Absorption of wireless radiation in the child versus adult brain and eye from cell phone conversation or virtual reality.

Children's brains are more susceptible to hazardous exposures, and are thought to absorb higher doses of radiation from cell phones in some regions of the brain. Globally the numbers and applications of wireless devices are increasing rapidly, but since 1997 safety testing has relied on a large, homogenous, adult male head phantom to simulate exposures; the "Standard Anthropomorphic Mannequin" (SAM) is used to estimate only whether tissue temperature will be increased by more than 1 Celsius degree in the periphery. The present work employs anatomically based modeling currently used to set standards for surgical and medical devices, that incorporates heterogeneous characteristics of age and anatomy. Modeling of a cell phone held to the ear, or of virtual reality devices in front of the eyes, reveals that young eyes and brains absorb substantially higher local radiation doses than adults'. Age-specific simulations indicate the need to apply refined methods for regulatory compliance testing; and for public education regarding manufacturers' advice to keep phones off the body, and prudent use to limit exposures, particularly to protect the young.

Recent diarrhea is associated with elevated salivary IgG responses to Cryptosporidium in residents of an eastern Massachusetts community.

BACKGROUND: Serological data suggest that Cryptosporidium infections are common but underreported. The invasiveness of blood sampling limits the application of serology in epidemiological surveillance. We pilot-tested a non-invasive salivary anti-Cryptosporidium antibody assay in a community survey involving children and adults. MATERIALS AND METHODS: Families with children were recruited in a Massachusetts community in July; symptoms data were collected at 3 monthly follow-up mail surveys. One saliva sample per person (n = 349) was collected via mail, with the last survey in October. Samples were analyzed for IgG and IgA responses to a recombinant C. hominis gp15 sporozoite protein using a time-resolved fluorometric immunoassay. Log-transformed assay results were regressed on age using penalized B-splines to account for the strong age-dependence of antibody reactions. Positive responses were defined as fluorescence values above the upper 99% prediction limit. RESULTS: Forty-seven (13.5%) individuals had diarrhea without concurrent respiratory symptoms during the 3-month-long follow-up; eight of them had these symptoms during the month prior to saliva sampling. Two individuals had positive IgG responses: an adult who had diarrhea during the prior month and a child who had episodes of diarrhea during each survey month (Fisher's exact test for an association between diarrhea and IgG response: p = 0.0005 for symptoms during the prior month and p = 0.02 for symptoms during the entire follow-up period). The child also had a positive IgA response, along with two asymptomatic individuals (an association between diarrhea and IgA was not significant). CONCLUSION: These results suggest that the salivary IgG specific to Cryptosporidium antigens warrants further evaluation as a potential indicator of recent infections.

Quantum adiabatic optimization and combinatorial landscapes.

In this paper we analyze the performance of the Quantum Adiabatic Evolution algorithm on a variant of the satisfiability problem for an ensemble of random graphs parametrized by the ratio of clauses to variables, gamma=M/N . We introduce a set of macroscopic parameters (landscapes) and put forward an ansatz of universality for random bit flips. We then formulate the problem of finding the smallest eigenvalue and the excitation gap as a statistical mechanics problem. We use the so-called annealing approximation with a refinement that a finite set of macroscopic variables (instead of only energy) is used, and are able to show the existence of a dynamic threshold gamma= gamma(d) starting with some value of K -the number of variables in each clause. Beyond the dynamic threshold, the algorithm should take an exponentially long time to find a solution. We compare the results for extended and simplified sets of landscapes and provide numerical evidence in support of our universality ansatz. We have been able to map the ensemble of random graphs onto another ensemble with fluctuations significantly reduced. This enabled us to obtain tight upper bounds on the satisfiability transition and to recompute the dynamical transition using the extended set of landscapes.

Sexual selection, redundancy and survival of the most beautiful.

A model is described of a highly redundant complex organism that has overlapping banks of genes such that each vital function is specified by several different genetic systems. This generates a synergistic profile linking probability of survival to the number of deleterious mutations in the genome. Computer models show that there is a dynamic interaction between the mean number of new deleterious mutations per generation (X), the mean number of deleterious mutations in the genome of the population (Y) and percentage zygote survival (Zs). Increased X leads to increased Y and a fall in Zs but it takes several generations before a new equilibrium is reached. If sexual attraction is influenced by the number of deleterious mutations in the genome of individuals then Y is reduced and Zs increased for any given value of X. This fall in Y and rise in Zs is more marked in polygamous than monogamous mating systems. The model is specified such that deleterious mutations can occur without any observable or measurable effect on function. Thus sexual selection, in this organism, for low levels of deleterious mutations cannot be based on assessment of performance. Instead it is based on a simple symmetrical surface pattern that is flawlessly reproduced by organisms with no deleterious mutations, but is less than perfect, and therefore less attractive, if genetic systems have been deleted. A complex vital task requires a system with a high level of redundancy that acts so that the loss of one component has no observable effect and therefore cannot be used for sexual selection. The reproduction of a beautiful surface pattern also requires a low error, high redundancy genetic system; however, in this case there is advantage if a single deleterious mutation produces a recognisable change. This leads to the conclusion that sexual selection and sexual attraction should be based on beauty rather than utility, and explains the common observation in nature that it is the most beautiful that survive.

The conservation of redundancy in genetic systems: effects of sexual and asexual reproduction.

The relationship between probability of survival and the number of deleterious mutations in the genome is investigated using three different models of highly redundant systems that interact with a threatening environment. Model one is a system that counters a potentially lethal infection; it has multiple identical components that act in sequence and in parallel. Model two has many different overlapping components that provide threefold coverage of a large number of vital functions. The third model is based on statistical decision theory: an ideal detector, following an optimum decision strategy, makes crucial decisions in an uncertain world. The probability of a fatal error is reduced by a redundant sampling system, but the chance of error rises as the system is impaired by deleterious mutations. In all three cases the survival profile shows a synergistic pattern in that the probability of survival falls slowly and then more rapidly. This is different than the multiplicative or independent survival profile that is often used in mathematical models. It is suggested that a synergistic profile is a property of redundant systems. Model one is then used to study the conservation of redundancy during sexual and asexual reproduction. A unicellular haploid organism reproducing asexually retains redundancy when the mutation rate is very low (0.001 per cell division), but tends to lose high levels of redundancy if the mutation rate is increased (0.01 to 0.1 per cell division). If a similar unicellular haploid organism has a sexual phase then redundancy is retained for mutation rates between 0.001 and 0.1 per cell division. The sexual organism outgrows the asexual organism when the above mutation rates apply. If they compete for finite resources the asexual organism will be extinguished. Variants of the sexual organism with increased redundancy will outgrow those with lower levels of redundancy and the sexual process facilitates the evolution of more complex forms. There is a limit to the extent that complexity can be increased by increasing the size of the genome and in asexual organisms this leads to progressive accumulation of mutations with loss of redundancy and eventual extinction. If complexity is increased by using genes in new combinations, the asexual form can reach a stable equilibrium, although it is associated with some loss of redundancy. The sexual form, by comparison, can survive, with retention of redundancy, even if the mutation rate is above one per generation. The conservation and evolution of redundancy, which is essential for complexity, depends on the sexual process of reproduction.

The mathematical basis of sexual attraction.

Computer programs have been written to study the dynamic interaction in humans between environmental mutagenesis, the genomic load of deleterious mutations and the probability of zygote survival. The human genome is complex and highly redundant and as a consequence deleterious mutations accumulate. The computer programs are based on a model of the human genome in which deleterious mutations interact synergistically causing impaired performance in individual systems and this leads to a positive correlation between the total number of deleterious mutations in the genome and impaired performance across the whole spectrum of biological capability. This includes performance in intellectual tasks, sporting ability, the ability to fight disease and preserve health and the development of a symmetrical physical form. Sexual reproduction distributes deleterious mutations unequally amongst zygotes and the model predicts that zygote survival will correlate negatively with zygote mutational load. The computer simulation shows that rising environmental mutagenesis will lead to a rise in the human genomic mutational load and to decreased zygote survival, although the full effect would take several generations. If this occurred the health of future generations would suffer and methods to monitor environmental mutagenesis are required. The model also shows that a marked rise in environmental mutagenesis would lead to species extinction if mate choice were random, i.e., unrelated to the genomic mutational load. The biological imperfections caused by mutations, however, in health, intelligence and physical symmetry are all, to varying degrees, related to sexual attraction. The model shows that if mates are chosen in response to sexual attraction the species can be maintained in the presence of high environmental mutagenesis. A polygamous pattern in which females mate with a minority of males has the most marked effect in reducing the number of deleterious mutations in the next generation. The model also shows that as environmental mutagenesis falls the number of eligible males would increase and a species would change from a polygamous to a monogamous pattern of mating. These results imply that we are not attracted by good genes, but by a lack of bad genes. Sexual attraction is a force which counteracts genomic degradation.

Serum dioxin and cognitive functioning among veterans of Operation Ranch Hand.

We used the Halstead-Reitan neuropsychological test battery, the Wechsler adult intelligence scale-revised, the Wechsler memory scale, and the wide range achievement test to assess cognitive functioning among Air Force veterans exposed to Agent Orange and its contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin), during the Vietnam war The index subjects were veterans of Operation Ranch Hand (N = 937), the unit responsible for aerial herbicide spraying in Vietnam from 1962 to 1971. A comparison group of other Air Force veterans (N= 1,052), who served in Southeast Asia during the same period but were not involved with spraying herbicides served as referents. Cognitive functioning was assessed in 1982, and dioxin levels were measured in 1987 and 1992. We assigned each Ranch Hand veteran to the background, low, or high dioxin exposure category on the basis of a measurement of dioxin body burden. Although we found no global effect of dioxin exposure on cognitive functioning, we did find that several measures of memory functioning were decreased among veterans with the highest dioxin exposure. These results became more distinct when we restricted the analysis to enlisted personnel, the subgroup with the highest dioxin levels. An analysis based on dioxin quintiles in the combined cohort produced consistent results, with veterans in the fifth quintile exhibiting reduced verbal memory function. Although statistically significant, these differences were relatively small and of uncertain clinical significance.

Airborne particulates and hospital admissions for cardiovascular disease: a quantitative review of the evidence.

This is a quantitative review of studies characterizing the relationship between exposure to airborne particulates and hospital admissions for cardiovascular disease. A MEDLINE search and a review of reference lists were conducted to identify time-series studies that considered particles less than 10 microm or 2.5 microm in diameter (PM(10) and PM(2.5), respectively) and their association with day-to-day variation in cardiovascular admissions. The results of these studies were standardized to give estimates of the percentage increase in hospital admissions associated with an increase in ingestion of ambient particles of 10 microg/m3. The results were grouped and compared on the basis of the specific outcomes and exposure measures. When studies that considered the association between PM(10) exposure and specific cardiovascular outcomes were pooled (after exclusion of outliers), a 10-microg/m(3) increase in PM(10) was associated with increases in admission rates of 0.8% (95% confidence interval [CI]: 0.5, 1.2%) for congestive heart failure, 0.7% (95% CI: 0.4, 1.0%) for ischemic heart disease, and 0.2% (95% CI: -0.2, 0.6%) for cerebrovascular accidents. These effects tended to diminish substantially when gaseous co-pollutants were considered. The extent to which these effects are due to fine particles is unclear. The available studies indicate that exposure to airborne particles is associated with hospital admissions for cardiovascular disease; but the magnitude of this effect depends strongly on the specific disease category being considered, the time lag used in the analysis, and the type and amount of co-pollutants. Future studies should include careful consideration of the role of co-pollutants in this association, the interaction of particles with temperature, the impact of particle size on this effect, and the extent to which the observed effect involves short-term "harvesting."

Linking sight and sound: fMRI evidence of primary auditory cortex activation during visual word recognition.

We describe two studies that used repetition priming paradigms to investigate brain activity during the reading of single words. Functional magnetic resonance images were collected during a visual lexical decision task in which nonword stimuli were manipulated with regard to phonological properties and compared to genuine English words. We observed a region in left-hemisphere primary auditory cortex linked to a repetition priming effect. The priming effect activity was observed only for stimuli that sound like known words; moreover, this region was sensitive to strategic task differences. Thus, a brain region involved in the most basic aspects of auditory processing appears to be engaged in reading even when there is no environmental oral or auditory component.

Relation between Kaufman Brief Intelligence Test and WISC-III scores of children with RD.

Concurrent validity of the Kaufman Brief Intelligence Test (K-BIT) with the Wechsler Intelligence Scale for Children-Third Edition (WISC-III) was evaluated, as well as the K-BIT's accuracy as a predictor of WISC-III scores, in a sample of young children with reading disabilities. The two measures were administered to 65 children from Atlanta, Boston, and Toronto who ranged from 6-5 to 7-11 years of age at testing. Correlations between the verbal, nonverbal, and composite scales of the K-BIT and WISC-III were .60, .48, and .63, respectively. Mean K-BIT scores ranged from 1.2 to 5.0 points higher than the corresponding WISC-III scores. Standard errors of estimation ranged from 10.0 to 12.3 points. In individual cases, K-BIT scores can underestimate or overestimate WISC-III scores by as much as 25 points. Results suggest caution against using the K-BIT exclusively for placement and diagnostic purposes with young children with reading disabilities if IQ scores are required.

Social problem solving in children with acquired brain injuries.

OBJECTIVES: To assess the performance of children with acquired brain injuries (ABIs) on a measure of social problem solving and to examine the relationships between participant characteristics and performance on the Social Knowledge Interview (SKI) and between parent-reported child behavior and performance on the SKI. DESIGN: Between-group comparisons using correlational analyses, matched pairs t-tests, and analysis of covariance (ANCOVA). PARTICIPANTS: Thirty-one children 6-12 years old with ABI and 31 control participants, matched on age and sex. MAIN OUTCOME MEASURE: The SKI, a measure of social problem-solving skills. RESULTS: Using matched pairs t-tests and ANCOVA, groups were compared on several SKI measures, including the number of unique responses generated for each problem scenario, the quality of those responses, and the ability to select the best response from a set of alternatives. When equated for socioeconomic status (SES), ABI and control participants performed similarly on the SKI; however, a trend for children with ABI to generate more assertive responses was observed. Performance on the SKI was positively correlated with IQ and related to parent-reported adaptive behavior. In children with ABI, performance was also related to primary lesion location and treatment regimen. CONCLUSIONS: Children with ABI are as capable of judging the appropriateness of behavior and generating response options on an analog measure of social problem solving as were their typically developing peers. However, those individual children with ABI who are more likely to have social problems may be identified by the qualitative aspects of their responses on analog tasks. These findings have implications for the identification of children with social skills deficits following ABI and for the development of effective rehabilitation strategies.

Use of passive surveillance data to study temporal and spatial variation in the incidence of giardiasis and cryptosporidiosis.

OBJECTIVE: The goal of this study was to evaluate temporal and spatial variations in the reporting of cases of giardiasis and cryptosporidiosis to a passive surveillance system, and to assess the relationship of those variations to source of drinking water, adjusting for socioeconomic variables. METHODS: The authors analyzed temporal and spatial patterns for 4,058 cases of giardiasis and 230 cases of cryptosporidiosis reported to the Massachusetts Department of Public Health for 1993-1996. They linked each reported case to a database containing information on source of residential water supply and socioeconomic characteristics and evaluated the association between these factors and reporting rates using regression techniques. RESULTS: Reports of giardiasis and cryptosporidiosis were highest for the mixed unfiltered drinking water supply category. Reports of giardiasis were associated with income levels. Increases in reporting for both giardiasis and cryptosporidiosis were seen in summer to early fall. During a suspected outbreak of cryptosporidiosis n the city of Worcester in 1995, a significant increase in reported cases was also observed in the Boston metropolitan area. Following the suspected outbreak, weekly giardiasis rates increased slightly in Worcester and the Boston metropolitan area, while reporting of cryptosporidiosis increased dramatically. CONCLUSIONS: Consistently collected passive surveillance data have the potential to provide valuable information on the temporal variation of disease incidence as well as geographic factors. However, passive surveillance data, particularly in the initial period of surveillance, may be highly sensitive to patterns of diagnosis and reporting and should be interpreted with caution.

Estimation of Markov random field prior parameters using Markov chain Monte Carlo maximum likelihood.

Recent developments in statistics now allow maximum likelihood estimators for the parameters of Markov random fields (MRFs) to be constructed. We detail the theory required, and present an algorithm that is easily implemented and practical in terms of computation time. We demonstrate this algorithm on three MRF models--the standard Potts model, an inhomogeneous variation of the Potts model, and a long-range interaction model, better adapted to modeling real-world images. We estimate the parameters from a synthetic and a real image, and then resynthesize the models to demonstrate which features of the image have been captured by the model. Segmentations are computed based on the estimated parameters and conclusions drawn.

Parent assessment of psychological and behavioral functioning following pediatric acquired brain injury.

OBJECTIVE: Compare the measured prevalence rate of psychopathology and behavior disorders in 29 children with acquired brain injuries using four parent-report instruments. METHOD: Two questionnaires, the Child Behavior Checklist (CBCL) and the Personality Inventory for Children (PIC-R) and two interview measures, the Diagnostic Interview for Children and Adolescents (DICA-R) and the Vineland Adaptive Behavior Scales (VABS), were completed following injury or diagnosis. RESULTS: The DICA-R identified the highest prevalence of anxiety disorders and acting-out behaviors, whereas the CBCL identified the lowest prevalence. Opposite results were found within the domain of attentional problems. Interview measures were more concordant for global psychological impairment than were questionnaires. DISCUSSION: Discordant findings across measures are discussed in terms of type of disorder, classification model, response format, item characteristics, and scaling.

Carbon monoxide and hospital admissions for congestive heart failure: evidence of an increased effect at low temperatures.

The combined effects of carbon monoxide and low temperature on daily variation in hospital admissions for congestive heart failure (CHF) were examined for a 4-year period in Chicago, Illinois. Medicare hospital admissions for CHF were analyzed as a function of the maximum hourly temperature, maximum hourly levels of carbon monoxide (CO), and other criteria pollutants in Chicago for each day of the 4-year period (1986-1989). The regression analyses for the time series were conducted using single and multipollutant models with interaction terms and adjustments for weather, weekly cycles, seasonal effects, and secular trend. The data were also grouped into three temperature ranges, <40 degrees, 40 degrees-75 degrees, and >75 degrees F, and the relationship between CO and CHF admissions was evaluated for each range. For the 4-year time series, the CO level was positively associated with hospital admissions for CHF in the single pollutant and multipollutant models after adjustment for seasonal effects and weather pattern. The relative risks of hospital admissions for CHF in Chicago associated with the 75th percentile of exposure to CO in the high, medium, and low temperature ranges were 1.02 [95% confidence interval (CI), 0.95-1.10], 1.09 (CI, 1.04-1.14), and 1.15 (CI, 1.09-1.22), respectively. In these data, the effect of CO on hospital admissions for CHF was temperature dependent, with the magnitude of the effect increasing with decreasing temperature. This synergy may help to explain the association between ambient CO and CHF admissions demonstrated in other studies.

Did Milwaukee experience waterborne cryptosporidiosis before the large documented outbreak in 1993?

The patterns of incidence and pathways of spread for cryptosporidiosis are poorly understood. In this study, we explored the possibility that drinking water caused significant waterborne cryptosporidiosis in Milwaukee well before the massive documented outbreak in April 1993. We generated time series of daily counts of emergency room visits and hospital admissions for gastroenteritis in Milwaukee using the billing records of the Medical College of Wisconsin for January 1, 1992, through May 3, 1993. The Milwaukee Water Works provided us with data on drinking water turbidity for the same period. The service area of the South Plant experienced a sharp rise in turbidity just before the outbreak. During the outbreak period, gastroenteritis events were most strongly associated with turbidity at a lag of 7 days in children and 8 days in adults. It is reasonable to conclude that these lag times reflect the incubation period of Cryptosporidium. During the 434 days before the outbreak, gastroenteritis events were most strongly associated with turbidity at a lag of 8 days among children and 9 days among adults in the service area of the North Plant, the plant that experienced the highest effluent turbidity during this period. These findings are consistent with the conclusion that waterborne cryptosporidiosis was occurring in Milwaukee for more than a year before the documented outbreak.

Cognitive-behavioral remediation of problem solving deficits in children with acquired brain injury.

The inability to problem solve can have a deleterious impact on a student's academic performance and social adjustment. Children with an acquired brain injury (ABI) are at risk for deficits in problem solving skills. This case study and series of multiple baseline experiments examined the effects of a multi-component cognitive-behavioral training program on the remediation of problem solving deficits in five children with ABI. Results indicated that the training program resulted in a substantial decrease in errors on a computerized problem solving task used to monitor problem solving performance during baseline and treatment. In addition, significant improvements were found on two of four standardized measures of problem solving abilities. Finally, students, parents and teaching staff reported a high degree of satisfaction with and generalization of the training program.

Additive impact of in-hospital cardiac arrest on the functioning of children with heart disease.

OBJECTIVE: This study examined the impact of a sudden cardiac arrest (CA) on the neurodevelopmental and adaptive functioning of young children with congenital heart disease (CHD). METHODOLOGY: Sixteen children with CHD who had sustained an in-hospital CA were compared with a medically similar group of children with CHD who had not incurred a CA. The contribution of CA, disease severity, and family socioeconomic status on the prediction of developmental outcome variables was evaluated. RESULTS: Children in the CA group displayed more impairments in general cognitive, motor, and adaptive behavior functioning as well as greater disease severity as measured by a cumulative medical risk index. With respect to all children in the study, a higher socioeconomic status was related to higher scores on cognitive functioning, lower levels of child maladjustment, and lower levels of stress within the parent-child relationship. Although the occurrence of a CA alone did not contribute to the prediction of outcome measures, a significant interactional effect between CA and cumulative medical risk index was found. Specifically, among children who had incurred a CA, as disease severity increased, decrements in abilities were observed. Few significant correlations between specific CA-related variables (eg, length of CA) and outcome indices were found. CONCLUSIONS: Results from this study indicate that the impact of cardiac arrest on neuropsychological functioning may be mediated by the child's overall disease severity. These findings have implications for the identification of CA survivors at greatest risk for developmental difficulties.

Breast-conserving therapy vs mastectomy in early-stage breast cancer: a meta-analysis of 10-year survival.

BACKGROUND: The randomized trials comparing breast-conserving therapy (BCT), i.e., surgery and radiation to the breast, with mastectomy in early-stage breast cancer use a variety of protocols. Meta-analysis may assist in understanding the impact of these differences on survival. PURPOSE: To evaluate the possible variations of the relative efficacy of BCT and mastectomy in terms of overall survival according to tumor size, nodal status, and use of adjuvant radiation therapy. METHODS: The most recent published results and, where available, updated patient-level data from randomized controlled trials of BCT and mastectomy for early-stage breast cancer were combined in a meta-analysis using a random effects model. Pooled survival rates and odds ratios were generated according to subgroups of nodal status and tumor size. Five- and 10-year odds ratios were also determined according to adjuvant radiation protocol. RESULTS: The pooled odds ratio comparing 10-year survival for BCT and mastectomy was 0.91. The odds ratios comparing the two treatment regimens were not significant after grouping according to tumor size and nodal status. When more than 50% of node-positive patients in both the mastectomy and BCT arms received adjuvant radiation, both arms had similar survival rates. When less than 50% of node-positive patients in both arms received adjuvant nodal radiation, the odds ratio was 0.69, and patients receiving BCT had a survival advantage. CONCLUSIONS: Patients allocated to BCT have survival rates at least as high as patients allocated to mastectomy. When all protocols were combined, nodal status and tumor size did not significantly alter the relative survival rates. However, under some conditions, particularly for node-positive patients, BCT may confer a relative survival advantage over mastectomy. In particular, mastectomy without adjuvant radiation appears to be inferior to BCT for node-positive patients.

Childhood asthma surveillance using computerized billing records: a pilot study.

OBJECTIVE: This paper describes a pilot project to develop and implement a low-cost system for ongoing surveillance of childhood asthma in Milwaukee County, Wisconsin. METHODS: The authors organized a planning workshop to solicit information and ideas for an asthma surveillance system, bringing together national experts with Milwaukee professionals and community representatives involved in the prevention and treatment of asthma. Based on recommendations from the workshop, a pilot surveillance project was implemented in Milwaukee County using records of emergency room visits and hospital admissions for asthma abstracted from the computerized billing records of the Children's Hospital of Wisconsin (CHW), retrospectively for 1993 and prospectively for 1994. Retrospective data were also sought from the other hospital emergency departments in Milwaukee County to evaluate the representativeness of the CHW data. Surveillance data were used to evaluate utilization of care by patient subgroups and to describe temporal patterns in emergency room visits. RESULTS: Of the emergency department visits for asthma in Milwaukee County in 1993, CHW accounted for 94% among infants less than 1 year of age, 89% among children ages 1 through 5 years, and only 59% among children between the ages of 6 and 18 years. In 1994, the 7% of asthmatic children with repeat hospital admissions accounted for 38% of all hospital admissions for asthma and the 20% with repeat emergency department visits accounted for 50% of all emergency visits. Emergency visits for asthma showed clear seasonality, with a peak in the fall and a smaller peak in the spring. CONCLUSIONS: Computerized medical billing data provide an opportunity for asthma surveillance at a relatively low cost. The data obtained are useful for tracking trends in exacerbations of asthma and the use of medical services for asthma care and should prove valuable in targeting interventions.