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In order to identify risk factors associated with human exposure to fluoride in San Luis Potosi (SLP), Mexico, a biochemical and epidemiological study was carried out in 1992. Results from the analysis of fluoride sources showed that 61% of tap water samples had fluoride levels above the optimal level of 0.7-1.2 ppm. The levels were higher after boiling. In bottled water, fluoride levels ranged from 0.33 to 6.97 ppm. These sources are important since in SLP 82% of the children drink tap water, 31% also drink bottled water, 92% prepare their food with tap water, 44% boiled all the drinking water, and 91% used infant formula reconstituted with boiled water. The prevalence and severity of dental fluorosis in children (11-13 years old) increased as the concentration of water fluoride increased. At levels of fluoride in water lower than 0.7 ppm a prevalence of 69% was found for total dental fluorosis, whereas at levels of fluoride in water higher than 2.0 ppm a prevalence of 98% was found. In the same children, fluoride levels in urine were quantified. The levels increased as the concentration of water fluoride increased. Regressional analysis showed an increment of 0.54 ppm (P < 0.0001) of fluoride in urine for each ppm of fluoride in water. Fluoride urinary levels were higher in samples collected during the afternoon (1800) when compared with sample collected during the morning (1100). Taking together all these results, three risk factors for human exposure to fluoride in SLP can be identified: ambient temperature, boiled water, and food preparation with boiled water. These factors explain the prevalence of dental fluorosis in SLP.

To summarize the evidence of acute health effects from exposure to particulate matter and ozone.A meta-analysis was performed using random effect models, to summarize the health effects of pollution, published in major international and Mexican journals up to June 2000.Results were given as percent increase in ten units of PM10 (microgram/m3) and ozone (ppb). PM10 was found to have an effect on mortality (0.96%), hospital admissions (1.39%), emergency room visits (3.11%), respiratory symptoms (7.72%), pulmonary forced vital capacity (1.42%), and restricted activity days (7.74%). Ozone effects were equally significant.These findings show the great impact that air pollutants may have on the health of populations living in large metropolis.

To identify factors (particularly social, economic and cultural), associated with the risk of death from pulmonary tuberculosis in Mexico.A case-control study of patients receiving medical attention from the official health services of Veracruz, Mexico. Cases were deaths from pulmonary tuberculosis in 1993. Controls were survivors randomly selected from the State Tuberculosis Case Registry. Next of kin provided information for both cases and controls.Multivariate analysis of 161 cases and 161 controls showed an increased risk of dying for those patients who withdrew from treatment (odds ratio [OR] = 3.52), who were refused medical attention during some period of time in any health center (OR = 4.45), and who had a concomitant disease at the time of diagnosis (OR = 2.62). A linear trend with age was observed (OR = 1.02 per year), as well as a lower risk for those patients who were compliant with treatment and optimistic about surviving the disease (OR = 0.17). The risk of death was not associated with the presence of a health care unit in the town, time spent to get to the health center, or the residence of a patient in an urban area.These findings indicate that deaths due to tuberculosis in this area are not related to the geographical distribution of health services but to delays in treatment after the onset of disease and to the low adherence of patients to the treatment regimen.

The aim of this paper is to present a conceptual and practical framework of the case-control design in medical research. To illustrate this method, practical examples directed to clinicians and other health professionals interested in medical research are presented. The case-control method is very versatile and allows for multiple applications. Guidelines for the selection of cases and controls, and some considerations on sample size are presented. In the statistical analysis we use concrete examples of how to estimate odds ratios, confidence intervals, and methods to control for potential confounders, from stratified analysis to logistic regression.

Daily death counts in Mexico City were examined in relation to ambient ozone levels during 1990-1992 for the purpose of investigating the acute, irreversible effects of air pollution, with emphasis on ozone exposure. Air pollution data were obtained from nine monitoring stations operated by the Departamento del Distrito Federal. Mortality data were provided by the Instituto Nacional de Estadística, Geografía, e Informática. Increases in numbers of deaths were positively associated with elevated air pollution levels on the same day and on the previous day. The magnitude of the increases was small but statistically significant, after Poisson regression models were used to adjust for temperature and long-term trends. In models using data for a single pollutant, the "crude" ratio for total mortality associated with an increase of 100 parts per billion (ppb)* in one-hour maximum ozone concentration was 1.029 (95% CI 1.015, 1.044). A moving average of ozone showed a stronger association (rate ratio [RR] = 1.048, 95% CI 1.025, 1.070), and excess mortality (an increase in the number of deaths, relative to the average on days with low pollution levels) was more evident for persons over 65 years of age. Separate analyses of the effect of elevated ozone for different areas of the city showed similar results, but they were not statistically significant. Other pollutants also were related to mortality. The RR was 1.075 (95% CI 0.984, 1.062) per 100-ppb increase for sulfur dioxide and 1.049 (95% CI 1.030, 1.067) per 100 micrograms/m3 increase in total suspended particulates (TSP) when these pollutants were considered in separate models. However, when all three pollutants were considered simultaneously, only TSP remained associated with mortality, indicating excess mortality of 5% per 100 micrograms/m3 increase [RR = 1.052, 95% CI 1.034, 1.072]. The excess mortality associated with TSP is consistent with that observed in other cities in America and Europe. This study provides some evidence that ozone is associated with all-cause mortality and with mortality among the elderly after controlling for long-term cycles. However, ozone levels exhibited little or no effect on mortality rates when other air pollutants were considered simultaneously. Particulate matter appeared to be an important pollutant; it independently predicted changes in mortality. Nevertheless, because of the complexity and variability of the mixtures to which people are exposed, it is difficult to attribute the observed effects to a single pollutant. The technical feasibility and scientific validity of isolating the effect of single pollutants in such complex mixtures requires further research and careful consideration. Given the large population living in and exposed to ambient air pollution in Mexico City and other metropolises throughout the world, these small but significant associations of mortality with air pollution indices are of public health concern.

We describe the socio-demographic and medical care characteristics of people who died of pulmonary tuberculosis in 1993 in the state of Veracruz, Mexico.Once selected, through death certificate, an interview and verbal autopsy was applied to the closest available relative.A total of 300 interviews were carried out. Half of the deaths were diagnosed with tuberculosis the same year they died. Approximately half of the deceased withdrew from treatment and 40% reported abuse of alcohol consumption. Patients who died of pulmonary tuberculosis belonged to the most vulnerable social groups. 35% were illiterate or had no education, and 67% lacked a regular job. There were no differences found between those who used private medical services and those who used official or public services.Important findings include the high proportion of patients diagnosed in advanced stages of the disease, alcoholism, adverse reactions to drugs as a cause of withdrawal from treatment, and other current diseases at the time of tuberculosis diagnosis.

In order to identify risk factors associated with human exposure to fluoride in San Luis Potosi (SLP), Mexico, a biochemical and epidemiological study was carried out in 1992. Results from the analysis of fluoride sources showed that 61% of tap water samples had fluoride levels above the optimal level of 0.7-1.2 ppm. The levels were higher after boiling. In bottled water, fluoride levels ranged from 0.33 to 6.97 ppm. These sources are important since in SLP 82% of the children drink tap water, 31% also drink bottled water, 92% prepare their food with tap water, 44% boiled all the drinking water, and 91% used infant formula reconstituted with boiled water. The prevalence and severity of dental fluorosis in children (11-13 years old) increased as the concentration of water fluoride increased. At levels of fluoride in water lower than 0.7 ppm a prevalence of 69% was found for total dental fluorosis, whereas at levels of fluoride in water higher than 2.0 ppm a prevalence of 98% was found. In the same children, fluoride levels in urine were quantified. The levels increased as the concentration of water fluoride increased. Regressional analysis showed an increment of 0.54 ppm (P0.0001) of fluoride in urine for each ppm of fluoride in water. Fluoride urinary levels were higher in samples collected during the afternoon (1800) when compared with sample collected during the morning (1100). Taking together all these results, three risk factors for human exposure to fluoride in SLP can be identified: ambient temperature, boiled water, and food preparation with boiled water. These factors explain the prevalence of dental fluorosis in SLP.

In the search for methods to support the decision making process and to maximize the benefit resulting from the health priorities, this paper discusses the investment-production-consumption model (IPC). This method attempts to quantify the socio-economic impact of mortality. This type of evaluation takes into account age at death and the potential for future productivity and thus assesses the generation of losses or gains to society, depending on the stage of life in which death occurs. The impact of different causes of death estimated by this method is illustrated from the cause of Mexico. These results are compared with the relative importance attributed by the use of mortality rates and years of potential life lost. The ordering by rates shows heart diseases, accidents and tumors as first causes of deaths. On the other hand, the indicator of years of potential life lost shows causes of death at younger ages to occupy the first place. The YPLLipc, however, gives greater importance to infections, accidents and homicides.

Studies of the effect of depression on life expectancy have found controversial results. In the past, an excess mortality was attributed to conditions seen at psychiatric institutions. More recently, in addition to an excess mortality due to violent causes of death, some studies also found excess mortality due to non-violent and all-cause mortality. Hospital studies that evaluated this relationship are generally flawed and lack of control for potential confounders. Underlying physical illnesses could explain the excess mortality reported. On the other hand, community-based studies have studied small number of depressed subjects, and have used diverse measurements of depression which hamper comparability. This paper critically reviews recent published studies and discusses possible mechanisms for this association.

With the purpose of describing the role of malnutrition at death time, an analysis of multiple causes of death in children under five years-old was performed on deaths which occurred during April and May 1985 in Mexico City. A proportional mortality analysis was done taking in consideration all the causes listed on the death certificate, not only the underlying causes. The number of deaths associated to malnutrition was greater by multiple cause than by underlying cause (OR = 7.9, 95% CI 5.0-12.7, p = 0.00000). The importance of considering multiple causes of death, mainly when there are frequent diseases which are some times recorded as underlying cause of death, is also discussed.

In order to validate mortality studies, we described the role of hypertension at the time of death of people who died during April and May 1985. This analysis take into account all the causes listed in death certificates and not only the underlying cause. A proportional mortality design was used to evaluate the relationship of hypertension, cerebrovascular and cardiovascular disease. The number of deaths associated to hypertension was larger by multiple cause than by underlying cause. The odds ratio for hypertension and ischemic heart disease was 4.1 adjusted by age and sex, and 21.1 for cerebrovascular disease.

The main aim was to assess the role of anticoagulant therapy (AT) in reducing the mortality for patients with acute myocardial infarction (AMI). A pair-matched case-control study was designed according to three confounding factors: gender, age (+/- 5 years), and hospitalization date (+/- 13 months). Cases were defined as patients with AMI who died during hospitalization and controls were those patients with AMI who survived. Excluded from the study were patients with strong indications or contraindications for use of AT, and also those with early death (less than 12 hr). The study undertaken at the National Institute of Cardiology "Ignacio Chávez" of Mexico City and all necessary information was obtained from clinical charts of patients discharged between the period from January 1, 1975 to December 31, 1985. Complete information was accomplished for 212 pairs of cases and controls. A protective odds ratio (favoring use of AT) = 12.1 (p less than 0.0001, 95% CI 4.2-34.9) was obtained by means of a multiple logistic regression analysis by conditional method. Other variables that entered into the logistic model were: antithrombotic therapy, severity measured by Killip scale and by Norris index. Such findings support the favorable therapeutic role of AT in patients with AMI.

The carcinogenic effects of ionizing radiation at high doses are un questionable. On the other hand, the deleterious exposure effects to low doses have not been totally proven, mainly due to methodological problems and difficulty in measuring reliable dose exposure. In this paper, some recent studies examining the effects of ionizing radiation in some occupational groups are reviewed and discussed. Also, the main areas of epidemiologic controversy are stressed. For future experiences, prospective, longitudinal studies with occupational cohorts, measuring radiation exposure with adequate registry and follow-up, are suggested.

Due to changes in mortality patterns, cronic and degenerative diseases have become a major problem in Mexico. Description and explanation of this kind of deaths is difficult by means of a single cause of death. In order to have a better understanding of this fenomenum an analysis of 4021 deaths occurred in Mexico city during april and may in 1985 using multiple cause of death was performed, this analysis take count of all causes reported in death certificates. With the method of multiple cause we found that the number of associated deaths, for example with hypertension and nutritional deficiencies, was considerably greater that when reported as underlying cause.

During health care services planning, rational and coherent information is required in order to allocate resources in accordance with local relative need. In an attempt to recognize the national condition, Stone's method was used. This is a semi-quantitative method for analysing the relationship between health care resources and need. Years of potential life lost index was used for need assessment among the states, and confronted to its Federal Public Health Investment. The optimum resource/need ratio is regarded as that pertaining to the reference population, the nation as a whole. Deviation from the optimum ratio in the states is interpreted as a manifestation of inequitable resource distribution. The results show striking differences in needs and resources. Resource/need ratio varied from 0.21 in Oaxaca to 3.79 in Distrito Federal. The states least favoured in resource sharing were Oaxaca, Puebla, Hidalgo and México. On the other hand, Tamaulipas, Baja California Sur, Quintana Roo and Distrito Federal exceeded the optimum. These indexes permit a quantitative expression of the relationship between need and resources in order to reach geographical equity.