Lethality of firearms relative to other suicide methods: a population based study.

OBJECTIVES: (1) To quantify lethality of firearms relative to other suicide methods, (2) to quantify the extent to which suicide mortality may be reduced by limiting access to firearms. METHODS: Data on suicides and hospitalised para-suicides that occurred in the state of Illinois from 1990 to 1997 were combined. Total number of episodes for each suicide method was estimated as the sum of the number of suicides and the number of para-suicides for that method. Gender and suicide method were used as proxies for intention to die, and estimated lethality of suicide methods within method-gender groups (for example, male firearm users). Logistic regression was used to quantify the lethality of firearms relative to other suicide methods. Excess mortality associated with the use of firearms was estimated by conservatively assuming that in the absence of firearms the next most lethal suicide method would be used. RESULTS: From January 1990 to December 1997, among individuals 10 years or older in the state of Illinois, there were 37,352 hospital admissions for para-suicide and 10,287 completed suicides. Firearms are the most lethal suicide method. Episodes involving firearms are 2.6 times (95% CI 2.1 to 3.1) more lethal than those involving suffocation-the second most lethal suicide method. Preventing access to firearms can reduce the proportion of fatal firearms related suicides by 32% among minors, and 6.5% among adults. CONCLUSIONS: Limiting access to firearms is a potentially effective means of reducing suicide mortality.

Statistical inference in a two-compartment model for hematopoiesis.

We present a method for parameter estimation in a two-compartment hidden Markov model of the first two stages of hematopoiesis. Hematopoiesis is the specialization of stem cells into mature blood cells. As stem cells are not distinguishable in bone marrow, little is known about their behavior, although it is known that they have the ability to self-renew or to differentiate to more specialized (progenitor) cells. We observe progenitor cells in samples of bone marrow taken from hybrid cats whose cells contain a natural binary marker. With data consisting of the changing proportions of this binary marker over time from several cats, estimates for stem cell self-renewal and differentiation parameters are obtained using an estimating equations approach.

Ozone uptake in the intact human respiratory tract: relationship between inhaled dose and actual dose.

Inhaled concentration (C), minute volume (MV), and exposure duration (T) are factors that may affect the uptake of ozone (O(3)) within the respiratory tract. Ten healthy adult nonsmokers participated in four sessions, inhaling 0.2 or 0.4 ppm O(3) through an oral mask while exercising continuously to elicit a MV of 20 l/min for 60 min or 40 l/min for 30 min. In each session, fractional absorption (FA) was determined on a breath-by-breath basis as the ratio of O(3) uptake to the inhaled O(3) dose. The mean +/- SD value of FA for all breaths was 0.86 +/- 0.06. Although C, MV, and T all had statistically significant effects on FA (P < 0.0001, P = 0.004, and P = 0.026, respectively), the magnitudes of these effects were small compared with intersubject variability. For an average subject, a 0. 05 change in FA would require that C change by 1.3 ppm, MV change by 46 l/min, or T change by 1.7 h. It is concluded that inhaled dose is a reasonable surrogate for the actual dose delivered to a particular subject during O(3) exposures of <2 h, but it is not a reasonable surrogate when comparisons are made between individuals.

Children in Illinois with elevated blood lead levels, 1993-1998, and lead-related pediatric hospital admissions in Illinois, 1993-1997.

OBJECTIVE: This study uses screening and hospitalization data to describe the prevalence of childhood lead poisoning in Chicago and the rest of the state of Illinois. METHODS: The authors used aggregate data published by the Illinois Department of Public Health on blood lead testing of children ages 0-6 years and data on lead-related hospital admissions of children ages 0-6 years, drawn from an administrative dataset compiled as part of a state initiative. RESULTS: No clear time trends in the percentage of children with elevated blood lead levels (defined as >15 micrograms per deciliter [microg/dL] or >45 microg/dL) were evident in either Chicago or the rest of Illinois. The proportions of children with elevated blood lead levels in Chicago and in the rest of Illinois did not decline at the dramatic rate seen in the US as a whole during the 1990s. Over a five-year period, in-hospital charges of $7.7 million were generated for the care of lead-poisoned children ages 6-16 in Chicago alone. CONCLUSION: Surveillance data, analyzed at the appropriate geographic level, can be used to focus resources on high-risk areas and to evaluate prevention efforts.

An X chromosome gene regulates hematopoietic stem cell kinetics.

Females are natural mosaics for X chromosome-linked genes. As X chromosome inactivation occurs randomly, the ratio of parental phenotypes among blood cells is approximately 1:1. Recently, however, ratios of greater than 3:1 have been observed in 38-56% of women over age 60. This could result from a depletion of hematopoietic stem cells (HSCs) with aging (and the maintenance of hematopoiesis by a few residual clones) or from myelodysplasia (the dominance of a neoplastic clone). Each possibility has major implications for chemotherapy and for transplantation in elderly patients. We report similar findings in longitudinal studies of female Safari cats and demonstrate that the excessive skewing that develops with aging results from a third mechanism that has no pathologic consequence, hemizygous selection. We show that there is a competitive advantage for all HSCs with a specific X chromosome phenotype and, thus, demonstrate that an X chromosome gene (or genes) regulates HSC replication, differentiation, and/or survival.

Strategies for hematopoietic stem cell gene therapy: insights from computer simulation studies.

We simulated gene therapy using parameters derived from the analysis of autologous transplantation studies in glucose-6-phosphate dehydrogenase heterozygous cats to determine how hematopoietic stem cell (HSC) biology might influence outcomes. Simulation illustrates that a successful experiment can result by chance and may not be the repeated outcome of a specific protocol design or technical approach. As importantly, in many simulated gene therapy experiments where 1, 2, or 6 of 30 transplanted HSC were labeled, there was significant variation in the contribution from marked clones over time. Variability was minimized in simulations in which large numbers of HSC were transplanted. Strategies that may permit consistent clinically successful results are presented. Taken together, these simulation studies demonstrate that the in vivo behavior of HSC must be considered when optimizing approaches to gene therapy in large animals, and perhaps by extension, in humans.

Evidence that hematopoiesis may be a stochastic process in vivo.

To study the behavior of hematopoietic stem cells in vivo, hematopoiesis was simulated by assuming that all stem cell decisions (that is, replication, apoptosis, initiation of a differentiation/maturation program) were determined by chance. Predicted outcomes from simulated experiments were compared with data obtained in autologous marrow transplantation studies of glucose 6-phosphate dehydrogenase (G6PD) heterozygous female Safari cats. With this approach, we prove that stochastic differentiation can result in the wide spectrum of discrete outcomes observed in vivo, and that clonal dominance can occur by chance. As the analyses also suggest that the frequency of feline hematopoietic stem cells is only 6 per 10(7) nucleated marrow cells, and that sem cells do not replicate on average more frequently than once every three weeks, these large-animal data challenge clinical strategies for marrow transplantation and gene therapy.

Simulation of hematopoiesis: implications for the gene therapy of lysosomal enzyme disorders.

Although the hematopoietic stem cell is an attractive target for gene transfer, little is known about its biology in vivo in large animals (including humans). We have studied the in vivo behavior of hematopoietic stem cells in glucose-6-phosphate dehydrogenase heterozygous (female Safari) cats, and demonstrated that clonal instability persists for up to 4.5 years after autologous marrow transplantation. This contrasts with the 2-6 months of clonal disequilibrium reported in comparable murine studies. Our data also suggest that hematopoietic stem cells do not self-renew more than once every 3 weeks. These data may have relevance for strategies to optimize gene therapy in large animals and, by extension, in humans.

Behavior of hematopoietic stem cells in a large animal.

To study the behavior of hematopoietic stem cells in vivo, we transplanted glucose-6-phosphate dehydrogenase (G6PD) heterozygous (female Safari) cats with small amounts of autologous marrow. The G6PD phenotypes of erythroid burst-forming units and granulocyte/macrophage colony-forming units were repeatedly assayed for 3.5-6 years after transplantation to track contributions of stem cell clones to the progenitor cell compartment. Two phases of stem cell kinetics were observed, which were similar to the pattern reported in comparable murine studies. Initially there were significant fluctuations in contributions of stem cell clones. Later clonal contributions to hematopoiesis stabilized. The initial phase of clonal disequilibrium, however, extended for 1-4.5 years (and not 2-6 months as seen in murine experiments). After this subsided, all progenitor cells from some animals expressed a single parental G6PD phenotype, suggesting that blood cell production could be stably maintained by the progeny of one (or a few) cells. As the hematopoietic demand of a cat (i.e., number of blood cells produced per lifetime) is over 600 times that of a mouse, this provides evidence that an individual hematopoietic stem cell has a vast self-renewal and/or proliferative capacity. The long phase of clonal instability may reflect the time required for stem cells to replicate sufficiently to reconstitute a large stem cell reserve.