Biomedical subjects

Nicholas P Jewell

Publications and source records attributed to Nicholas P Jewell.

5 recordsLinked to original sources

PubMed2004

Risk behaviors for pesticide exposure among pregnant women living in farmworker households in Salinas, California.

BACKGROUND: Farmworkers and their families are at risk for pesticide exposure, however, little is known about behaviors that increase their risk. We determined the frequency of risky behaviors among pregnant farmworkers and characterized those at greatest risk. METHODS: Participants included 153 pregnant farmworkers and 248 pregnant non-farmworkers who resided with farmworkers from the CHAMACOS (Center for the Health Assessment of Mothers and Children of Salinas) study. We examined risky behaviors relating to handwashing, bathing, protective clothing, house cleaning, laundering of work clothes, wearing of work clothes and shoes into the home, and eating produce from the fields. RESULTS: Between 25 and 60% of women demonstrated risky behavior on each item. Practices of households with pregnant farmworkers and non-farmworkers did not differ. Women who lived in the United States longer, and in crowded households demonstrated the most risky behavior overall. CONCLUSIONS: Pregnant farmworkers and those living with farmworkers need to be educated to reduce potential take-home pesticide exposure.

Adolescent↗

PubMed2004

Maximum likelihood estimation of ordered multinomial parameters.

The pool adjacent violator algorithm Ayer et al. (1955, The Annals of Mathematical Statistics, 26, 641-647) has long been known to give the maximum likelihood estimator of a series of ordered binomial parameters, based on an independent observation from each distribution (see Barlow et al., 1972, Statistical Inference under Order Restrictions, Wiley, New York). This result has immediate application to estimation of a survival distribution based on current survival status at a set of monitoring times. This paper considers an extended problem of maximum likelihood estimation of a series of 'ordered' multinomial parameters p(i)= (p(1i),p(2i),.,p(mi)) for 1 <or=i <ro=k, where ordered means that p(j1) <or=p(j2) <or=<or=p(jk) for each j with 1 <or=j <or=m-1. The data consist of k independent observations X(1),., X(k) where X(i) has a multinomial distribution with probability parameter p(i) and known index n(i)\geq 1. By making use of variants of the pool adjacent violator algorithm, we obtain a simple algorithm to compute the maximum likelihood estimator of p(1),., p(k), and demonstrate its convergence. The results are applied to nonparametric maximum likelihood estimation of the sub-distribution functions associated with a survival time random variable with competing risks when only current status data are available (Jewell et al. 2003, Biometrika, 90, 183-197).

Age Factors↗

PubMed2004

Formulation and evaluation of a predictive model to identify the sites of future diabetic retinopathy.

PURPOSE: To formulate and test a model to predict the development of local patches of nonproliferative diabetic retinopathy (NPDR), based on multifocal electroretinogram (mfERG) implicit times and candidate diabetic risk factors. METHODS: mfERGs and fundus photographs were obtained from 28 eyes of 28 diabetic patients during an initial and 12-month follow-up examination. mfERG implicit times were derived at 103 locations using a template-stretching method, and a z-score was calculated in comparison with 20 age-matched normal subjects. Thirty-five nonoverlapping retinal zones were constructed by grouping two to three adjacent stimulated locations, and each zone was assigned the maximum z-score within it. Zones containing initial retinopathy were excluded from further analysis. The probability that new retinopathy would develop in the remaining zones by the follow-up examination was modeled based on the mfERG implicit time z-score for the zone and other candidate diabetic risk factors determined during the initial visit. Data collected from four previously untested diabetic subjects and the other eye of eight previous subjects during their second year follow-up were used to test the predictive model. RESULTS: After 1 year, new retinopathy developed in 11 of the 12 NPDR eyes and 1 of the 16 eyes without initial retinopathy. After accounting for the correlation among zones within each eye, a predictive model was formulated with the variables mfERG implicit time, duration of diabetes, presence of retinopathy (NPDR or no retinopathy), and blood glucose level at initial visit. The area under the receiver operating characteristic (ROC) curve of this multivariate model is 0.90 (P <0.001). The predictive model has an expected sensitivity of 86% and a specificity of 84%, which was verified by the test data. CONCLUSIONS: The development of diabetic retinopathy over a 1-year period can be well predicted by a multivariate model. The inclusion of local mfERG implicit times allowed the model to identify the specific sites of future retinopathy.

Adult↗

PubMed2004

Association of in utero organophosphate pesticide exposure and fetal growth and length of gestation in an agricultural population.

Although pesticide use is widespread, little is known about potential adverse health effects of in utero exposure. We investigated the effects of organophosphate pesticide exposure during pregnancy on fetal growth and gestational duration in a cohort of low-income, Latina women living in an agricultural community in the Salinas Valley, California. We measured nonspecific metabolites of organophosphate pesticides (dimethyl and diethyl phosphates) and metabolites specific to malathion (malathion dicarboxylic acid), chlorpyrifos [O,O-diethyl O-(3,5,6-trichloro-2-pyridinyl) phosphoro-thioate], and parathion (4-nitrophenol) in maternal urine collected twice during pregnancy. We also measured levels of cholinesterase in whole blood and butyryl cholinesterase in plasma in maternal and umbilical cord blood. We failed to demonstrate an adverse relationship between fetal growth and any measure of in utero organophosphate pesticide exposure. In fact, we found increases in body length and head circumference associated with some exposure measures. However, we did find decreases in gestational duration associated with two measures of in utero pesticide exposure: urinary dimethyl phosphate metabolites [beta(adjusted) = -0.41 weeks per log10 unit increase; 95% confidence interval (CI), -0.75 -- -0.02; p = 0.02], which reflect exposure to dimethyl organophosphate compounds such as malathion, and umbilical cord cholinesterase (beta(adjusted) = 0.34 weeks per unit increase; 95% CI, 0.13-0.55; p = 0.001). Shortened gestational duration was most clearly related to increasing exposure levels in the latter part of pregnancy. These associations with gestational age may be biologically plausible given that organophosphate pesticides depress cholinesterase and acetylcholine stimulates contraction of the uterus. However, despite these observed associations, the rate of preterm delivery in this population (6.4%) was lower than in a U.S. reference population.

Adolescent↗

PubMed2003

Severe acute respiratory syndrome: temporal stability and geographic variation in case-fatality rates and doubling times.

We analyzed temporal stability and geographic trends in cumulative case-fatality rates and average doubling times of severe acute respiratory syndrome (SARS). In part, we account for correlations between case-fatality rates and doubling times through differences in control measures. Factors that may alter future estimates of case-fatality rates, reasons for heterogeneity in doubling times among countries, and implications for the control of SARS are discussed.

China↗