Study area and participant eligibility
The study area is located about 150 km east of Bangkok at transmission foci in Plaeng Yao District, Chachoengsao Province, eastern Thailand. Our Thai research group has already established excellent relationships with local schools because of a decade of research in this area
[28–30]. The climate consists of a rainy season from May to October followed by a long dry season. The region covers an area of 237 km2 and a population of 36,607 persons (census 2005;
http://en.wikipedia.org/wiki/Plaeng_Yao_District). There are 24 primary and secondary schools in this area, of which we will select 10 schools that have between 100–500 students who are willing to participate. All children aged 7 to 18 years old will be eligible. In order for the results from this study to be as generalisable as possible, with the exception of children with eczema or other severe underlying skin diseases, no exclusions will be made on the basis of gender, ethnic group, medical condition or physical health. Inclusion will require parents/caretakers to give informed written consent; in the case of children older than 12 years, assent will also be required. Subjects and households will be free to withdraw from participating in the study at any time without giving a reason. To ensure a high compliance rate among children in participating schools, awareness campaigns in the community and in the schools will be held. Information sessions with the school leadership, school teachers and parents will be conducted between October 2011 and May 2012 before the start of trial.
Study subjects will be enrolled between January and June 2012. The intervention/control will commence in mid-May to June 2012, at the start of the Thai school year.
Routinely used school uniforms will be collected from all consenting children and treated with a long-lasting permethrin formulation, using a factory proprietary method. The process involves coating the uniforms in a proprietary formula containing 0.52% permethrin (Insect Shield USEPA2009). The technology claims to provide 80–96.7% knockdown after 70 washes
. Enrolled children will receive either permethrin impregnated or untreated school uniforms. For schools assigned to the control group, uniforms will be collected and washed using the same methodology as those used in the treatment group, but without the impregnation process with permethrin.
School uniforms vary in form, colour and size. School uniforms include the regular school uniform, scouts uniform, sports uniform and cultural uniform. Most of the typical uniforms are short-sleeved and only cover the legs down to the knees (shorts or skirts). The variation between the schools is minimal for the uniforms, except for the cultural uniform.
A cluster-randomised, double-blinded, crossover design will be implemented. Randomisation will be by school. An individual participation rate of at least 90% within each school is anticipated. The schools will be randomised into two equal groups, with each school receiving impregnated uniforms in either the first (2012–13) or second (2013–14) annual transmission season covered by the trial.
Randomisation and blinding
There will be double-blinding: neither the children nor the investigators will know the allocation. School uniforms from Thailand will be sent to the InsectShield factory: one group will undergo washing and treatment with permethrin. The control group will only undergo washing. Both the impregnated and washed uniforms will be identified with labels indicating the child’s name, school and year, but there will be no identifiable indication as to which uniforms are actually impregnated.
All participating schools will be stratified into two by enrolment size, above and below median. Randomisation to two groups (intervention followed by control, control followed by intervention) will be carried out in Sweden. This information will be kept confidential between one epidemiologist and the impregnation facility.
Sample size for the trial will take into account likely levels of dengue incidence, as well as the considerable wide-area variation in transmission from season to season, and local area (i.e., per school) variation
. Such large potential variations are unpredictable and difficult to quantify. The advantage of the crossover school-randomised design – which can be interpreted as a cluster-randomised design in relation to individuals – is that if there are particular factors driving local area variation from year to year (such as mosquito breeding sites close to schools), those sources of variation will, to some extent, be controlled by the crossover design. This design efficiency is a considerable advantage, notwithstanding the relatively large design effect that needs to be applied to the overall sample size in recognition of the cluster randomisation and the considerable uncertainties around wide-area incidence rates from year to year.
In view of the probable large size of these variations and their inherent uncertainty, a design factor of 3 is used.
A design factor greater than unity is justified because of the school clustering effect. Unfortunately, because of the paucity of knowledge of dengue epidemiology, both in terms of year-on-year variation and its determinants in Thailand in general, and compounded by possible local variations in dengue that might occur between school locations, it is impossible to make detailed calculations of the required design effect. The choice of 3 as the design effect was therefore adopted as a conservative estimate in the absence of being able to make any better estimate.
The basic assumptions underlying the sample size for the trial are an incidence rate (symptomatic plus asymptomatic) of an average of 5% during a transmission season
, i.e. 10% over two seasons; an aim of halving incidence by using impregnated uniforms (since any smaller effect would not be of policy interest) and a dropout rate (children leaving the school, etc.) of 20%.
According to Schouten and Kester
], the overall sample size for a non-clustered crossover design can be calculated as
For comparing a 10% incidence with 5%, this amounts to an overall sample size of 508 (90% power, p = 0.05). Increasing this figure by 20% to allow for dropout takes this to 610, and allowing for 10% of children to become infected and take no further part in the trial takes this to 670. A design effect of 3 then takes the total sample size to 2,012 (i.e., 1,006 in each study arm).
Determining new dengue infections during the study period
Blood samples will be collected via venipuncture (2 ml) or finger prick (<0.2ml) from all study subjects at the beginning of the school term (June 2012) and at the end of the first study period (November 2012). Dengue IgG ELISA (with titres) will be measured at the Center of Excellence for Vectors and Vector-Borne Diseases (CVVD), Faculty of Science, Mahidol University at Salaya. The paired serum samples from each volunteer will be screened quantitatively for anti-dengue IgG antibodies by ELISA using a standardised protocol and reagents.
Passive and active surveillance for dengue and febrile episodes will be maintained throughout the study period (school term).
The parents of any child treated for a febrile episode during the study period will be asked to bring their child to the nearest health facility if the child does not show improvement within 48 h. When such study subjects report to a health facility, government nurses or doctors will treat the child following national guidelines and inform the study nurses or local public health officers stationed in the study area. Blood samples for dengue IgM and IgG and dengue PCR will be taken if there is a fever > 37.5°C. In case the health centre has no facilities for taking blood, the child will be advised to go to a centre with such facilities. The blood samples will be sent to a specified laboratory centre in Bangkok.
To enhance passive surveillance, we will also undertake active surveillance of febrile episodes. During the school term, field assistants will daily check from the school records for children who have been reported as absent for 2 days. The caretakers of those children will be contacted to find out about the reason for absenteeism. For those children who are reported to be absent because of a febrile illness, a blood sample will be taken within 4 weeks after onset of illness to check for dengue IgM. Furthermore, any laboratory data and clinical information will be collected directly from the health centre in case the child has gone to such a health centre or hospital.
Laboratory definition of dengue infection
Evidence of recent dengue virus infection
This is defined as detectable IgM dengue antibody, or positive dengue PCR and/or NS1 Antigen, as sampled from the passive and active surveillance.
Dengue virus infection during the study period
This is defined by quantitative dengue IgG ELISA, as a fourfold increase in antibody titres against any dengue virus serotype between the baseline and end of study specimens in paired sera.
Mosquito abundance in ten study schools will be measured. One BG sentinel trap per school will be randomly placed indoors at the beginning of the school day (8.30 am) and the mosquitoes will be collected at the end of the school period (3.30 pm). In addition, mosquitoes in each classroom will be collected by portable vacuum aspirators operated for 5 min per classroom. In order to determine species composition of mosquitoes around the school areas, ten ovitraps per school will be randomly placed indoors and outdoors around the school areas and will be left for 7 consecutive days before collection. Eggs collected from ovitraps will be reared to adults and the species will then be identified in the laboratory. These measurements will be taken at baseline and then every 4 weeks to compare entomological changes between the intervention and control schools.
To determine whether there is loss of efficacy against mosquitoes, throughout the entire study period five items of clothing from the ten schools will be examined monthly. This will be done using standardised WHOPES-recommended cone tests.
Using a cost-of-illness approach
, we will examine the economic impact of dengue infection in school-aged children at the household level. While considering the direct costs and indirect costs on households resulting from an illness episode, our analysis will exclude psychosocial costs that are difficult to estimate. A patient questionnaire will be administered to mothers/caretakers of children who have had a febrile illness episode. The questionnaire will document demographic and socioeconomic information of households, characteristics of the child’s illness episode (average duration of fever and illness and symptoms), health-seeking behaviour (type and setting of care received), household spending (direct medical costs and non-medical costs), work and school absenteeism (number of days lost for paid work and from school), informal care costs (hours of patient care provided by household members), and household income lost because of child’s illness episode.
The economic evaluation will include the cost-effectiveness analysis of insecticide-treated uniforms for the prevention of dengue infection based on the intervention efficacy and cost data derived from the trial. The cost-effectiveness analysis will follow standard guidelines of economic analyses and will be conducted from the societal perspective
. The intervention costs will be identified, measured and valued alongside the trial. Healthcare resource use data will come from the cost-of-illness study described above. Unit costs for ambulatory and inpatient care will be derived from national published data. Effectiveness will be measured in terms of dengue cases and DALYs averted because of the intervention. To assess the impact of uncertainty in key input variables on the cost-effectiveness results, we will undertake probabilistic uncertainty analysis using Monte Carlo simulations.
Quantitative questionnaires in randomly selected students from four schools will be used to determine the main activities of children before and after school in terms of outdoor versus indoor behaviour, types of activities undertaken before and after school, and whether the school uniform is worn after school and for how long, including how the school uniforms are treated (washed and dried) between use. Furthermore, qualitative studies will be used in a small number of randomly selected students to evaluate the washing habits at home. Home visits will be done and key informant interviews conducted with those household members in charge of laundry washing. The purpose is to describe the main methods of washing, drying and ironing.
Movement of children will be assessed using brief questionnaires to estimate the time at risk and usage of the allocated uniforms.
Spatial clustering analysis of dengue infections will be carried out to determine transmission foci using geographical information systems (GIS). Locations of schools and study participant home residences will be mapped. Dengue cases will be reported geographically to detect potential hot spots or spatial transmission patterns.
The primary endpoint is a comparison of the incidence rates of laboratory-confirmed dengue infections per person-time exposed up to failure (i.e. dengue infection) or censoring (i.e. moving away) between the intervention and control groups.
There are no apparent risks to the safety of individuals or communities in this study. Due to its low toxicity and long-lasting efficacy, permethrin is one of the most commonly used insecticides in impregnated clothing. Low irritancy and odour also add to the popularity of permethrin-impregnated clothing
. Permethrin-treated uniforms have been fully evaluated by multiple governments for use in military uniforms, for example in the US, Germany and France
[21, 36]. Even though there is some absorption of the permethrin through the skin, the amount absorbed is well below the acceptable daily intake, and health side effects are not expected
[13, 37, 38]. Insect Shield has met all health requirements for approval by the United States Environmental Protection Agency (USEPA) and has maintained these health standards since 2006 (Insect Shield USEPA, 2009). They are approved for vector control, and the products will be used in compliance with their recommended use and guidelines.
Teachers will document any skin irritations initially every 2 weeks, then every 4 weeks during the study period. Should skin irritations occur, the students will be sent to the study medical clinics for further documentation by trained personnel. In the case that a participant develops a serious adverse event (SAE) during the course of the study, this will be captured in the case report form. In case of an SAE, the study physician will record and manage the SAE in accordance with Good Clinical Practice (GCP). Excessive clustering of SAE by school will be reported to the study’s Data Monitoring and Safety Committee (IDMC). A determination by the IDMC that there is a potential harm to participants or the environment caused by the interventions will result in discontinuation of the study.
If an individual wants to terminate his/her participation, no further follow-up will be performed. In the case of a study child leaving during year 1, they will be replaced in year 2 of the study (May-June 2013). There will be no replacement during the surveillance period either year. If a school opts out of the study before July in either year, replacement by a neighbouring school will be considered.
This study is conducted in accordance with the principles set forth in the International Conference on Harmonization Tripartite Guideline of Good Clinical Practice and the Declaration of Helsinki. The study was approved by the Thai Ethics Review Board. Using a crossover, school-randomised design means that every individual will be equally exposed to the risks of dengue infection and to possible benefits of the intervention, taken over the entire trail period. Serious adverse effects of wearing the impregnated clothes will be reported to the Ethics Review Board within 24 h.