Is wet combing effective in children with pediculosis capitis infestation?

Dr Marc Tebruegge, Specialist Registrar, Department of Paediatric Infectious Diseases, St Mary's Hospital London, UK; marctebruegge@nhs.net

Dr Jane Runnacles, Senior House Officer, Department of Paediatric Infectious Diseases, St Mary's Hospital London, UK

A 6‐year‐old boy presents to the paediatric emergency department complaining of pruritus affecting his scalp. On examination you notice several nits attached to his hair as well as a few adult head lice. You are considering treatment with pediculocides, but his mother is rather reluctant to use “chemicals”. You consult the BNF for children, which apart from listing three classes of pediculocides – carbaryl, malathion and pyrethroids (permethrin and phenothrin) – outlines the option of using wet combing as an alternative. You wonder whether there is good evidence to support the sole use of this intervention in head lice infestation.

Structured clinical question

In a child with pediculosis capitis infestation [patient], is wet combing alone [intervention] effective in eradicating the parasites [outcome]?

Search strategy and outcome

Cochrane Library using the search terms “head lice” and “pediculosis capitis”: one relevant Cochrane review.¹ However, the article dates back to 2001.

PubMed (1950–to date/no limits set) using the search terms “head lice and combing”: 33 articles of which only five articles were relevant,^2–6 which are summarised in table 1. PubMed search using the terms “pediculosis capitis and combing”: 11 articles, all already identified. MeSH database search using the heading “lice infestations” produced no further relevant results.

Table 1 Treatment for pediculosis capitis infestation.

Citation	Study group	Study type (level of evidence)	Outcome	Key results	Comments
Roberts	74 children (aged 3–14 years)	Randomised	Presence of live	Cure rate was 38% for	Area where study was conducted
et al	randomised to wet combing	controlled trial	lice 7 days post	wet combing and 78%	known to have intermediate
(2000)2	(Bug Buster Kit) every 3–4	(level 1b)	treatment	for malathion. Cure 2.8	resistance to malathion. Only 50%
	days for 2 weeks or			times more likely with	of patients fully compliant (no
	treatment with 0.5% malathion			malathion (95% CI 1.0	significant difference between
	lotion (2 applications 7 days			to 5.2, p = 0.0006).	treatment groups). Majority of
	apart) without use of a nit				individuals in wet combing
	comb. Treatment carried out				group used treatment for ⩾14 days
	by parents at home.				(81%). No side effects observed.
Bingham	15 college students randomised	Randomised	Presence of live	Cure rate was 75% for	40% of lice collected showed
et al	to wet combing (Bug Buster	controlled trial	lice on day 14	wet combing and 43%	resistance to malathion and
(2000)3	Kit) every 3 days for	(pilot) (level 1b)	after starting	for insecticide (no	carbaryl. Drop out rate high (40%).
	2 weeks or single treatment		treatment	statistical significance
	with insecticide (permethrin*).			reached).
	First treatment was carried out
	by researcher, subsequent
	treatment by parents.
Plastow	30 children (aged 4–16 years)	Randomised	Presence of live	Cure rate was 53% for	Children in lotion arm more
et al	randomised to wet combing	controlled trial	lice on day 14	wet combing and 13%	heavily infested than in wet
(2001)4	(Bug Buster Kit) every 3 days	(level 1b)	after starting	for phenothrin (p = 0.05).	combing arm. Local resistance
	for 2 weeks or treatment with		treatment	Number needed to treat	pattern unknown. All patients
	phenothrin lotion (2			2.5 (95% CI 1.5 to 16.7)	completed the study and
	applications 7 days apart)			for wet combing. All	had full treatment as per protocol.
	without use of a nit comb.			children were cured after	No side effects reported
	Treatment was carried out by			prolonged treatment with
	nurse.			wet combing (maximum
				duration 24 days).
Vander	38 school children treated with	Cohort study/	Presence of live	Cure rate was 47% for	Further children included in the
Stichele	wet combing (sessions every 4–	poor quality	lice and/or nits on	wet combing and 64%	report had combined treatments,
et al	5 days for 2 weeks) and 25	(level 4)	day 14 after	for insecticides	alternative treatments or no
(2002)5	treated with insecticide alone.		starting treatment.	(combined figure).	treatment. Local resistance
	1% permethrine applied for 10		Inconsistent	No statistical	pattern unknown.
	min, 0.5% malathion for 12 h		definition of cure	comparison made.
	or pyrethrine for 30 min.		(varied between
	Parents chose initial		schools)
	treatment. If no cure on day 7,
	same insecticide applied again.
	If no cure at day 14 another
	substance was used.
Hill	126 children (aged 2–15 years)	Randomised	Presence of live	Cure rate was 57% for	Only 22% of participants had
et al	randomised to wet combing	controlled trial	lice 2–4 days	wet combing and 13%	pediculosis for the first time (88%
(2005)6	(Bug Buster Kit) four sessions	with high risk of	post treatment	for insecticides.	repeated infestation). Allocation
	with 3 days between sessions or	bias (level 1b−)		“Relative risk” 4.4 (95%	concealment was inadequate. Lice
	single dose treatment with 0.5%			CI 2.3 to 8.5) with wet	from participants tested by
	malathion lotion or treatment			combing when compared	molecular methods, confirmed high
	with 0.5% permethrin.			with both pediculocides	proportion of resistance against
	Treatment carried out by			combined.	pyrethroids. Study used newer
	parents at home.				version of the Bug Buster Kit.

*Information on which insecticide was used in this study kindly provided by the author (personal communication).

EMBASE database (1974–to date) using the same set of search terms as employed in the PubMed search: 24 results – no additional relevant articles identified.

TRIP database using the same set of search terms as in the PubMed search: 22 results – no further relevant article identified.

Search of multiple trials registers using the same search terms including ISRCTN, NHS, NIH and MRC: eight results – four unrelated to pediculosis, three trials investigating new pediculocides, one investigating “suffocation‐based” treatment – thus none relevant. The Cochrane Central Register of Controlled Trials using the same search terms: total of 10 references – all previously identified.

Search date: 17/02/07.

Commentary

Pediculosis capitis, an ectoparasitic infestation, remains a common problem in the paediatric population, although exact figures for the United Kingdom are currently unknown since most health authorities have abandoned routine screening in schools. However, previous reports have shown that there has been a significant increase in prevalence over the last decade.⁷ One regional study in England reported a prevalence of 2.0% and a worrying annual incidence of 37.4% in primary school children,⁸ while a more recent study from Wales established a prevalence of 8.3%.⁹ Studies from other European countries reported prevalences of between 0.8%¹⁰ and 8.9%¹¹ in the last few years.

Pediculocides, which are essentially neuroactive insecticides, are the most commonly used treatment for head lice worldwide. Malathion is an organophosphate, permethrin and phenothrin belong to the class of pyrethroids and carbaryl is a carbamate.

Several authors have reported increasing levels of resistance of Pediculus humanus capitis to a variety of pediculocides in recent years.^{6 9 12} A number of enzymatic alterations, including changes in acetylcholine esterase, esterases and glutathione‐S‐transferase, which affect the effectiveness of malathion and carbaryl have been identified. Regarding resistance to permethrin, a kdr type mechanism affecting sodium channels of the parasite has previously been reported. These changes in the parasite populations have been associated with an increase in the number of treatment failures. Ultimately, knowledge of the local resistance pattern may become vital to improve success rates.

In view of the emerging resistance to topical treatment, several research groups have explored oral forms of treatment, including ivermectin,¹³ thiabendazole¹⁴ and levamisole,¹⁵ and have reported encouraging results. Even more exciting are recent studies investigating non‐toxic so‐called “suffocation‐based” topical treatments. One study investigating dimeticone (now licensed in the UK as Hedrin 4% lotion) – a substance also used orally as treatment for infant colic – reported a 70% cure rate,¹⁶ while another study reported an impressive 96% cure rate without observing any adverse effects.¹⁷ However, these substances may require further evaluation and one has to consider that the effectiveness may be lower outside supervised study conditions.

Parents are often concerned about the prospect of using insecticides as treatment for head lice infestation in their children. Wet combing therefore appears to be an attractive alternative. Some authors have raised concerns about the labour intensity of this approach, which may result in poor compliance. However, a study by Roberts et al found that compliance in a wet combing group was not significantly different from compliance in a group which used malathion,² while Vander Stichele et al reported that wet combing was a more popular choice than treatment with insecticides when both options were offered to parents.⁵

A number of different louse and nit combs as well as kits, including the Bug Buster Kit (UK) and LiceMeister kit (US), are currently commercially available. In comparison to regular and detection combs, the combs used for treatment are finer toothed. It is generally recommended that treatment sessions are carried out every 3 days for 14 days (thus five sessions in total). Any shampoo or conditioner can be used for the purpose of wet combing, since this merely acts as a lubricant.

A Cochrane review by Dodd published in 2001 has assessed the different interventions for treating head lice.¹ The author came to the conclusion that physical control methods such as combing are inappropriate as primary treatment against head louse infection. However, this judgement was solely based on the only article related to this form of treatment published at the time.²

A wide variation of cure rates with wet combing has been reported by the five studies listed below. Roberts et al have reported a disappointing cure rate of 38%.² However, in this study an early version of the Bug Buster Kit was used and the low level of compliance (only 50%) is likely to have contributed to treatment failures. The later studies have shown more promising results with cure rates of between 47% and 75%. In the study by Hill et al, which reported that wet combing was far more effective than insecticides (57% vs 13%), the results may have been distorted by the fact that only 22% of the participants had acquired head lice for the first time and the majority of participants had undergone treatment with pediculocides prior to entering the study, which may have given rise to resistance.⁶ Nevertheless, a very similar observation was made by Plastow et al (cure rate 53% vs 13%), again suggesting that wet combing may be superior to treatment with insecticides in certain regions in view of the high failure rate with the latter.⁴ However, when considering the evidence one has to take into account that the study by Plastow et al was very small and did not include sample size calculations, while the study by Hill et al was previously criticised as seriously flawed.¹⁸ The main weakness in the latter study was inadequate allocation concealment, as the participating general practitioners were given the randomisation list. Thus, the investigators knew who was having which treatment before recruiting the patient into the study. This may have introduced considerable selection bias and ultimately altered the results. Schulz et al have previously shown that RCTs with inadequate or unclear allocation concealment yielded larger estimates of treatment effects (41% and 30%, respectively on average) than trials in which authors reported adequate concealment.¹⁹

Plastow et al reported another interesting observation, which was not part of the original study. The authors found that all patients were cured of the infestation when wet combing was employed for longer than the recommended 14 days. In one case treatment had to be continued for 24 days. However, it has to be taken into account that in this study the treatment was administered by a nurse specifically trained for this task. Thus in a real life situation, where wet combing is performed by parents who have not received prior training or supervision, this might not be as successful.

In conclusion, there is some evidence that wet combing is an effective treatment for pediculosis capitis when used correctly and consistently. However, as outlined above, the currently existing evidence has considerable limitations. A sufficiently large, well conducted randomised controlled trial with adequate randomisation process and appropriate allocation concealment would therefore be desirable.

However, wet combing it is not associated with any potential side effects and is generally preferred by parents over treatment with insecticides. In view of the rising level of resistance of Pediculus humanus capitis this method may represent a viable alternative, particularly as treatment failure does ultimately not carry the risk of having detrimental effects to the child's health.

CLINICAL BOTTOM LINE

• There is limited evidence that suggests that wet combing is an effective treatment for pediculosis capitis, although cure rates are variable. (Grade B)

• Parents prefer this treatment option over that of pediculocides. (Grade D)

• Treatment for a longer duration than the generally recommended 2 weeks may improve success rates. (Grade D)