Pupal productivity in rainy and dry seasons: findings from the impact survey of a randomised controlled trial of dengue prevention in Guerrero, Mexico.

BACKGROUND: The follow-up survey of a cluster-randomised controlled trial of evidence-based community mobilisation for dengue control in Nicaragua and Mexico included entomological information from the 2012 rainy and dry seasons. We used data from the Mexican arm of the trial to assess the impact of the community action on pupal production of the dengue vector Aedes aegypti in both rainy and dry seasons. METHODS: Trained field workers inspected household water containers in 90 clusters and collected any pupae or larvae present for entomological examination. We calculated indices of pupae per person and pupae per household, and traditional entomological indices of container index, household index and Breteau index, and compared these between rainy and dry seasons and between intervention and control clusters, using a cluster t-test to test significance of differences. RESULTS: In 11,933 houses in the rainy season, we inspected 40,323 containers and found 7070 Aedes aegypti pupae. In the dry season, we inspected 43,461 containers and counted 6552 pupae. All pupae and entomological indices were lower in the intervention clusters (IC) than in control clusters (CC) in both the rainy season (RS) and the dry season (DS): pupae per container 0.12 IC and 0.24 CC in RS, and 0.10 IC and 0.20 CC in DS; pupae per household 0.46 IC and 0.82 CC in RS, and 0.41 IC and 0.83 CC in DS; pupae per person 0.11 IC and 0.19 CC in RS, and 0.10 IC and 0.20 CC in DS; household index 16% IC and 21% CC in RS, and 12.1% IC and 17.9% CC in DS; container index 7.5% IC and 11.5% CC in RS, and 4.6% IC and 7.1% CC in DS; Breteau index 27% IC and 36% CC in RS, and 19% IC and 29% CC in DS. All differences between the intervention and control clusters were statistically significant, taking into account clustering. CONCLUSIONS: The trial intervention led to significant decreases in pupal and conventional entomological indices in both rainy and dry seasons. TRIAL REGISTRATION: ISRCTN27581154 .

"Where we put little fish in the water there are no mosquitoes:" a cross-sectional study on biological control of the Aedes aegypti vector in 90 coastal-region communities of Guerrero, Mexico.

BACKGROUND: In the Mexican state of Guerrero, some households place fish in water storage containers to prevent the development of mosquito larvae. Studies have shown that larvivorous fish reduce larva count in household water containers, but there is a lack of evidence about whether the use of fish is associated with a reduction in dengue virus infection. We used data from the follow up survey of the Camino Verde cluster randomised controlled trial of community mobilisation to reduce dengue risk to study this association. METHODS: The survey in 2012, among 90 clusters in the three coastal regions of Guerrero State, included a questionnaire to 10,864 households about socio-demographic factors and self-reported cases of dengue illness in the previous year. Paired saliva samples provided serological evidence of recent dengue infection among 4856 children aged 3-9 years. An entomological survey in the same households looked for larvae and pupae of Aedes aegypti and recorded presence of fish and temephos in water containers. We examined associations with the two outcomes of recent dengue infection and reported dengue illness in bivariate analysis and then multivariate analysis using generalized linear mixed modelling. RESULTS: Some 17% (1730/10,111) of households had fish in their water containers. The presence of fish was associated with lower levels of recent dengue virus infection in children aged 3-9 years (OR 0.64; 95% CI 0.45-0.91), as was living in a rural area (OR 0.57; 95% CI 0.45-0.71), and being aged 3-5 years (OR 0.65; 95% CI 0.51-0.83). Factors associated with lower likelihood of self-reported dengue illness were: the presence of fish (OR 0.79; 95% CI 0.64-0.97), and living in a rural area (OR 0.74; 95% CI 0.65-0.84). Factors associated with higher likelihood of self-reported dengue illness were: higher education level of the household head (OR 1.28; 95% CI 1.07-1.52), living in a household with five people or less (OR 1.33; 95% CI 1.16-1.52) and household use of insecticide anti-mosquito products (OR 1.68; 95% CI 1.47-1.92). CONCLUSIONS: Our study suggests that fish in water containers may reduce the risk of dengue virus infection and dengue illness. This could be a useful part of interventions to control the Aedes aegypti vector.

Aedes aegypti breeding ecology in Guerrero: cross-sectional study of mosquito breeding sites from the baseline for the Camino Verde trial in Mexico.

BACKGROUND: Understanding the breeding patterns of Aedes aegypti in households and the factors associated with infestation are important for implementing vector control. The baseline survey of a cluster randomised controlled trial of community mobilisation for dengue prevention in Mexico and Nicaragua collected information about the containers that are the main breeding sites, identified possible actions to reduce breeding, and examined factors associated with household infestation. This paper describes findings from the Mexican arm of the baseline survey. METHODS: In 2010 field teams conducted household surveys and entomological inspections in 11,995 households from 90 representative communities in the three coastal regions of Guerrero State, Mexico. We characterized Ae. aegypti breeding sites and examined the effect of two preventive measures: temephos application in water containers, and keeping the containers covered. We examined associations with household infestation, using bivariate and multivariate analysis adjusted for clustering effects. RESULTS: We conducted entomological inspections in 11,995 households. Among 45,353 water containers examined, 6.5% (2958/45,353) were positive for larvae and/or pupae. Concrete tanks (pilas) and barrels (tambos) together accounted for 74% of pupal productivity. Both covering water containers and inserting temephos were independently associated with a lower risk of presence of larvae or pupae, with the effect of covering (OR 0.22; 95% CIca 0.15-0.27) stronger than that of temephos (OR 0.66; 95% CIca 0.53-0.84). Having more than four water containers was associated with household infestation in both rural areas (OR 1.42; 95% CIca 1.17-1.72) and urban areas (1.81; 1.47-2.25), as was low education of the household head (rural: 1.27; 1.11-1.46, and urban: 1.39; 1.17-1.66). Additional factors in rural areas were: household head without paid work (1.31; 1.08-1.59); being in the Acapulco region (1.91; 1.06-3.44); and using anti-mosquito products (1.27; 1.09-1.47). In urban areas only, presence of temephos was associated with a lower risk of household infestation (0.44; 0.32-0.60). CONCLUSION: Concrete tanks and barrels accounted for the majority of pupal productivity. Covering water containers could be an effective means of Ae. aegypti vector control, with a bigger effect than using temephos. These findings were useful in planning and implementing the Camino Verde trial intervention in Mexico.

Occurrence of scorpion sting and associated factors in a highly marginalized municipality in Guerrero, Mexico: A cross-sectional study.

BACKGROUND: Scorpion sting is a neglected public health problem, despite a global estimate of 1.2 million scorpion stings and some 3,250 deaths annually. METHODS: This cross-sectional study estimates the occurrence of scorpion stings and identifies associated factors in seven communities in the highly marginalized municipality of Chilapa, in the Mexican state of Guerrero. After informed consent, 1,144 households provided information on 4,985 residents. The questionnaire collated sociodemographic data, characteristics of the dwelling, efforts to avoid scorpion stings, and individual information of scorpion stings suffered in the last year. Cluster-adjusted (acl), bivariate and multivariate analysis relied on the Mantel-Haenszel procedure. RESULTS: The overall period prevalence of scorpion stings in the year prior to the study was 4.4% (218/4985), 5.4% in men (126/2320), and 3.5% in women (92/2665), p<0.01. The majority occurred at home 68.3% (149/218), followed by agricultural fields 26.6% (58/218), street 2.8% (6/218), and work 2.3% (5/218). Factors associated with scorpion sting were carrying firewood (OR 2.1; CI95%acl 1.40-3.09), keeping free-range hens around of the home (OR 1.9; CI95%acl 1.19-2.85), residing in a rural area (OR 1.7; CI95%acl 1.04-2.78), being male (OR 1.6; CI95%acl 1.18-2.28), and helping with housework (OR 1.6; CI95%acl 1.04-2.40). CONCLUSION: This study confirms scorpion bites are a public health problem in these marginalized communities in Guerrero State, with risk factors related to living conditions and the work process at home and in the fields. Almost all risk factors identified could be reduced with low-cost interventions implemented by the communities themselves.

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

OBJECTIVE: To test whether community mobilization adds effectiveness to conventional dengue control. DESIGN: Pragmatic open label parallel group cluster randomized controlled trial. Those assessing the outcomes and analyzing the data were blinded to group assignment. Centralized computerized randomization after the baseline study allocated half the sites to intervention, stratified by country, evidence of recent dengue virus infection in children aged 3-9, and vector indices. SETTING: Random sample of communities in Managua, capital of Nicaragua, and three coastal regions in Guerrero State in the south of Mexico. PARTICIPANTS: Residents in a random sample of census enumeration areas across both countries: 75 intervention and 75 control clusters (about 140 households each) were randomized and analyzed (60 clusters in Nicaragua and 90 in Mexico), including 85,182 residents in 18,838 households. INTERVENTIONS: A community mobilization protocol began with community discussion of baseline results. Each intervention cluster adapted the basic intervention-chemical-free prevention of mosquito reproduction-to its own circumstances. All clusters continued the government run dengue control program. MAIN OUTCOME MEASURES: Primary outcomes per protocol were self reported cases of dengue, serological evidence of recent dengue virus infection, and conventional entomological indices (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). Per protocol secondary analysis examined the effect of Camino Verde in the context of temephos use. RESULTS: With cluster as the unit of analysis, serological evidence from intervention sites showed a lower risk of infection with dengue virus in children (relative risk reduction 29.5%, 95% confidence interval 3.8% to 55.3%), fewer reports of dengue illness (24.7%, 1.8% to 51.2%), fewer houses with larvae or pupae among houses visited (house index) (44.1%, 13.6% to 74.7%), fewer containers with larvae or pupae among containers examined (container index) (36.7%, 24.5% to 44.8%), fewer containers with larvae or pupae among houses visited (Breteau index) (35.1%, 16.7% to 55.5%), and fewer pupae per person (51.7%, 36.2% to 76.1%). The numbers needed to treat were 30 (95% confidence interval 20 to 59) for a lower risk of infection in children, 71 (48 to 143) for fewer reports of dengue illness, 17 (14 to 20) for the house index, 37 (35 to 67) for the container index, 10 (6 to 29) for the Breteau index, and 12 (7 to 31) for fewer pupae per person. Secondary per protocol analysis showed no serological evidence of a protective effect of temephos. CONCLUSIONS: Evidence based community mobilization can add effectiveness to dengue vector control. Each site implementing the intervention in its own way has the advantage of local customization and strong community engagement. TRIAL REGISTRATION: ISRCTN27581154.