Study area
This investigation was conducted in the county of Kavar (52°43′41‶E, 29°11′32‶N at an altitude of about 1386 m above sea level) almost 45 km to the southeast of the capital city of Fars province, Shiraz, Iran. The mean annual ambient temperature was 22 °C and its mean annual ambient relative humidity was 65%. Its population was 83,883 in 2016. The study period was from Dec 2016 to Jul 2017.
Participants
Since the recruitment of all primary school students was very laborious to achieve, a representative sample of 21 female schools was selected based on the relatively high incidence of pediculosis in previous years and all their registered female students were screened and then searched for the presence of live P. h. capitis first by visual search of the hair and scalp and then by dry-combing or applying standard plastic detection combs (PDC) (Thornton and Ross Ltd., Huddersfield, UK) (Fig. 1). Visual inspection of viable head lice (nymphs and adults) was done with an X10 magnifying lens. Any head lice found by dry-combing was left in the hair to avoid bias. Combing was terminated as soon as live head lice were observed.
All participants were delivered handouts to take home so that any likely lice-infested family members could participate in free treatment, but the latter were excluded from final analyses. All relevant variables including the infestation and itching levels, hair style and length, nationality, age, settlement site and baths were recorded in an epidemiologic form. A signed informed assent form was also completed for each student in accordance with the principles of the revised Declaration of Helsinki, 2013.
Design and eligibility
This trial was a randomized controlled assessor blind trial to evaluate the efficacy of 1% permethrin (control) versus 0.2% parasidose (d-phenothrin) or 4% dimeticone in the treatment of head lice. To ensure that this trial remained assessor-blinded, the following measures were adopted. The applicators of the pediculicide treatments were prevented from getting aware of the product type by pouring liquids into blank, unmarked and serially-coded vials (25 ml). Although the products’ physical attributes (odor, fluidity, color, etc.) were different, assessor was further blinded by staff rotation and physical isolation of treatments at the sites. Care givers were requested not to divulge the treatment type to assessor. Case report form (CRF) data collection and assessment were also performed by blinded study staff (not recruited in the treatment) to avoid any product bias. Participants and their guardians were not able to find out which treatment applications they were assigned to. Data analysts were blinded to the identity of each treatment group too.
The exclusion criteria included scalp sensitivity to any one of the administered products, scalp hair and head skin disorders and damage such as burns, lesions, etc., secondary microbial infections, use of hair gels, bleach or oils, use of any drugs or medication, or pediculicide-based shampoos within the previous 4 weeks, favism (glucose 6-phosphate dehydrogenase, G6PD, deficiency) and non-compliance with the protocol. Any one of these may influence the study outcome. The inclusion criteria involved all female primary school children aged 6–13 year harboring one or more head lice using PDC following a standard protocol as set out below.
Ethics
Ethical approval was granted by Shiraz University of Medical Sciences, Vice-Chancellorship for Research and Technology, Ethics Committee (Code of Ethics: IR.SUMS.REC.1396.24). All procedures performed in this study involving human participants were conducted according to the international guidelines for clinical trials with pediculicides in agreement with the principles of the 1964 Declaration of Helsinki and its later amendments in 2013 or comparable ethical standards at the national and international levels. As participants were all below legal age, their parents or guardians signed a form giving written consent for their participation in treatment and stating that they realized the study objectives as outlined in information brochures. This study was also registered in the Iranian Registry of Clinical Trials (IRCT).
Sample size and random allocation
A sample size of about 80 infested individuals was calculated to be enough for this trial. Those eligible girls meeting the entry criteria were randomly allocated to receive one of the three designated head lice products by a computer generated list in balanced blocks of seven. Treatment assignment was performed by numbered sealed enveloped batches of seven. Extra duplicates were set aside in case of code breakage by participants. At the start of treatment, patients were treated by the next code available at the investigator’s disposal.
Interventions
Permethrin 1% crème rinse was originally supplied in 60 ml plastic bottles, parasidose (d-phenothrin) 0.2% in 150 ml bottles and dimeticone 4% lotion in 60 ml bottles. Each of these three products were applied to dry scalp using thoroughly shaken liquid and rapidly rinsing until the hair was fully saturated. The products were administered a few drops at a time, dispersing the liquid all over the hair with plastic gloves-covered fingers. To ensure complete coverage, the hair was combed with a normal wide-toothed comb to spread treatment evenly. The hair was left to dry naturally without the use of hair drier or towel drying. During treatments, permethrin, d-phenothrin, or dimeticone were left to remain in place for 20 min, 8 h, or 8 h, respectively; the hair was then washed off with water and allowed to dry naturally at the end of these periods. These treatments were repeated a week later. Each participant received the same product type as before. They were advised not to engage in any non-compliance activities such as the use of pediculicide-based shampoo at home, wet- or dry-combing, removing lice, etc. during this research trial.
Outcomes
At first screening and on post-treatment days, an indication of the level of head lice infestation was followed according to the frequency with which P. h. capitis was found on hair. Three (heavy, medium and light) infestation levels were recognized as: > 1 louse per first stroke of the PDC comb, only 1 louse per first stroke, and 1 louse only after 5–6 strokes of the comb, respectively [20].
The primary outcome measure was obliteration of infestation after fulfillment of the treatment regimen. Each patient was assessed for the presence of head lice on days 2, 6, 9 and 14 after the initial treatment using the PDC comb on dry hair in the same way in which the first screening was performed at the school. Inspections on days 2, 6, and 9 were restricted to 2–3 strokes of the comb on each section of the hair [21]. This aimed to give snapshot data of the status of infestation, since more frequent combing could be considered as extra intervention, thus confounding the results. There was no limit of PDC combing frequency on day 14. The lice-free rate or cure was thus defined as no lice after the second application of products, on days 9 and 14. Wet combing was practiced on these post-treatment days. Reinfestation was expressed as the transmission of head lice to individuals during the clinical trial. It was arbitrarily taken as when no more than 2 adult lice or third stage nymphs and no first/second stage nymphs were observed during PDC combing, on days 9 and 14.
The secondary outcome measures included the amelioration of pruritus severity, clinical pathology, and reported adverse events. The level of itching was assessed by a visual analog scale as outlined before [22]. Clinical symptoms involved the presence of erythema, eczema, and dermal weal. Adverse events like intolerable irritations included all health-related parameters, which could postpone or result from treatments.
Statistical analysis
This descriptive analytic study comprised the mean, frequency, and percentage to describe demographic variables in infested participants. Analyses were performed based on both the intention-to-treat (ITT) and the per-protocol (PP) populations. Differences in efficacy rates between different treatments were calculated by the 95% confidence interval, quantified using a normal approximation to the binomial distribution. One-way analysis of variance (ANOVA) was used to compare the numerical response data from patients. The Chi-square test was applied to compare treatment groups. The statistical package for the social sciences (SPSS) version 19 was applied to analyze the data. A P-value of less than 0.05 was considered to be statistically significant in all tests.