Glenn O. Ware

Comparison of six dose-response models for use with food-borne pathogens.

Food-related illness in the United States is estimated to affect over six million people per year and cost the economy several billion dollars. These illnesses and costs could be reduced if minimum infectious doses were established and used as the basis of regulations and monitoring. However, standard methodologies for dose-response assessment are not yet formulated for microbial risk assessment. The objective of this study was to compare dose-response models for food-borne pathogens and determine which models were most appropriate for a range of pathogens. The statistical models proposed in the literature and chosen for comparison purposes were log-normal, long-logistic, exponential, beta-Poisson and Weibull-Gamma. These were fit to four data sets also taken from published literature, Shigella flexneri, Shigella dysenteriae, Campylobacter jejuni, and Salmonella typhosa, using the method of maximum likelihood. The Weibull-gamma, the only model with three parameters, was also the only model capable of fitting all the data sets examined using the maximum likelihood estimation for comparisons. Infectious doses were also calculated using each model. Within any given data set, the infectious dose estimated to affect one percent of the population ranged from one order of magnitude to as much as nine orders of magnitude, illustrating the differences in extrapolation of the dose response models. More data are needed to compare models and examine extrapolation from high to low doses for food-borne pathogens.

Nonhuman Primate Model for Listeria monocytogenes-Induced Stillbirths

ABSTRACT Listeria monocytogenes, isolated from outbreaks in either human or nonhuman primate populations, was administered orally at doses ranging from 106 to 1010 CFU. Four of 10 treated animals delivered stillborn infants. L. monocytogenes was isolated from fetal tissue, and the pathology was consistent with L. monocytogenes infection as the cause of pregnancy loss. For all pregnancies resulting in stillbirths, L. monocytogenes was isolated from maternal feces, indicating that L. monocytogenes had survived and had probably colonized the gastrointestinal tract. Antibodies and antigen-specific lymphocyte proliferation against Listeria increased in animals that had stillbirths.

Dose-Response Model for Listeria monocytogenes-Induced Stillbirths in Nonhuman Primates

ABSTRACT A dose-response model using rhesus monkeys as a surrogate for pregnant women indicates that oral exposure to 107 CFU of Listeria monocytogenes results in about 50% stillbirths. Ten of 33 pregnant rhesus monkeys exposed orally to a single dose of 102 to 1010 CFU of L. monocytogenes had stillbirths. A log-logistic model predicts a dose affecting 50% of animals at 107 CFU, comparable to an estimated 106 CFU based on an outbreak among pregnant women but much less than the extrapolated estimate (1013 CFU) from the FDA-U.S. Department of Agriculture-CDC risk assessment using an exponential curve based on mouse data. Exposure and etiology of the disease are the same in humans and primates but not in mice. This information will aid in risk assessment, assist policy makers, and provide a model for mechanistic studies of L. monocytogenes-induced stillbirths.

Effect of exposure to low level lead on growth and growth hormone release in rats

This study was undertaken to examine the effect of exposure to low level lead on growth and growth hormone (GH) release. Female pups exposed to lead beginning in utero were smaller than controls on postnatal day 7 (P = 0.06). There was no corresponding effect in males. No overall differences in body weights were detected in either sex with respect to treatment effect. No differences in food or water intake were observed at any time. Pituitaries from 49-day-old lead-treated pups responded to in vitro incubation with growth hormone releasing factor (GRF) with a smaller increase in GH release than those from control pups (P = 0.08). In the case of the dams, lead did not affect body weight, body length, food consumption or pituitary responsiveness; however, water consumption was significantly increased in the lactating dam (P < 0.05). Interestingly, blood lead content in 5-day-old pups (43.3 +/- 2.7 micrograms/dl) exposed to lead in utero was more than twice that of their 49-day-old litter-mates (18.9 +/- 0.7 micrograms/dl). At 49 days blood lead levels in female pups (19.94 +/- 0.8 micrograms/dl) were significantly higher than those of male pups (17.00 +/- 1.1 micrograms/dl). Maternal blood lead levels on the same day averaged 22.7 +/- 2.5 micrograms/dl. This study suggests that exposure to a low level of lead can reduce pituitary responsiveness to a hypothalamic stimulus. In addition, the data reinforce the importance of considering age and sex when evaluating the toxic effects of lead.

Factors influencing production of inflorescence-derived somatic seedlings of sweetgum

Somatic embryos derived from staminate inflorescence tissues of three mature sweetgum (Liquidambar styraciflua) trees were tested for germination and conversion frequencies and early growth variables following pregermination cold treatments. Individual mature embryos were selected from repetitively embryogenic cultures maintained on Woody Plant Medium (WPM) with 1 mg l−1 naphthaleneacetic acid and cultured on basal WPM at 10 8C for 0, 4 or 8 weeks prior to being transferred to WPM germination medium in the light. After 4 weeks, germinated embryos were planted in potting mix in an acclimatization chamber, grown for an additional 8 weeks and evaluated for conversion and growth. Conversion frequency, which ranged up to 80%, was affected by ortet and clonal line, while the number of first-order lateral roots was affected by ortet, clonal line and cold treatment, with 8 weeks of cold promoting the highest number.

A General Statistical Model for Estimating Future Demand Levels of Data-Base Utilization within an Information Retrieval Organization.

A statistical model for characterizing the growth patterns of data base utilization and for estimating future utilization levels of demand has been developed for information retrieval organizations. The model developed is γ = β (1‐e−at) where γ is the number of users of a data base at time †, and α and β are parameters to be estimated. Illustrations of the model applied to a typical information retrieval organization are given and discussed.

Estimating shrinkage of container media mixtures with linear and/or regression models

Abstract Shrinkage occurs when container medium components of different particle sizes are mixed which poses a major problem in computer modeling of container media. We have devised a theoretical model, linear in nature, which requires shrinkage determination only at the 1: 1 v/v proportions and that predicts shrinkage in binary and ternary mixes. Therefore, it is simple, rapid and economical to use. Regression models were also utilized to characterize shrinkage estimation, but they require a large number of laboratory determinations to develop and are cumbersome to use in comparison to the theoretical model.

A management planning model for the delivery of family planning services.

Abstract A management planning model for the delivery of family planning services is presented. Markovian probabilistic properties have been adapted for projecting patient flow for a set of various alternative strategies for scheduling patient visits in a health care system. By quantitatively formulating the scheduling problem in terms of pertinent inputs, management objectives and imposed restrictions, optimization of patient flow in the system for efficient utilization of health care resources is achieved through standard linear programming techniques.

A general statistical model for characterizing the growth patterns and projecting the level of performance of family planning clinics

Abstract A statistical model for characterizing the growth patterns and projecting the level of performance has been developed for family planning clinics. The model developed is y = β (1 − e−αt where y is the number of continuing contraceptive patients at time t, and α and β are parameters to be estimated. Results of a typical application of the model are presented and discussed.