Agua SALud: Epidemiological Study



The World Health Organization (WHO) estimates that 1/6 (1.1 billion people) of the world’s population was without access to an improved water supply in 2000.  The impact of the lack of access to water on people’s health is illustrated by the fact that the WHO has ranked the combined effects of water, sanitation, and hygiene as the 3rd leading preventable cause of disability and death in high mortality developing countries, after unsafe sex and malnutrition.  Recent estimates indicate that water, sanitation, and hygiene directly account for 2.2 million deaths each year, more than 90% of these are children under age five.


Mexico’s state of Baja California Sur (population: 489,669) consists of an arid and abrupt landscape speckled with many small rural communities with just a few cities.  Although the cities and major towns have access to fresh water, a considerable number of the smaller remote communities only have access to brackish-water wells. When possible, inhabitants of these communities travel long distances by foot or boat, to obtain the fresh water needed for their families. It is often the case that people do not have an alternative to drinking water from their brackish wells despite salinity levels well beyond those recommended by the Mexican Government and the US EPA.


With regard to sodium intake, there is a clear relationship between habitual consumption and high blood pressure levels. Population based studies have shown that lowering sodium intake is associated with a reduction of systolic blood pressure. However, the health effects associated with the consumption of high saline water remains elusive.


There were two specific aims of the epidemiological study based on the absence of information available on the impact that consuming water of high salinity and otherwise poor quality has on blood pressure and on acute diarrheal episodes in rural communities of Baja California Sur. The first was to document the impact of water salinity on blood pressure and the second was to estimate the disease frequency of diarrhea in children under five in rural villages. Our main exposure was intake of high-saline water and the main dependent variable was hypertension. Diarrhea prevalence in children under five was assessed by using health and sanitation related questionnaires on mothers in the communities visited.



Materials and Methods

According to the National Health Survey (EMSA-2000) conducted in the year 2000 and directed to determine the prevalence of non-communicable chronic diseases in Mexico, the prevalence of hypertension in subjects aged between 20-69 years old was 30.05%[i].  Sample size was estimated using EPI INFO version 6. Calculations were based on an odds ratio of 2, an 80% power, an alpha of 0.05% and a 1:1 ratio of unexposed to exposed. According to our estimates, 306 participants 20 to 69 years old were required. Inclusion criteria for the study were the subject’s age (20 to 69 years) and residence (living in the community for at least one year).


Due to logistical reasons, we chose to survey communities affiliated with the rural schools program of the National Council for the Promotion of Education (CONAFE). Information with regard to total population of the community, qualitative assessment of water saltiness, and water source of the community was collected in the preliminary survey which was sent on May, 2004 and answered one month later by the assigned CONAFE instructor in each community.


Preliminary surveys were sent to 128 villages, of these, 113 responded. The data of 9 villages were not considered due to incomplete information. In order to conduct questionnaires on the entire eligible population of each community and thus decrease selection bias, villages of 110 or less inhabitants were chosen. On the other hand, due to time and money constraints, villages of over 40 inhabitants were selected. The former led to 62 eligible villages. Communities were divided in two groups based on exposure: (“salty” taste in water destined for human consumption and “no salty” taste). According to B.C.S.’s statistics 57% of the population is 20 to 69 years old. Based on an 80% participation rate, we estimated that 14 to 18 villages would be necessary to complete the sample size. Random sampling of each group (exposed and unexposed) was performed using MatLab 6.5. The final list of randomly selected communities is presented in the following table.




1. Boca del Sauzoso

1. Boca del Álamo

2. Santa Fe

2. La Ceiba

3. El Médano

3. La Palmilla

4. Fortuna del Bajío

4. Palma Sola

5. Punta Coyote

5. Punta Alta

6. Las Animas

6. Ensenada de Cortes

7. San Nicolás

7. Puerto Dátil

8. El Sacrificio

8. El Peloteado

9. Cadejé

9. Laguneros


10. Santa Cruz


11. San Miguel

List of villages selected randomly. Exposure was based on qualitative assessment of water “saltiness”.


The number of villages to be visited was determined by the total number of inhabitants per community, the former information was extracted from the statistics given by INEGI and crossed referenced when possible with the responses from the preliminary surveys. However, during the data collection phase the number of participants was less than expected therefore, two communities were added: El Rosario and Conquista Agraria. 


Based on the 2002 statistics provided by the National Ministry of Health for the state of Baja California Sur, the prevalence of acute diarrheal disease in children under five was 23.8%[ii]. The frequency of diarrhea disease was assessed in the visited communities. Given that children under 5 represent 10% of the state’s population, based on an 80% participation rate we estimated that 56 to 72 questionnaires would be conducted.


Two types of questionnaires were designed. The first questionnaire was targeted at adults between 20-69 years old and aimed at assessing the association between consumption of high saline water and hypertension. At the end of the survey, blood pressure, height and weight of participants were measured. The case definition of hypertension was based on  previous medical diagnosis of the disease with intake of anti-hypertensive medication, or if the average of 2 blood pressure recordings taken at least 2 minutes apart[iii] resulted in a systolic BP equal to or greater 160mmHg or a diastolic BP equal to or greater than 90 mmHg.


The second type of questionnaire was targeted at mothers or legal guardians of children under five. It aimed at identifying the prevalence and risk factors associated with diarrhea in the child. Weight and height of the infant were assessed at the end. The case definition of diarrhea was defined as three or more loose stools in 24hr. The recall period was the preceding week, as recommended by the World Health Organization.


[i] Peralta Rosas. Arterial Hypertension in Mexico and its association with other risk factors. Arch Cardiol Mex, 2003; 73 Suppl 1: S137-40

[ii] Dirección General de Epidemiología/SSA. Veinte primeras causas de enfermedad en BCS. Distribución de casos por grupo de edad, 2002.( accessed on 19th May, 2004)

[iii] Normas Oficiales Mexicana. NOM-030-SSA2 1999. Para la prevención, tratamiento y control de la hipertensión arterial sistémica (, accessed on May 26th, 2004).