Abstract
Introduction
Head lice can only be diagnosed by finding live lice, as eggs take 7 days to hatch and may appear viable for weeks after death of the egg. Infestation may be more likely in school children, with risks increased in children with more siblings, longer hair, and of lower socioeconomic group.
Methods and outcomes
We conducted a systematic review and aimed to answer the following clinical question: What are the effects of treatments for head lice? We searched: Medline, Embase, The Cochrane Library, and other important databases up to June 2010 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).
Results
We found 26 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.
Conclusions
In this systematic review, we present information relating to the effectiveness and safety of the following interventions: benzyl alcohol, dimeticone, herbal and essential oils, insecticide combinations, isopropyl myristate, ivermectin, lindane, malathion, mechanical removal by combing ("bug busting"), oral trimethoprim–sulfamethoxazole (co-trimoxazole, TMP-SMX), permethrin, phenothrin, pyrethrum, and spinosad.
Key Points
Head lice can only be diagnosed by finding live lice, as eggs take 7 days to hatch, and may appear viable for weeks after death of the egg.
Infestation may be more likely in school children, with risks increased in children with more siblings, longer hair, or of lower socioeconomic group.
Malathion lotion may increase lice eradication compared with placebo, phenothrin, or permethrin. Current best practice is to treat with two applications 7 days apart, and to check for cure at 14 days.
Studies comparing malathion or permethrin with wet combing have given conflicting results, possibly because of varying insecticide resistance.
Oral ivermectin may be more effective at eradicating head lice than malathion in people with previous failed treatment with insecticides.
However, although tested in a clinical trial, oral ivermectin is not currently licensed for treating head lice, and generally its likely usefulness has been superseded by the introduction of physically acting chemicals that are not affected by resistance and which are generally considered safer.
Permethrin may be more effective at eradicating lice compared with placebo or lindane.
Eradication may be increased by adding trimethoprim–sulfamethoxazole (TMP-SMX, co-trimoxazole) to topical permethrin, although this increases adverse effects.
We don't know whether combinations of insecticides are beneficial compared with single agents or other treatments.
Dimeticone may be more effective at eradicating lice compared with malathion or permethrin.
Dimeticone and phenothrin have produced similar results, but this may be because of varying insecticide resistance and the formulation of phenothrin used.
We don't know whether pyrethrum is beneficial compared with other insecticides.
CAUTION: Lindane has been associated with central nervous system toxicity.
Some herbal and essential oils may be beneficial to eradicate lice compared with other treatments but this is likely to depend upon the compound(s) or extracts used.
Isopropyl myristate may be more effective at eradicating lice than permethrin.
Benzyl alcohol may be more effective at eradicating lice than placebo. However, we don't know whether benzyl alcohol is more effective than insecticides or other treatments used in routine clinical practice.
Spinosad may be more effective at eliminating lice than permethrin.
About this condition
Definition
Head lice are obligate ectoparasites of socially active humans. They infest the scalp and attach their eggs to the hair shafts. Itching, resulting from multiple bites, is not diagnostic, but may increase the index of suspicion. Eggs glued to hairs, whether hatched (nits) or unhatched, are not proof of active infection, because eggs may retain a viable appearance for weeks after death. A conclusive diagnosis can only be made by finding live lice. One observational study compared two groups of children with louse eggs but no lice at initial assessment. Over 14 days, more children with 5 or more eggs within 6 mm of the scalp developed infestations compared with those with fewer than 5 eggs. Adequate follow-up examinations using detection combing are more likely to be productive than nit removal to prevent re-infestation. Infestations are not self-limiting.
Incidence/ Prevalence
We found no studies on incidence and few recently published studies of prevalence in resource-rich countries. Anecdotal reports suggest that prevalence has increased since the early-1990s in most communities in Europe, the Americas, and Australasia. A cross-sectional study from Belgium (6169 children aged 2.5–12.0 years) found a prevalence of 8.9%. An earlier pilot study (677 children aged 3–11 years) showed that in individual schools the prevalence was as high as 19.5%. One cross-sectional study from Belgium found that head lice were significantly more common in children from families with lower socioeconomic status (OR 1.25, 95% CI 1.04 to 1.47), in children with more siblings (OR 1.2, 95% CI 1.1 to 1.3), and in children with longer hair (OR 1.20, 95% CI 1.02 to 1.43), although hair length may primarily influence the ability to detect infestation. The socioeconomic status of the family was also a significant influence on the ability to treat infestations successfully — the lower the socioeconomic status, the greater the risk of treatment failure (OR 1.70, 95% CI 1.05 to 2.70).
Aetiology/ Risk factors
Observational studies indicate that infestations occur most frequently in school children, although there is no evidence of a link with school attendance. We found no evidence that lice prefer clean hair to dirty hair.
Prognosis
The infestation is almost harmless. Sensitisation reactions to louse saliva and faeces may result in localised irritation and erythema. Secondary infection of scratches may occur. Lice have been identified as primary mechanical vectors of scalp pyoderma caused by streptococci and staphylococci usually found on the skin.
Aims of intervention
To eliminate infestation by killing or removing all head lice and their eggs.
Outcomes
Eradication rate: Treatment success is given as the percentage of people completely cleared of head lice. Adverse effects. There are no standard criteria for judging treatment success or what constitutes infestation. Trials used different methods, and in many cases the method was not reported. Few studies were pragmatic.
Methods
Clinical Evidence search and appraisal June 2010. The following databases were used to identify studies for this systematic review: Medline 1966 to May 2010, Embase 1980 to May 2010, and The Cochrane Database of Systematic Reviews 2010, Issue 2 (1966 to April 2010). An additional search within The Cochrane Library was carried out for the Database of Abstracts of Reviews of Effects (DARE) and Health Technology Assessment (HTA). We also searched for retractions of studies included in the review. Abstracts of the studies retrieved from the initial search were assessed by an information specialist. Selected studies were then sent to the contributor for additional assessment, using predetermined criteria to identify relevant studies. Study design criteria for inclusion in this review were: published systematic reviews of RCTs and RCTs in any language, at least single blinded, and containing >20 individuals of whom >80% were followed up. There was no minimum length of follow-up required to include studies. We excluded all studies described as "open", "open label", or not blinded unless blinding was impossible. The initial search was performed by the Cochrane Infectious Diseases Group at the Liverpool School of Tropical Medicine for a systematic review compiled in July 1998 (now withdrawn). We searched for each intervention versus placebo or versus each other, and reported any studies of sufficient quality that we found. We included systematic reviews of RCTs and RCTs where harms of an included intervention were studied applying the same study design criteria for inclusion as we did for benefits. In addition we use a regular surveillance protocol to capture harms alerts from organisations such as the FDA and the MHRA, which are added to the reviews as required. To aid readability of the numerical data in our reviews, we round many percentages to the nearest whole number. Readers should be aware of this when relating percentages to summary statistics such as relative risks (RRs) and odds ratios (ORs). We have performed a GRADE evaluation of the quality of evidence for interventions included in this review (see table). The categorisation of the quality of the evidence (high, moderate, low, or very low) reflects the quality of evidence available for our chosen outcomes in our defined populations of interest. These categorisations are not necessarily a reflection of the overall methodological quality of any individual study, because the Clinical Evidence population and outcome of choice may represent only a small subset of the total outcomes reported, and population included, in any individual trial. For further details of how we perform the GRADE evaluation and the scoring system we use, please see our website (www.clinicalevidence.com).
Table.
GRADE Evaluation of interventions for Head lice.
| Important outcomes | Eradication rate | ||||||||
| Studies (Participants) | Outcome | Comparison | Type of evidence | Quality | Consistency | Directness | Effect size | GRADE | Comment |
| What are the effects of treatments for head lice? | |||||||||
| 1 (119) | Eradication rate | Malathion versus placebo | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for sparse data. Directness point deducted for short follow-up (7 days) |
| 1 (193) | Eradication rate | Malathion versus phenothrin | 4 | –2 | 0 | –1 | 0 | Very low | Quality points deducted for sparse data and potential confounding of results because of parental non-compliance. Directness point deducted for short-term follow-up |
| 2 (238) | Eradication rate | Malathion versus permethrin | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for different time periods of agent versus single dose of another agent. Directness point deducted for restricted study population (isolated community exposed to agricultural pesticides) |
| 1 (72) | Eradication rate | Malathion versus mechanical removal of lice | 4 | –1 | 0 | 0 | +1 | High | Quality point deducted for sparse data. Effect-size point added for RR >2 |
| 1 (133) | Eradication rate | Malathion or permethrin versus mechanical eradication | 4 | –2 | 0 | –1 | 0 | Very low | Quality points deducted for sparse data and inadequate length of follow-up for 1 group. Directness point deducted for use of non-standard doses |
| 1 (73) | Eradication rate | Malathion versus dimeticone | 4 | –1 | 0 | 0 | 0 | Moderate | Quality point deducted for sparse data |
| 7 (726) | Eradication rate | Permethrin versus lindane | 4 | –1 | 0 | 0 | 0 | Moderate | Quality point deducted for incomplete reporting of results |
| 1 (63) | Eradication rate | Permethrin versus placebo | 4 | –1 | 0 | 0 | 0 | Moderate | Quality point deducted for sparse data |
| 1 (115) | Eradication rate | Trimethoprim–sulfamethoxazole (TMP-SMX, co-trimoxazole; oral) versus permethrin | 4 | –2 | 0 | –1 | 0 | Very low | Quality points deducted for sparse data and poor quality of follow-up. Directness point deducted for inclusion of other intervention, non-identical comparators, and non-standard doses |
| 1 (115) | Eradication rate | Trimethoprim–sulfamethoxazole (TMP-SMX, co-trimoxazole; oral) plus permethrin versus permethrin alone | 4 | –2 | 0 | –1 | 0 | Very low | Quality points deducted for sparse data and poor quality of follow-up. Directness point deducted for inclusion of other intervention, non-identical comparators, and non-standard doses |
| 1 (253) | Eradication rate | Dimeticone versus phenothrin | 4 | 0 | 0 | –1 | 0 | Moderate | Directness point deducted for uncertain generalisability of intervention |
| 1 (145) | Eradication rate | Dimeticone versus permethrin | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for sparse data and for early termination of RCT at 9 days |
| 1 (143) | Eradication rate | Herbal and essential oils versus combined insecticides | 4 | –2 | 0 | –1 | 0 | Very low | Quality points deducted for sparse data and failure to explain high withdrawal rate. Directness point deducted for uncertain generalisability of herbal product outcome |
| 1 (100) | Eradication rate | Herbal and essential oils versus permethrin | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for sparse data. Directness point deducted for unclear generalisability of the single specific herbal product |
| 1 (95) | Eradication rate | Combing plus insecticide versus insecticide alone | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for sparse data. Directness point deducted for uncertain generalisability of results. |
| 1 (30) | Eradication rate | Phenothrin versus mechanical removal of lice | 4 | –2 | 0 | –1 | 0 | Very low | Quality points deducted for sparse data and different follow-up for different groups. Directness point deducted for uncertain generalisability of intervention |
| 1 (168) | Eradication rate | Isopropyl myristate versus permethrin | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for sparse data. Directness point deducted for early termination of 1 RCT |
| 1 (60) | Eradication rate | Isopropyl myristate versus pyrethrum | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for sparse data and incomplete reporting of results |
| 1 (812) | Eradication rate | Oral ivermectin versus malathion lotion | 4 | 0 | 0 | –1 | 0 | Moderate | Directness point deducted for restricted population (only in people with failed insecticide treatment or a household contact with failed insecticide treatment) affecting generalisability beyond this group |
| 2 (250) | Eradication rate | Benzyl alcohol versus placebo | 4 | –1 | 0 | 0 | 0 | Moderate | Quality point deducted for incomplete reporting of results |
| 1 (347) | Eradication rate | Spinosad versus permethrin | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for incomplete reporting of results (percentages only) and no efficacy results for one arm of trial |
We initially allocate 4 points to evidence from RCTs, and 2 points to evidence from observational studies. To attain the final GRADE score for a given comparison, points are deducted or added from this initial score based on preset criteria relating to the categories of quality, directness, consistency, and effect size. Quality: based on issues affecting methodological rigour (e.g., incomplete reporting of results, quasi-randomisation, sparse data [<200 people in the analysis]). Consistency: based on similarity of results across studies. Directness: based on generalisability of population or outcomes. Effect size: based on magnitude of effect as measured by statistics such as relative risk, odds ratio, or hazard ratio.
Glossary
- High-quality evidence
Further research is very unlikely to change our confidence in the estimate of effect.
- Low-quality evidence
Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
- Moderate-quality evidence
Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
- Pediculicide
Any compound or material (possibly a pesticide) that kills lice. This term is used specifically in place of "insecticide" as not all pediculicides are recognised pesticides. A pediculicide is distinct from an "ovicide", which kills louse eggs, although one substance may fulfil both functions.
- Pragmatic RCT
An RCT designed to provide results that are directly applicable to normal practice (compared with explanatory trials that are intended to clarify efficacy under ideal conditions). Pragmatic RCTs recruit a population that is representative of those who are normally treated, allow normal compliance with instructions (by avoiding incentives and by using oral instructions with advice to follow manufacturers' instructions), and analyse results by "intention to treat" rather than by "on treatment" methods.
- Scalp pyoderma
Scalp pyoderma involves impetigo-like bacterial infections that result from scratching. In most cases they are caused by streptococci, with some staphylococcal involvement. Scalp pyoderma of this type is closely associated with long-term louse infestation.
- Very low-quality evidence
Any estimate of effect is very uncertain.
The information contained in this publication is intended for medical professionals. Categories presented in Clinical Evidence indicate a judgement about the strength of the evidence available to our contributors prior to publication and the relevant importance of benefit and harms. We rely on our contributors to confirm the accuracy of the information presented and to adhere to describe accepted practices. Readers should be aware that professionals in the field may have different opinions. Because of this and regular advances in medical research we strongly recommend that readers' independently verify specified treatments and drugs including manufacturers' guidance. Also, the categories do not indicate whether a particular treatment is generally appropriate or whether it is suitable for a particular individual. Ultimately it is the readers' responsibility to make their own professional judgements, so to appropriately advise and treat their patients. To the fullest extent permitted by law, BMJ Publishing Group Limited and its editors are not responsible for any losses, injury or damage caused to any person or property (including under contract, by negligence, products liability or otherwise) whether they be direct or indirect, special, incidental or consequential, resulting from the application of the information in this publication.
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