# Infectious Diseases Associated with Exposure to Pollutants in a Local Population from Mexico
## 2 Materials and Methods
### Sample Size  
Informed consent was obtained from all subjects involved in the study for the application of interviews and handling of personal data.  
The study participants consisted of residents of the municipality of Acatzingo, Puebla, Mexico. To determine the sample size, a simple random sampling design was used, considering a two-sided alpha (d) of 0.05, a normal distribution (Z) of 1.96, and a coefficient of variability (CV) of 0.8. The sample size (n) was calculated using the formula recommended by [PERSON] et al. [19] in Equation (1):  
\[\text{n}=(\text{NZ}^{2}\times\text{CV}^{2})/(((\text{N}-1)\text{d}^{2})+(Z^{2} \times\text{CV}^{2})) \tag{1}\]  
where  
N = Represents the total number of producers;  
Z = Normal distribution;  
CV = Coefficient of variability;  
d = Bilateral alpha;  
n = Sample size.  
A semi-structured questionnaire focusing on exposure to contaminants and sociodemographic characteristics was administered to 425 individuals. This data collection aimed to obtain general information and assess the probability of developing infectious diseases associated with exposure to hydrocarbons and pesticides in four geographic zones located in two areas: Acatzingo de Hidalgo and Progreso de Juarez. This sample size was deemed sufficient to detect sample effect sizes of approximately two-thirds of the standard deviation.  
The selection of study zones and participant recruitment was primarily based on the conditions of exposure to hydrocarbons due to the presence of pipelines traversing agricultural areas and households and exposure to pesticides in the vicinity of agricultural plots and field activities.  
In the locality of Acatzingo de Hidalgo (A), different colonies were selected, constituting three geographical areas: Zone 1 (exposure to pesticides) included El Trebol, Tetela, Maravillas, San Antonio, and El Calvario; Zone 2 (exposure to hydrocarbons and pesticides) comprised San Jeronimo Tamariz, El Capulin, Los Corralitos, La Nueva Concepcion, Tres Horas, and San Gabriel; and Zone 3 (exposure to hydrocarbons) included Nuevo Guadalupe. The locality of Progreso de Juarez (B) was designated as Zone 4 (exposure to pesticides) (Figure 1).  
Figure 1: Location of study sites in the municipality of Acatzingo, Puebla, Mexico. Zone 1: Trebol, Tetela, Maravillas, San Antonio, and El Calvario (exposure to pesticides); Zone 2: San Jerónimo, El Capulin, Corralitos, La Nueva Concepción, Tres Horas, and San Gabriel (exposure to hydrocarbons and pesticides); Zone 3: Nuevo Guadalupe (exposure to hydrocarbons); Zone 4: Progreso de Juáñez (exposure to pesticides).  
Respondents were randomly selected at each selected site. Each zone was selected with a homogeneous population size of around 80 to 91 per site; however, in Zone 1, the population size increased due to the very low incidence of infectious diseases.  
Two selection criteria were used; the variables used for grouping were zones (Zone 1, Zone 2, Zone 3, and Zone 4), sex (women and men), occupation (farmer, businessman, housewife, retiree, student, and minors), infectious diseases (once a month or none); and the variables used for stratification were chronic degenerative diseases (type II diabetes mellitus, high blood pressure, breast cancer, leukemia, or none), alcohol consumer (2 times a week, once a week, or no alcohol), smoker (more than 6 cigarettes/week, 1-5 cigarettes/week, or no smoking), and age.