used to treat head lice, has been widely reported.[6]

Permethrin formulations were introduced in the late 1970s. Though initial results were excellent, resistance developed rapidly. Studying a total of 1,516 children, Israeli researchers found a fourfold increased rate of resistance to permethrin after just 30 months of use in that country.[6] Similarly, an outbreak in Czech schools, resulting in a 20% rate of infestation, was linked to a resistance that had developed with permethrin, the primary product used until then.[5]

Using antibiotic resistance as a model, researchers propose that lice exposed to sublethal pediculicide doses may survive. Over several generations, some may mutate sufficiently to become resistant to the original chemical. The Israeli researchers postulated that "the slow decay of permethrin on the hair after treatment may ... result in a significant period when lice are exposed to sublethal doses of insecticide perhaps affecting their reproduction, exerting further selection pressure for insecticide resistance."[6]

Steps to Avoid Resistance Development

Resistance occurs when the insect encounters the pediculicide and survives. Preventing resistance involves ensuring that levels of pediculicide are consistently high enough to allow no survivors. Ideally, use of pediculicides should be constrained by the same rules that govern the use of antibiotics, that is, do not use them unless the need is clear. Using the pediculicide periodically as a preventive measure is actually to the louse's advantage-it gives nearby insects time in which to develop resistance to the poison.[29]


Encourage Disclosure and Communication

Open communication is essential to limiting the spread of lice through a classroom and through the school. This process is difficult for many parents, who often feel embarrassed and even insulted when the diagnosis is made. Intentionally or not, many parents resist lice management. Follow-up, too, often fails because of the attendant embarrassment. The school nurse, by establishing a blame-free mode of communication, can encourage parents to report to the school nurse every case discovered at home. This open communication is critical to the proper treatment of exposed children and the environment and to prevention of widespread infestation and reinfestation.[17]

Teach Good Prevention Habits

The school nurse is responsible for teaching school personnel, students, and parents good prevention habits. Establishing and enforcing a no-nit policy is key to preventing outbreaks and reinfestations.[18] In addition, the school nurse should encourage children to hang coats and belongings properly in individual lockers, or at least spaced sufficiently to prevent direct contact. Mixing outerwear in piles should be discouraged. Research confirms that the incidence of infestation is higher when more than one child shares the same personal storage space.[16] Hats and masks should be excluded from dress up clothes. While good hygiene cannot actually prevent transmission, it is much easier to detect infestation on a clean than a dirty head.[17]

Educate for Proper Treatment

Properly treating infested children is the most important way to prevent spread. Elimination of louse infestation involves three steps: treatment with a pediculicide, the removal of nits, and treatment of personal articles and the environment.[18] Proper nit removal is essential, as no pediculicide is 100% ovicidal. Leaving nits in the hair can lead to misdiagnosis or reinfestation.[17]

Initiate Appropriate Follow-up Procedures

Follow-up is especially critical in cases of chronic infestation. When a child is repeatedly diagnosed with head lice, the school should inform parents that the child will be rechecked every two weeks at school until the child is clear of lice for two consecutive examinations (four weeks). This two-week check enables officials to identify new nits before the child is fully infested.[26]


The school nurse has a key responsibility in halting the spread of pediculosis. Though highly effective pediculicides are readily available, infestation control involves skillful application of knowledge, diplomacy, teaching skills, record-keeping, and follow-up.


[1.] Sanford-Driscoll M. Pharmacotherapy of head lice in children: an update. J Pediatr Health Care. 1987;1:284-287.

[2.] Chunge RN, Scott FE, Underwood JE, Zavarella KJ. A pilot study to investigate transmission of head lice. Can J Public Health. 1991;82:207-208.

[3.] Meinking T, Taplin D. Infestations. In: Schachner LA, Hansen RC, eds. Pediatric Dermatology, 2nd ed. New York, NY: Churchill Livingstons; 1995;1347-1367.

[4.] Clore ER, Longyear LA. Comprehensive pediculosis screening programs for elementary schools. J Sch Health. 1990;60:212-214.

[5.] Rupes V, Moravec J, Chmela 3, Ledvinca J, Zelenkova J. A resistance of head lice (Pediculus capitis) to permethrin in Czech Republic. Cent Eur J Public Health. 1995;3:30-32.

[6.] Mumcuoglu KY, Hemingway J, Miller J, et al. Permethrin resistance in the head louse Pediculus capitis from Israel. Med Vet Entomol. 1995;9:427-432,447.

[7.] Burgess IF. Human lice and their management. Adv Parasitol. 1995;36:271-342.

[8.] Mumcuoglu KY, Zias J. Head lice, Pediculus humanus capitis (Anoplura: Pediculidae) from hair combs excavated in Israel and dated from the first century B.C. to the eighth century A.D. J Med Entomol. 1988;25:545-547.

[9.] Mounder B. Attitude to head lice -- a more powerful force than insecticides. J R Soc Health. 1985;105:61-64.

[10.] Oliver P. Making sense of ... head lice. Nurs Times. 1994;90:34-35.

[11.] Clore ER. Dispelling the common myths about pediculosis. J Pediatr Health Care. 1989;3:28-33.

[12.] Halpern JS. Recognition and treatment of pediculosis (head lice) in the emergency department. J Emerg Nurs. 1994;20:130-133.

[13.] Kyle DR. Comparison of phenothrin shampoo and malathion lotion in the treatment of head louse infection. J R Soc Health. 1990;110:62-63.

[14.] Mounder JW. Human lice: Some basic facts and misconceptions (condensed). Bull Pan Am Health Organ. 1985; 19:194-197.

[15.] Meinking TL, Taplin D, Kalter DC, Eberie MW. Comparative efficacy of treatments for pediculosis capitis infestations. Arch Dermatol. 1986;122:267-271.

[16.] Clore ER. Keeping lice at bay: Useful tips for patients. N C Med J. 1988;49:318-319.

[17.] Sokoloff F. Identification and management of pediculosis. Nurse Pract. 1994;19:62-64.

[18.] Donnelly E, Lipkin J, Clore ER, Altschuler DZ. Pediculosis prevention and control strategies of community health and school nurses: A descriptive study. J Community Health Nurs. 1991;8:85-95.

[19.] Lindane product labels will be revised to recommend second-line use only. F-D-C Reports, Inc. April 8, 1996;58(15):T&G-1-T&G-2.

[20.] Lane AT. Scabies and head lice. Pediatr Ann. 1987;16:51-54.

[21.] Pfizer. RID: Parent's guide to eliminating lice and their eggs [abstract]. 1997.

[22.] Drugs for head lice. The Medical Letter. 1997;39:6-7.

[23.] Bainbridge CV, Neibart SI, Hassman H, et al. An evaluatorblinded comparative study of the clinical effectiveness of a pyrethrin-based pediculicide with combing vs a permethrin-based pediculicide with combing. Clin Pediatr. 1997, In press.

[24.] Manufacturer's prescribing information.

[25.] Damschen DD, Carlile JR. A hazard of lay medical treatment for lice [letter]. N Engl J Med. 1990;323:1776.

[26.] Colligan N. Rx for chronic lice problems. J Sch Health. 1991;61:242.

[27.] Mounder JW. Updated community approach to head lice. J R Soc Health. 1988;108:201-202.

[28.] Zack R. What to do if your patient has lice. RN. 1987;50:30-31.

[29.] Mounder JW. Strategic aspects of insecticide resistance in head lice. J R Soc Health. 1991;111:24-26.

Elaine Brainerd, RN, MA, CSN, School Nurse Consultant, EB Associates, and Project Manager, National Center for School Health Nursing, American Nurses Association, P.O. Box 3115, Branford, CT 06405-1715; Elizabeth Bowman is acknowledged as technical editor of this article. The writing of this article was supported by a grant from Pfizer Inc. This article was submitted July 29, 1997, and revised and accepted for publication November 24, 1997.
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Author:Brainerd, Elaine
Publication:Journal of School Health
Date:Apr 1, 1998
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