Evidence based community mobilization for dengue prevention in Nicaragua and Mexico (Camino Verde, the Green Way): cluster randomized controlled trial

Patient involvement

Patients who had previously had dengue and their families were not involved in setting the research question or the outcome measures, but they were they intimately involved in design and implementation of the intervention. Patients and their families were also central to dissemination of the baseline information, which helped to motivate community involvement during and beyond the study. 

Participants

Participants were all residents in a stratified last stage random sample of enumeration areas17 (the geographic area canvassed by one census representative) from the latest censuses, with 60 clusters in Nicaragua and 90 in Mexico. We included all children aged 3-9 whose parents consented to them providing a saliva sample. The Guerrero sample covered three coastal regions (Costa Grande, Acapulco, and Costa Chica), stratified for population size and dengue prevention programs. The Nicaraguan sample came from the capital city of Managua, where a quarter of the national population lives. This sampling frame excluded 17 wealthy enumeration areas, where residents typically make private security arrangements and do not participate in public health initiatives for the popular neighborhoods. Table A in appendix 1 shows baseline demographic, infrastructural, and socioeconomic factors that could influence dengue transmission.

Before the baseline surveys, we received permission from the mayoral office and community leaders. Individual consent was also read to every respondent, all of whom were told that they were free to decline to answer any question they opted not to answer. Parents gave individual consent for each child who contributed saliva samples. The interventions started with requesting permission from community leaders.

Interventions

Before randomization, interviewers returned entomology results to all households and individual serology results to parents of the children who had provided saliva samples for serological testing. All clusters continued the official government dengue control programs (monthly deposits of temephos sachets in water storage of all households and space spraying), and all participated in a baseline and follow-up trial survey.

Interventions covered self identified neighborhoods and were not confined to the 140 household impact assessment clusters within them. All intervention communities followed the same intervention protocol, initiating the community engagement through three protocol steps:

• The researchers asked permission from community leaders and engaged them in discussion of baseline evidence

• Facilitators convened and ran intervention design groups—8-10 people, usually separately for men and women—to discuss survey results, cost implications, and specific prevention strategies in each community. The exact process for convening the groups varied from place to place, with some participants suggested by community leaders, some being key figures like school teachers, and some identified by door to door invitation. In Managua, facilitators were former volunteers from the feasibility study; in Mexico, they were recent university graduates in social sciences. Communities opted for a range of activities to share basic information on the mosquito life cycle and how to interrupt it (emptying, brushing/scrubbing the interior walls of, or covering receptacles hosting mosquito eggs or larvae); community events to raise awareness, like puppet shows and basketball tournaments; clean up campaigns focused on unoccupied and public premises; introduction of fish into water storage containers (Mexico only); and other activities listed in appendix 2

• Through local community leaders in Nicaragua and directly in Mexico, the research team invited volunteers (brigadistas) from participating communities to receive training as organizers and educators. In all intervention communities, brigadistas visited households and schools to show evidence of larval/pupal infestation in water receptacles, to inform households and schools of the mosquito’s life cycle, and to counsel on ways to interrupt the cycle. Brigadistas also added interventions as their community work advanced (see appendix 2). In Nicaragua, brigadistas received no remuneration; in Mexico, they received allowances for travel, lunch, and child care on the days they worked.

Exchanges between countries informed by the Nicaraguan feasibility study sought commonality of function by assuring the same protocol to generate community led interventions rather than uniformity of the specific actions.18 Mid-stream peer evaluation assessed fidelity to the intervention and dynamics of engagement and encouraged interaction among neighborhoods.

The baseline survey included an entomological survey in the dry season, paired saliva samples before and after the dengue epidemic, and one questionnaire related to dengue and one related to social capital/costs. The baseline survey took place between August 2010 and January 2011. The follow-up impact assessment likewise included an entomological survey in the wet and dry season, paired saliva samples before and after the dengue season, and one questionnaire related to dengue and one related to social capital/costs. In Nicaragua, this was from August 2012 to January 2013 and in Mexico from August to November 2012.

Sequence of steps—The baseline surveys and results from the paired saliva samples preceded, and provided stratifying data for, the randomization. Randomization was followed by the intervention, followed by the impact assessment. The baseline and impact assessments were each made up of two surveys to allow for collection of the paired saliva samples. Serological status from saliva samples was based on differences between the first and second sample. This also enabled vector assessments in the wet and dry season; we report only the dry season entomology assessment.

Timelines—Figure 2 summarizes the timings of the study.⇓

Fig 2 Timeline of study of evidence based community mobilization for dengue prevention in Nicaragua and Mexico

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Outcomes

The primary outcomes were cluster specific rates of dengue virus infection in paired saliva samples (before and after the 2012 dengue season) from children aged 3-9; reported cases of dengue (any age) in the past year; and entomological indices of A aegypti breeding sites. For recent dengue virus infection, during household visits the interviewer asked children to spit 0.5-2 mL of saliva into a plastic receptacle. Reference laboratories in Acapulco and Managua divided this sample into aliquots and stored them at −80°C until they could process paired samples side by side in an IgG capture enzyme linked immunosorbent assay (ELISA). Paired saliva samples collected before and after the dengue epidemic in 2010-11 were processed side by side in the laboratory. We shared these baseline results with the parents and used them to stratify clusters for the randomization. In the final impact assessment, another set of paired saliva samples was collected before and after the dengue epidemic in 2012-13 and processed side by side to determine the final outcome. In this trial, we used a 2× cut off for increase in dengue virus specific IgG units in saliva samples collected before and after the dengue season, based on a previous study.19

We analyzed evidence of infection as households with positive serology results, not individual infections. Quality control included procedures for duplicates and repeating discrepancies.20 We limited serological status to young children because, as a large proportion in this age group has never had a dengue virus infection, we could detect new infections using our assay, which can get saturated by high titres before and after secondary infection. Previous serological studies by our co-authors in Managua showed that over 90% of children aged 10-12 have been exposed to one or more dengue virus serotypes.21 In older age groups, still more people have immunity to one or more serotypes, and it is harder to detect incident secondary infections with our assay. The assay relied on non-invasive saliva samples to estimate incidence of infection in large numbers of participants (low refusal rate). We used self reported dengue as an outcome indicator because, notwithstanding its imperfect reliability, this does include all age groups. The funds and scope of the trial did not permit active surveillance to capture all cases of dengue confirmed by laboratory.

Dengue illness—Self reported cases of dengue were recorded from responses to a direct question about each household member in turn “Did this person suffer from dengue in the last year?”

Vector assessment—Entomology evaluators inspected indoor and outdoor containers, tires, flower vases, water barrels, wash basins, tarpaulins, and discarded containers. The impact assessment focused on household breeding sites; interventions also dealt with breeding sites in open lots and public spaces. Fieldworkers who were not part of the intervention used nets to collect all larvae and pupae from each container. Supervisors transported samples in labeled plastic bags to the respective entomology laboratories for identification. Entomological indices included A aegypti house index (households with larvae or pupae/households examined), container index (containers with larvae or pupae/containers examined), Breteau index (containers with larvae or pupae/households examined), and pupae per person (pupae found/number of residents). There was onebaseline collection in the dry season, and a final assessment in the wet and the dry season. We report here the final assessment in the dry season.

Per protocol secondary outcomes focused on information from face-to-face interviews regarding conscious knowledge about dengue and its prevention and control; attitudes (respondents who agreed to a direct question that temephos and fumigation are the best way to avoid mosquitoes/households interviewed); subjective norms (what neighbors do) and positive deviations from a negative norm; intention to change behavior in the future and to implement preventive action; agency (collective and individual self efficacy)—respondents who said communities can themselves control dengue/households interviewed; discussion—talk with neighbors about how to avoid mosquitoes or prevent dengue; action (interventions, practices)—households that purchased pesticides in the past month; and health literacy, resilience and social capital (see table 3). A separate study, now in progress, will report on the economic costs and implications for sustainability.

Randomization

Sequence generation—Each cluster was a census enumeration area. Computer generated random numbers allocated interventions in each stratum; strata comprised all eligible clusters in each country divided into region and, from the baseline survey, categories of risk of dengue virus infection in children aged 3-9 and vector indices.

Allocation concealment—Intervention status was disclosed once interventions began in both countries.

Implementation—A sampling statistician not engaged in the study conducted random selection from the population census and central random allocation of clusters to intervention.

Masking—Intervention efforts were obvious to residents in intervention sites, and some outcomes (like collective self efficacy) could be influenced by this knowledge. The main outcomes (serological evidence of recent risk of infection and entomological indices) are less susceptible to this bias. As far as possible, interviewers and entomological assessors in the follow-up survey were unaware of intervention status. Data operators were unaware of intervention status.

Estimates of sample size

The 2004-08 Managua feasibility study facilitated estimation of required sample size. Control communities showed serological evidence of recent dengue virus infection in children: 1.5% to 7.4% across 20 non-intervention clusters (intraclass correlation=0.18, estimated by dividing variance between clusters by total variance in the control group). Serology of 40 children in each of 150 clusters (75 clusters per arm) would detect a 33.3% reduction in risk of infection (4.5% to 3%) with 80% power at a significance level of 5%. These calculations assumed equal cluster size, homogeneous treatment effect, and a two sided test with cluster as unit of primary analysis in unmatched parallel groups. Calculations used the approach of Taylor and Bosch for parallel group cluster trials.22

Statistical methods

Data entry and security—Data operators ignorant of intervention status entered household responses twice, with verification of discordant entries from the original questionnaires. A data manager checked digitized data for logical errors.

Principal analysis—We used a t test in an intention to treat analysis of cluster specific rates.23 We included in the analyses the two Nicaraguan intervention sites that declined to participate. Continuous variables in each site were proportions of children showing a more than twofold increase in IgG units between two samples from the same child before and after the dengue season, households with a reported dengue case, and thresholds of conventional entomological indices (above 0). We also used cluster as the unit analysis for our secondary outcomes—household responses to an administered questionnaire. We estimated relative risk reduction (RRR) as 1−relative risk, using variance of the relative risk (Delta method) to estimate confidence intervals. We estimated the number needed to treat (NNT) as the inverse of risk difference (RD) and intraclass correlation (ICC) by dividing the variance between clusters by the variance between and within clusters across the control series.24

Secondary analysis—Per protocol bivariate and then multivariate analysis evaluated impact (evidence of recent dengue virus infection in the household) of living in intervention sites in the context of other factors that might influence infection, mostly household responses to an administered questionnaire. These included temephos exposure (sachets found in water storage containers), household pesticide purchase, household water supply (“How often does your household receive water?”), baseline level of dengue virus infection, and sex of the respondent. We included all those significant at the 5% level (adjusted for cluster) in a generalized linear mixed model (GLMM) with country and cluster as random effects. We report the odds ratio and adjusted odds ratio. Planned subgroup analysis focused on geographic variations of the protective effect, especially population density (urban/rural) and the particular choices of intervention.

Missing data—The follow-up survey included new arrivals in both groups but did not follow those leaving. People who decline to respond might be less involved with dengue control, thus reducing the measured effect. We used Amelia II25 to impute values for missing data with an expectation-maximization algorithm for the primary outcome household report of dengue illness. Estimates reconciled data from 10 imputed datasets with Rubin’s approach26 in the R package Zelig27.

Software—CIETmap28 is open source software with a Windows-like interface for the open source statistical programing language R.