Agua SALud:
Epidemiological Study
Introduction
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.
Exposed |
Unexposed |
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.(www.ssa.gob.mx
accessed on 19th May, 2004)
[iii] Normas Oficiales
Mexicana. NOM-030-SSA2 1999. Para la prevención, tratamiento y control de la
hipertensión arterial sistémica (www.salud.gob.mx/unidades/cdi/nom/030ssa29.html,
accessed on May 26th, 2004).