THE NATURAL BACKGROUND GAMMA RADIATION EXPOSURE IN THE METROPOLITAN AREA OF THE VALLEY OF MEXICO

Measurements of the natural background radiation have been made at numerous places throughout the world. Very little work in this field has been done in developing countries. In Mexico the natural radiation to which the population is exposed has not been assessed. This dissertation represents a pioneer study in this environmental area. The radiation exposure which occupants within buildings receive as a result of naturally occurring radionuclides present in construction materials is the principal focus.^ Data were collected between August 1979 and November 1980. Continuous monitoring was done with TLDs placed on site for periods of 3 to 6 months. The instrumentation used for "real-time" measurements was a portable NaI (Tl) scintillation detector. In addition, radiometric measurements were performed on construction materials commonly used in Mexican homes.^ Based on TLD readings taken within 75 dwellings, the typical indoor exposure for a resident of the study area is 9.2 (mu)Rh('-1). The average reading of the 152 indoor scintillometer surveys was 9.5 (mu)Rh('-1), the outdoor reading 7.5 (mu)Rh('-1). Results of one-way and multi-way analyses of the exposure data to determine the effect due to building materials type, geologic subsoil, age of dwelling, and elevation are also presented. The results of 152 indoor scintillometer surveys are described. ^

West Nile virus in the Rio Grande Valley: A seroprevalence study of juvenile dogs

This study used canine sentinel surveillance and collected a sample of adult mosquitoes to investigate the potential impact of West Nile virus (WNV) in human populations in the Rio Grande Valley along the Texas-Mexico border. Samples for this study were collected from juvenile dogs two months to one year of age in animal shelters located in the Rio Grande Valley. The sample was comprised of stray dogs in order to include animals with maximum nighttime exposures to Culex mosquitoes. Serum samples were collected following the 2007 WNV transmission season and were tested for IgG antibodies against WNV. Evidence of antibodies to WNV was found in 35.1% of the sample population consisting of 74 dogs. During this same time period, mosquitoes in Brownsville were trapped and morphologically identified to develop greater understanding of the mosquito populations in the region and to further understand other potential mosquito vectors for disease transmission. The vast majority of mosquitoes living in this area were Aedes albopictus (47.6%), Culex quinquefasciatus (23.7%), and Aedes aegypti (20.1%). This study shows that WNV and the vector responsible for WNV transmission are active in the Rio Grande Valley and pose a threat to the human and animal populations. ^

Occupational performance of Mexican Americans with end-stage-renal-disease living on dialysis in the lower Rio Grande Valley

The number of people with end-stage-renal-disease (ESRD) and living with dialysis is a growing public health concern. Most studies about the impact of ESRD on people’s lives have placed attention on the medical and clinical dimension of ESRD. Very few have given attention to the environmental and cultural context in which people with ESRD live, the adaptation that these individuals must make to adjust to living with ESRD and dialysis, or the occupations in which they engage. Additionally these studies have not focused on Mexican Americans who are disproportionately affected by this illness and condition. This qualitative study explores the needs, perceptions, and issues facing Mexican Americans with ESRD living with dialysis as well as their families. Participants were residents of the Lower Rio Grande Valley and included individuals with ESRD, family members, and the healthcare providers who give care to them. The Health Belief Model and Lifestyle Performance Model served as the theoretical frameworks. The study also explored the daily occupations of this population. ^ In-depth interviews were conducted on 15 Mexican Americans with ESRD living with dialysis, 15 family members, and six dialysis healthcare providers. A video documentary of the day-to-day life of three individuals with ESRD and their families was produced. Such data do not currently exist and will greatly enhance the understanding of the human experience of living with ESRD. The results suggest that a collective effort of the family unit is at work to deal with the demands of dialysis. An imbalance and disharmony exist among the occupational activities, which creates occupational deprivation and disruption for both the individuals and family members. Implications for practice and recommendations for further research are described. ^

Statistical and methodological challenges for disaster preparedness and medical needs assessment in Rio Grande Valley of Texas

In recent years, disaster preparedness through assessment of medical and special needs persons (MSNP) has taken a center place in public eye in effect of frequent natural disasters such as hurricanes, storm surge or tsunami due to climate change and increased human activity on our planet. Statistical methods complex survey design and analysis have equally gained significance as a consequence. However, there exist many challenges still, to infer such assessments over the target population for policy level advocacy and implementation. ^ Objective. This study discusses the use of some of the statistical methods for disaster preparedness and medical needs assessment to facilitate local and state governments for its policy level decision making and logistic support to avoid any loss of life and property in future calamities. ^ Methods. In order to obtain precise and unbiased estimates for Medical Special Needs Persons (MSNP) and disaster preparedness for evacuation in Rio Grande Valley (RGV) of Texas, a stratified and cluster-randomized multi-stage sampling design was implemented. US School of Public Health, Brownsville surveyed 3088 households in three counties namely Cameron, Hidalgo, and Willacy. Multiple statistical methods were implemented and estimates were obtained taking into count probability of selection and clustering effects. Statistical methods for data analysis discussed were Multivariate Linear Regression (MLR), Survey Linear Regression (Svy-Reg), Generalized Estimation Equation (GEE) and Multilevel Mixed Models (MLM) all with and without sampling weights. ^ Results. Estimated population for RGV was 1,146,796. There were 51.5% female, 90% Hispanic, 73% married, 56% unemployed and 37% with their personal transport. 40% people attained education up to elementary school, another 42% reaching high school and only 18% went to college. Median household income is less than $15,000/year. MSNP estimated to be 44,196 (3.98%) [95% CI: 39,029; 51,123]. All statistical models are in concordance with MSNP estimates ranging from 44,000 to 48,000. MSNP estimates for statistical methods are: MLR (47,707; 95% CI: 42,462; 52,999), MLR with weights (45,882; 95% CI: 39,792; 51,972), Bootstrap Regression (47,730; 95% CI: 41,629; 53,785), GEE (47,649; 95% CI: 41,629; 53,670), GEE with weights (45,076; 95% CI: 39,029; 51,123), Svy-Reg (44,196; 95% CI: 40,004; 48,390) and MLM (46,513; 95% CI: 39,869; 53,157). ^ Conclusion. RGV is a flood zone, most susceptible to hurricanes and other natural disasters. People in the region are mostly Hispanic, under-educated with least income levels in the U.S. In case of any disaster people in large are incapacitated with only 37% have their personal transport to take care of MSNP. Local and state government’s intervention in terms of planning, preparation and support for evacuation is necessary in any such disaster to avoid loss of precious human life. ^ Key words: Complex Surveys, statistical methods, multilevel models, cluster randomized, sampling weights, raking, survey regression, generalized estimation equations (GEE), random effects, Intracluster correlation coefficient (ICC).^

Confidential inquiry into perinatal mortality in the Lower Rio Grande Valley, 1988

A review of 1985 neonatal death statistics in the Lower Rio Grande Valley of Texas revealed an excessive perinatal death rate among Hispanics compared to Anglos. In order to identify factors contributing to perinatal mortality in the region and to determine if existing perinatal services were adequate, a confidential inquiry into each 1988 perinatal death was performed.^ Medical risk factors in the mothers were infrequent. The most commonly noted pregnancy complication was polyhydramnios. This complication is often associated with anencephalus which was the most frequent birth anomaly detected in the region.^ The study results did not reveal an association between lay midwife deliveries in the region and excessive perinatal mortality nor did perinatal mortality appear to be associated with a lack of neonatal intensive care facilities. Lack of prenatal care was the most commonly encountered preventable factor associated with perinatal death. It was not possible to determine if the level of care for Anglos and Hispanics differed because of the low number of Anglo deaths although the socioeconomic level of deaths in each of the ethnic groups was the same. ^

Seroprevalence of Chagas' disease in Texas among shelter dogs in Houston and the Rio Grande Valley region and its implication for human infection

Chagas’ disease, also called American Trypanosomiasis, is a vector-borne disease caused by the protozoan parasite Trypanosoma cruzi. T. cruzi is spread by triatomine insects, commonly referred to as ‘kissing bugs.’ After the insect takes a blood meal from its animal or human host, it usually defecates near the bite wound. The parasite is present in the feces, and when rubbed into the bite wound or mucous membranes by the host, infection ensues. Chagas’ disease is highly endemic in Central and South America where it originated. Many people in these endemic areas live in poor conditions surrounded by animals, mainly dogs, that can serve as a possible link to human infection. In Chagas’ endemic countries, dogs can be used as a sentinel to infer risk for human infection. In Texas, the prevalence of Chagas’ and risk for human infection is largely unknown. This study aimed to determine the prevalence of Chagas’ disease in shelter dogs in Houston, Texas and the Rio Grande Valley region by using an immunochromatographic assay (Chagas’ Stat-Pak) to test for the presence of T. cruzi antibodies. Of the 822 samples tested, 26 were found to be positive (3.2%). In both locations, Chagas’ prevalence increased over time. This study found that dogs, especially strays, can serve as sentinels for disease activity. Public health authorities can implement this strategy to understand the level of Chagas’ activity in a defined geographic area and prevent human infection.^