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As there is no evidence to suggest that any insecticide is more effective than another, choice of first-line agent depends upon local resistance patterns. Local policies should be developed and followed where possible. Some areas advocate mechanical clearance as a first-line treatment. As stated earlier, there is no published scientific evidence to support this.

The formulation used may also be important (see table 1). Alcohol based insecticides are less likely to produce resistance and should be used where possible.¹⁰ Aqueous or cream rinse formulations are preferred in young children or those with eczema or asthma, but shampoos are not recommended.

Why does treatment fail?

Patients and/or parents should be encouraged to examine the head with a detector comb 2-3 days after the final application of insecticide to check treatment success. Only if live lice are present (as assessed by a healthcare professional) should treatment be considered to have failed. The presence of nits or eggs does not indicate treatment failure. Figure 2 illustrates the correct follow-up procedure.

The reason for any treatment failure should be investigated. It is only rarely caused by lice resistance to an insecticide. More common reasons include:

• initial misdiagnosis
• inadequate or incorrect application of treatment
• reinfection (often due to inadequate contact tracing)
• use of an ineffective insecticide formulation e.g. shampoo.

Contact tracing is essential to prevent reinfection. All proven cases should be treated at the same time with the same insecticide.¹ Anyone who has had head to head contact with an infected individual should be contacted and advised to examine their hair for live lice. Some people may be reluctant to do this because of the social stigma attached to admitting to having head lice. The checklist in the enclosed patient information leaflet may help ensure all contacts are considered.

Prevention of head lice

Prevention of infection is best achieved by regular detection combing and early intervention. The prophylactic use of insecticides is not recommended as this will not prevent infection, may encourage resistance and increases the risk of toxicity. Use of repellent shampoos and sprays is also not recommended.¹

Conclusion

Although infection with head lice is not dangerous, it can cause much distress. Elimination of head lice relies upon thorough tracing of close contacts and effective treatment of all proven cases. However, it is important that treatment is only given in confirmed cases, i.e. where a living, moving louse is seen or evidence of infection is examined by a healthcare professional.

Each proven case of infection should be assessed individually within a mosaic model of treatment. As there is no evidence that any insecticide is more effective than another, the choice of first-line agent depends upon local resistance patterns. Local policies should be developed and followed where possible.

There is no reliable evidence that mechanical methods of louse clearance, such as Bug Busting, are effective. These methods are not recommended as a treatment for the whole population. Although they require a high level of motivation, they may be an option in certain families who decline to use an insecticide or in whom treatment has repeatedly failed.

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