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Environmental exposure to lead and children's intelligence at the age of seven years
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Abstracts from the literature
Comment: Concerns about the influence of medication on learning ability and behavior are commonly expressed by parents of children with asthma. In this study, 28% of parents reported that their children had disease- or therapy-related learning problems. This carefully controlled study provides strong evidence that asthma and one commonly used maintenance medication, theophylline, have little influence on well-standardized measures of academic achievement. The results do not imply that severe or poorly controlled asthma or other medications cannot have shortterm adverse effects on behavior and school performance. However, when sociodemographic factors are controlled, there is little evidence of the long-term effects of asthma or its treatment on major spheres of development in children with asthma. Jack M. Fletcher, PhD Department of Pediatrics University of Texas Medical School at Houston Houston, TX 77030 Environmental exposure to lead and children's Intelligence at the a g e of seven years Baghurst PA, McMichael A J, Wigg NR, et al. N Engl J Med 1992;327:1279-84.
Objective: To examine the relationship between intelligence at 7 years of age in relation to blood lead levels from before birth (maternal levels) to 7 years of age. Design: Cohort study. Setting: A lead-smelting community in southern Australia. Patients: The original cohort consisted of 723 infants, 90% of the singleton live births for the community from 1979 to 1982. Of the 516 children (71%) Who remain ed in the study at age 7 years, 494 Were examined. Patients lost to follow-up were similar in 12 o f l 5 variables, including umbilical cord blood le~/els. Interventions: Blood lead levels were measured before delivery, iia cord blood, at the ages of 6 months, 15 months, and years, and annually thereafter. Data were also collected on potential confounding variables, including socioeconomicstatus, the caregiving environment, maternal intelligence, parental smoking habits, parental education, birth weight and birth order, and duration of breast-feeding. ~tain outcome measures: The primary study outcome was intelligence at age 7 years, as measured by the Wechsler Intelligence Scale for Children--Revised (WISC-R). Measurements were made by one psychologist, who was unaware of the children's lead levels. Results: Blood lead levels varied from 4.3 to 15/~g/dl (lowest and highest quartile averages) in umbilical samples, to 11.8 to 34.4 tag/dl at age 15 months. By age 7 years, the range was 6.6 to 20.0 ttg/dl. After adjustment for confounding variables, there was a consistent, significant rela-
The Journal of Pediatrics May 1993 tionship between blood lead levels at age 15 months to 4 years and IQ at age 7 years. Using adjusted coefficients of variation, the authors estimated that, for an increase in blood lead concentration from 10 to 30 ttg/dl at age 3 years, there is a decrement of 7.8 IQ points for girls and 2.6 points for boys. Conclusions: Lead exposure during early childhood, even at relatively low levels, is inversely associated with neuropsychologic development through the first 7 years of life.
Comment: In 1984 an estimated 17% (3 to 4 million) of all preschool children in the United States had whole blood lead concentrations greater than 15 ttg/dl. This study adds significantly to a large amount of information already published that documents persistent adverse effects of low to moderate blood lead levels on intellectual functioning. This study suggests that the age range of 15 months to 4 years is the period of most susceptibility for longer-term adverse effects on intellectual functioning. On the basis of national studies, in the average pediatric practice of 3000 children, 15 children with lead levels >25 tag/dl and 90 children with levels >10/~g/dl may be expected. Concerns about an unnecessarily increased work load and the cost-benefit ratio of frequent screenings are being voiced by some pediatricians. The appropriate screening interval (every 6 months? once in the first 6 years? or at ages 1, 2, and 3 years?) and a reasonable definition of low-prevalence communities, which do not need screening as frequently, are needed. Many major pediatric centers are treating children whose lead levels are >25 ~tg/dl with oral administration of the drug succimer in the context ofa postmarketing surveillance study. Although many questions remain unanswered, there is a need to come to a generalpracticai consensus regarding screening and treatment so that the practicing physician has workable guidelines for management of his or her patients. Wayne R. Snodgrass, MD, PhD Departments of Pediatrics and Pharmacology- Toxicology University of Texas Medical Branch Galveston, TX 77550
Duration of symptoms and outcome in baclerial meningitis: An analysis Of causation and the im o plications of a delay in diagnosis Radetsky M. Pediatr Infect Dis J 1992;11:694-8.
Objective: To determine whether a delay in initiating antimicrobial therapy Causes increased risk of sequelae in bacterial meningitis. Study design: Critical review. Data sources: The method of locating relevant articles was not described. Twenty-two articles published from 1962 to 1990 were included.
Abstracts from the literature
Comment: Concerns about the influence of medication on learning ability and behavior are commonly expressed by parents of children with asthma. In this study, 28% of parents reported that their children had disease- or therapy-related learning problems. This carefully controlled study provides strong evidence that asthma and one commonly used maintenance medication, theophylline, have little influence on well-standardized measures of academic achievement. The results do not imply that severe or poorly controlled asthma or other medications cannot have shortterm adverse effects on behavior and school performance. However, when sociodemographic factors are controlled, there is little evidence of the long-term effects of asthma or its treatment on major spheres of development in children with asthma. Jack M. Fletcher, PhD Department of Pediatrics University of Texas Medical School at Houston Houston, TX 77030 Environmental exposure to lead and children's Intelligence at the a g e of seven years Baghurst PA, McMichael A J, Wigg NR, et al. N Engl J Med 1992;327:1279-84.
Objective: To examine the relationship between intelligence at 7 years of age in relation to blood lead levels from before birth (maternal levels) to 7 years of age. Design: Cohort study. Setting: A lead-smelting community in southern Australia. Patients: The original cohort consisted of 723 infants, 90% of the singleton live births for the community from 1979 to 1982. Of the 516 children (71%) Who remain ed in the study at age 7 years, 494 Were examined. Patients lost to follow-up were similar in 12 o f l 5 variables, including umbilical cord blood le~/els. Interventions: Blood lead levels were measured before delivery, iia cord blood, at the ages of 6 months, 15 months, and years, and annually thereafter. Data were also collected on potential confounding variables, including socioeconomicstatus, the caregiving environment, maternal intelligence, parental smoking habits, parental education, birth weight and birth order, and duration of breast-feeding. ~tain outcome measures: The primary study outcome was intelligence at age 7 years, as measured by the Wechsler Intelligence Scale for Children--Revised (WISC-R). Measurements were made by one psychologist, who was unaware of the children's lead levels. Results: Blood lead levels varied from 4.3 to 15/~g/dl (lowest and highest quartile averages) in umbilical samples, to 11.8 to 34.4 tag/dl at age 15 months. By age 7 years, the range was 6.6 to 20.0 ttg/dl. After adjustment for confounding variables, there was a consistent, significant rela-
The Journal of Pediatrics May 1993 tionship between blood lead levels at age 15 months to 4 years and IQ at age 7 years. Using adjusted coefficients of variation, the authors estimated that, for an increase in blood lead concentration from 10 to 30 ttg/dl at age 3 years, there is a decrement of 7.8 IQ points for girls and 2.6 points for boys. Conclusions: Lead exposure during early childhood, even at relatively low levels, is inversely associated with neuropsychologic development through the first 7 years of life.
Comment: In 1984 an estimated 17% (3 to 4 million) of all preschool children in the United States had whole blood lead concentrations greater than 15 ttg/dl. This study adds significantly to a large amount of information already published that documents persistent adverse effects of low to moderate blood lead levels on intellectual functioning. This study suggests that the age range of 15 months to 4 years is the period of most susceptibility for longer-term adverse effects on intellectual functioning. On the basis of national studies, in the average pediatric practice of 3000 children, 15 children with lead levels >25 tag/dl and 90 children with levels >10/~g/dl may be expected. Concerns about an unnecessarily increased work load and the cost-benefit ratio of frequent screenings are being voiced by some pediatricians. The appropriate screening interval (every 6 months? once in the first 6 years? or at ages 1, 2, and 3 years?) and a reasonable definition of low-prevalence communities, which do not need screening as frequently, are needed. Many major pediatric centers are treating children whose lead levels are >25 ~tg/dl with oral administration of the drug succimer in the context ofa postmarketing surveillance study. Although many questions remain unanswered, there is a need to come to a generalpracticai consensus regarding screening and treatment so that the practicing physician has workable guidelines for management of his or her patients. Wayne R. Snodgrass, MD, PhD Departments of Pediatrics and Pharmacology- Toxicology University of Texas Medical Branch Galveston, TX 77550
Duration of symptoms and outcome in baclerial meningitis: An analysis Of causation and the im o plications of a delay in diagnosis Radetsky M. Pediatr Infect Dis J 1992;11:694-8.
Objective: To determine whether a delay in initiating antimicrobial therapy Causes increased risk of sequelae in bacterial meningitis. Study design: Critical review. Data sources: The method of locating relevant articles was not described. Twenty-two articles published from 1962 to 1990 were included.