Summary of Mexico Baseline Results

Young brigadistas visiting a household to give a mother the results of her children’s saliva samples, taken during the baseline measurement in Costa Grande.

For the baseline study in Guerrero, we visited 12,399 households, with a total of 54,728 residents, in 90 clusters in the Acapulco, Costa Grande and Costa Chica regions. The visits were conducted in December 2009 and between May and June 2010. Fifty-four percent of the households were in rural areas and 46% in urban areas.

We spoke with one informant per household, mostly women. We gathered 12,764 saliva samples from 6,382 children between 3 to 9 years of age (one sample in each of the two visits); overall, we analysed 25,528 samples, since each pair of samples was submitted to a duplicate analysis. We also monitored 45 thousand water containers.

Incidence of dengue infection

Overall, two percent of the survey population were reported to have suffered from dengue in the previous year. Incidence rates were higher among children and youth between 5 and 24 years of age; among these groups, 20% of those surveyed had been ill with dengue fever.

Acapulco was the most affected area, with a 3.5% reported incidence of infection. Dengue risk was almost six times higher in Acapulco than in Costa Chica, the least affected area. In Costa Grande, dengue risk was 2.5 times higher than in Costa Chica. Dengue risk was twice as high in urban areas compared to rural areas. However, the vector is already present in all rural sites, which could make this health problem even worse.

Recent dengue virus infection

Six percent of children aged between three and nine years had been bitten by a mosquito carrying the dengue virus in the months between the two saliva samples. This incidence was higher in the Acapulco region (9%) than in Costa Grande (5%) and Costa Chica (4%). Higher risk factors included being male, being three to four years of age, living in urban areas, living in Acapulco, belonging to households where mosquito prevention was not discussed with neighbours and not carrying out control activities at home.

Presence of breeding sites, larvae and pupae

In all three study areas we inspected 45 thousand containers. We found Aedes aegypti larvas in 16% of surveyed households. Entomological indexes were higher in the Costa Chica area than in Acapulco and Costa Grande, despite the fact that dengue virus infection and disease rates were lower in Costa Chica.

The main Aedes mosquito breeding sites found in households are standard water storage containers, such as tanks, barrels and buckets; this is perhaps due to the lack of a regular water supply. Among small containers, we found larvas more often in tires, plant and flower pots, cans, glasses, toys, unused bathrooms and flasks.

Costs of the disease

The economic burden of dengue on a family is high. On average, a family had spent 1,076 pesos (17 days’ work for those earning the minimum wage) per case of dengue. Among those who received treatment in public health facilities, the average expenditure was 643 pesos; in private facilities the expense was almost three times higher: 1,923 pesos. Affected households lost, on average, 12 work days due to illness from dengue or the need to look after a household member with the illness. Of those who had been ill, 20% were hospitalised in a public or private institution; these patients spent an average of 2,207 pesos.

Knowledge, attitudes and intentions

Most households considered their risk of becoming ill from dengue low (45%) or nil (30%). Only 24% stated that they were at high risk. It was more likely for risk to be perceived in households where someone had suffered from dengue in the previous year. Almost all interview participants were able to physically identify the larvas, but only 20% linked them to the dengue vector mosquito.

In terms of attitudes, nearly all interview participants said it would be worth eliminating mosquito breeding sites from the household. Some 83% believed their neighbours thought the same way. As for the intention to do or not do something in the short- or medium-term, almost everyone said they planned to eliminate breeding sites in their homes. 75% felt that dengue control depends on them, 11% thought it depends on healthcare staff and 12% that it depends on both groups. The vast majority (90%) said they talk little or not at all with their neighbours about how to eliminate the mosquito in their neighbourhood. Only 20% had met with their neighbours to talk about the subject.

Actions for prevention and control

Half of the households had not undertaken any activities to control the mosquito; 40% had cleaned and 7% had eliminated pots and other containers. Among those who undertook activities, almost all said it had yielded results. Some of these actions were also carried out in community spaces.

We found temephos in only half the households, even though using this larvicide is one of the main components of the government’s program to fight dengue. Some 18% of the earthenware jars we inspected contained temephos, even though the Official Mexican Norm states that they must not be treated with larvicides, since they tend to contain drinking water. Half of those interviewed thought that temephos can have negative effects for those who drink water containing it.

Forty-four percent of households burned spiral or sprayed aerosol pesticides. The probability of someone having been sick from dengue was higher among these households. It is possible that using these products increases risk due to the feeling of protection it gives users.