Is the water safe for my baby?

Children's behavior and physiology place them at unique risk from waterborne microbial and chemical contaminants. This article reveals children's susceptibility factors and the microbial and chemical contaminants of greatest importance to this age group. It also provides a primer on water treatment and alternatives to tap water. This article concludes with recommendations and resources to aid the practicing pediatrician in addressing patient concerns about drinking water.

Variations in concepts of "susceptibility" in risk assessment.

The Food Quality Protection Act and the 1996 amendments to the Safe Drinking Water Act are two of the most recent examples of legislation calling for protection of susceptible subpopulations. As regulatory deadlines draw nearer, controversies in scientific and policy arenas increase about incorporating susceptibility in risk assessment. The previously accepted working definition of "susceptibility" has already been called into question. Part of the controversy results from different disciplines conceiving of susceptibility in different ways. Understanding the conceptual differences embodied within definitions can provide a basis on which a revised working definition may be developed across disciplines. The purposes of this article are to describe the varying definitions of susceptibility, discuss the differing concepts incorporated in the definitions, and recommend ways in which susceptibility may be defined and framed to meet current risk assessment needs. The present analysis of definitions from the fields of ecology, biology, engineering, medicine, epidemiology, and toxicology revealed different emphases that relate to the underlying perspectives and methods of each field. It is likely that susceptibility will need to be formally defined for public policy purposes, but until that time, the use of more informal communication and decision-making processes is suggested to develop and utilize a new working consensus on the definition of susceptibility.

Can varying concepts of susceptibility in risk assessment affect particulate matter standards?

The Clean Air Act mandates that sensitive subpopulations be considered in setting standards to protect the public's health. The purposes of this paper are to point out different conceptualizations of susceptibility, examine how it is approached in risk-related processes, and recommend ways it may be more explicitly framed for risk assessment and management purposes. We studied the traditional risk assessment paradigm, the U.S. Environmental Protection Agency (EPA) guidelines and revised PM standard, discussions from recent interdisciplinary meetings, and peer-reviewed literature. Areas of controversy include what factors intrinsic and extrinsic to the host should be incorporated in susceptibility, what health endpoints are of concern, whether susceptibility is deterministic or stochastic, and whether it should be defined on an individual or population scale. Recent discussions about susceptibility applied to PM indicate that it needs to be more clearly defined and evaluated for scientific and policy purposes. We conclude that varying concepts of susceptibility can affect risk-related processes such as PM standard setting. We recommend that susceptibility be clearly defined in the problem statement of risk assessments and be addressed in a specific subsection of risk characterization, integrating all susceptibility findings from the prior three steps in the risk assessment paradigm.

Simple visual reaction time in organolead manufacturing workers: influence of the interstimulus interval.

The authors conducted this investigation to study the effects of interstimulus interval duration for a given simple visual reaction time trial on the relationship between lead exposure and reaction time. Organolead manufacturing workers (n=222) and nonexposed referents (n=62) were administered a neurobehavioral test battery that included simple visual reaction time. Simple visual reaction time was measured over 44 trials; interstimulus intervals ranged from 1 to 10 s in a randomly generated sequence that was identical for all study subjects. Mean reaction times for both lead-exposed and nonexposed subjects were longest for interstimulus intervals of 1 and 2 s. Mean reaction times in response to moderate (4-6 s) and long (7-10 s) interstimulus intervals were mainly associated with lead exposure; this association led the authors to suggest that interstimulus interval duration modifies the relationship between lead exposure and simple visual reaction time performance. In simple visual reaction time protocols, stronger associations between reaction time and lead exposure may be found if the analysis trials are separated with interstimulus intervals of less than 3 s duration.

Simple visual reaction time in organolead manufacturing workers: comparison of different methods of modeling lead exposure and reaction time.

In March 1990, 222 organolead manufacturing workers and 62 nonexposed referents were administered a neurobehavioral test battery that included simple visual reaction time (SVRT). SVRT was measured over 44 trials with interstimulus intervals ranging from 1 to 10 sec in a random but fixed order for all study subjects. Different measures of lead exposure and dose (e.g., recent and cumulative exposure based on personal sampling data, exposed/nonexposed status, recent blood lead and zinc protoporphyrin levels, and peak and cumulative urine lead levels) were examined as predictors of several different parameters of SVRT (e.g., mean, median, truncated mean, and standard deviation of SVRT over 44 trials). The association varied, depending on the measures used for SVRT and lead exposure and dose. In linear regression analyses, the strongest and most consistent associations of lead exposure and dose were observed with the standard deviation of SVRT. In assessing the different exposure measures, strong and consistent associations were observed with blood lead levels at the time of SVRT testing, but not with recent or cumulative exposure measures. That is, stronger associations were observed with measures of relatively recent internal dose (i.e., blood lead level) than with cumulative measures (i.e., cumulative exposure). Future studies using SVRT should consider parameters of SVRT that have not been commonly used to date, such as the standard deviation of the SVRT.

Global climate change and emerging infectious diseases.

Climatic factors influence the emergence and reemergence of infectious diseases, in addition to multiple human, biological, and ecological determinants. Climatologists have identified upward trends in global temperatures and now estimate an unprecedented rise of 2.0 degrees C by the year 2100. Of major concern is that these changes can affect the introduction and dissemination of many serious infectious diseases. The incidence of mosquito-borne diseases, including malaria, dengue, and viral encephalitides, are among those diseases most sensitive to climate. Climate change would directly affect disease transmission by shifting the vector's geographic range and increasing reproductive and biting rates and by shortening the pathogen incubation period. Climate-related increases in sea surface temperature and sea level can lead to higher incidence of water-borne infectious and toxin-related illnesses, such as cholera and shellfish poisoning. Human migration and damage to health infrastructures from the projected increase in climate variability could indirectly contribute to disease transmission. Human susceptibility to infections might be further compounded by malnutrition due to climate stress on agriculture and potential alterations in the human immune system caused by increased flux of ultraviolet radiation. Analyzing the role of climate in the emergence of human infectious diseases will require interdisciplinary cooperation among physicians, climatologists, biologists, and social scientists. Increased disease surveillance, integrated modeling, and use of geographically based data systems will afford more anticipatory measures by the medical community. Understanding the linkages between climatological and ecological change as determinants of disease emergence and redistribution will ultimately help optimize preventive strategies.