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Targeted Screening for Childhood Lead Exposure in a Low Prevalence Area Salt Lake County, Utah, 1995 1996

During 1991-1994, an estimated 930,000 U.S. children aged less than 6 years had blood lead levels (BLLs) greater than or equal to 10 ug/dL, and the risk for an elevated BLL was greatest among children who were non-Hispanic black or Mexican American, from low-income families, living in large metropolitan areas, or living in housing built before 1946 (1). Because risk for lead exposure is associated with several different factors, it can vary greatly across relatively small areas. To establish the local prevalence and distribution of childhood lead exposure and develop local blood lead screening recommendations, the Salt Lake City-County Health Department (SLCCHD) offered free blood lead screening to all children aged 12-36 months enrolled at the seven Special Supple-mental Nutrition Program for Women, Infants, and Children (WIC) clinics in Salt Lake County, Utah (1995 population: 812,000), during January-October 1995. This report presents findings of the screenings at WIC clinics, describes the design and promotion of local targeted screening recommendations, and describes the resulting increases in appropriate BLL screenings among children.

WIC Prevalence Survey

The seven WIC clinics are dispersed throughout Salt Lake County. Parents or guardians for 5168 (96.6%) of 5350 children aged 12-36 months enrolled in the WIC clinics provided written consent for screening. Screening was done by capillary blood sampling onto filter paper (FP), which was dried and tested for lead with atomic absorption spectrophotometry (2). The geometric mean BLL was 2.9 ug/dL. BLLs were greater than or equal to 10 ug/dL for 93 (1.8%) children, greater than or equal to 15 ug/dL for 25 (0.5%), and greater than or equal to 20 ug/dL for seven (0.1%).

Parents or guardians for 21 of the 25 children with screening BLLs greater than or equal to 15 ug/dL agreed to have confirmatory venous sampling and simultaneous repeat FP blood sampling (performed 13-103 days after screening). Venous BLLs ranged from 2 ug/dL to 36 ug/dL; nine were greater than or equal to 15 ug/dL. Repeat FP BLLs ranged from 4 ug/dL to 40 ug/dL; six were greater than or equal to 15 ug/dL. Correlation between the simultaneously drawn FP and venous samples was high (Spearman R=0.94), although the FP BLL averaged 1.5 ug/dL lower than the venous BLL (range: 9 ug/dL lower to 4 ug/dL higher).

Twelve (66.7%) of the 18 children with screening BLLs 15-19 ug/dL and all seven children with screening BLLs greater than or equal to 20 ug/dL resided in a small area of central Salt Lake City (Figure_1). Environmental assessments by the SLCCHD for the seven children with BLLs greater than or equal to 20 ug/dL established the probable source of exposure for five children as deteriorating lead-based paint in their homes; for the other two children, no probable source of exposure was identified.

Design and Promotion of Screening Recommendations

The prevalence of BLLs greater than or equal to 10 ug/dL among WIC screening survey participants varied from 0-6% by zip code area among the 25 (of 34) local zip code areas from which at least 50 children were sampled. SLCCHD used the geographic clustering of elevated BLLs and U.S. census housing data to design a screening "target area" centered around the homes of children in the cluster and extending to adjacent areas of older housing. The target area, bordered by major streets and natural boundaries, included all or nearly all of five zip code areas and smaller portions of an additional five zip code areas. It included approximately 23 square miles (960 square city blocks), representing approximately 10% of the inhabited land and 15% of the population of the county (3). The target area had a much higher prevalence of houses built before 1950 (55.4%) than the remainder of the county (10.3%) (3). Two of the seven WIC clinics were located within the target area. Among WIC participants aged 12-36 months screened during 1995, the prevalence of BLLs greater than or equal to 10 ug/dL was 4.8% in the target area and 1.2% outside the target area.

In October 1995, SLCCHD mailed a summary of the WIC screening results to private physicians providing primary care to children in the Salt Lake City area (n=327) (compiled from the member roster of the Utah Medical Association and listings in the local telephone book). These physicians were encouraged to begin one-time, office-based blood lead screening as part of routine well-child care for all children aged 6-36 months living in the target area and to screen children living outside the target area who were potentially at greater risk for lead exposure. Identification of children at greater risk was based on responses to a modified CDC questionnaire (4) that asked about residence in a home built before 1960 that had deteriorating paint or was being remodeled, household members with work- or hobby-related lead exposures, elevated BLL identified in a household member, and recent residence in the target area. In addition, all 32 pediatricians and family-practice physicians with offices in the target area were visited by SLCCHD staff, who presented the rationale for and the logistics of office-based screening and described the support available from SLCCHD for screening and follow-up of children with BLLs greater than or equal to 20 ug/dL (5,6). On completion of the physician visits in July 1996, a mass mailing advising screening for children aged 12-36 months was sent to all households within the 10 zip code areas that were at least partially within the target area.

Targeted Screening Results

Information about the number of blood lead screening tests performed and the BLLs of those screened are provided to the SLCCHD by laboratories providing blood lead testing for Salt Lake County. Following the promotion of the new screening recommendations, private-sector, office-based blood lead screening increased significantly (p less than 0.05) within both the target area and the nontarget area. For example, during January-March 1996, an average of 11 children (including three children in the target area) aged 12-36 months were screened per month, compared with 88 children (including 57 children in the target area) per month during August-December 1996.

During August-December 1996, a total of 284 (approximately 7%) children in the target area were screened; 21 (7.4%) had BLLs greater than or equal to 10 ug/dL. Among the 154 children outside the target area also screened during this period, nine (5.8%) had BLLs greater than or equal to 10 ug/dL. Four children in the target area had BLLs greater than or equal to 20 ug/dL; on environmental investigation, all elevated BLLs were determined to be related to leaded paint in the child's home. One child not in the target area had a BLL greater than or equal to 20 ug/dL related to a parent's occupational exposure.

Reported by: TL Schlenker, MD, I Risk, MPA, H Harris, Salt Lake City-County Health Dept, Utah. Lead Poisoning Prevention Br, Div of Environmental Hazards and Health Effects, National Center for Environmental Health, CDC.

Editorial Note

Editorial Note: Lead is an environmental toxicant with serious adverse effects on children's behavior and development, which can range from decreased growth, hearing, and intelligence at low exposures to encephalopathy and death at high exposures (4). BLLs at least as low as 10 ug/dL can adversely affect the health of children, and the higher the BLL, the greater the risk (4). CDC generally recommends that children first receive blood lead screening at age 1 year but has recommended screening high-risk children as early as age 6 months (4). To address elevated BLLs in children, CDC guidelines recommend 1) nutritional and educational interventions for children identified with BLLs 10-19 ug/dL, 2) environmental evaluation to identify lead hazards for children with BLLs greater than or equal to 20 ug/dL or with BLLs that persist at greater than or equal to 15 ug/dL, and 3) medical evaluation and intervention for children with BLLs greater than or equal to 20 ug/dL (4).

National data have demonstrated consistent declines in average BLLs in the United States for all age groups since the late 1970s, mainly attributed to bans on the use of lead in household paint, gasoline, food and drink cans, and plumbing systems (1,7,8). Public health efforts to prevent childhood lead poisoning, lead paint-abatement programs, and the promulgation of a standard for lead exposure in industry probably also have served to decrease lead exposure for some groups in the United States. Nonetheless, many children in the United States continue to be exposed to lead, primarily through house dust and soil contaminated with lead from deteriorated lead-based paint in older homes and residual lead fallout from vehicle exhaust (4). Other exposure sources can include lead and lead dust brought into the home from household members' workplaces or hobbies, lead contained in some "traditional" (i.e., "folk") medicines and cosmetics, and lead that leaches into water or food from plumbing and crystal and ceramic containers (4).

The findings in Salt Lake County demonstrate how evaluation of the local distribution of childhood lead exposure risk, targeting of services to those at greatest risk, and outreach to the public and to health-care providers can be combined effectively to reach children who require BLL screening. The proportions of children identified with elevated BLLs in the target area and outside the target area were comparable, which may indicate that the children not in the target area were selected appropriately for screening based on responses to the questionnaire.

Venipuncture is the most accurate sampling method for BLL testing and the only method for confirming an elevated BLL, but fingerstick blood collected with capillary tubes is sufficiently accurate for screening when hands are carefully cleaned to avoid contaminating samples with lead dust on the skin surface (6). CDC is evaluating fingerstick blood collected onto FP to determine how accurately blood lead is measured using this method. The overall accuracy of FP sampling in the SLCCHD study cannot be determined because not all children received simultaneous FP and venous BLL tests.

In 1991, CDC recommended universal screening of children aged less than 6 years except in communities where the prevalence of elevated BLLs is known to be very low (4) and therefore is not a practical or cost-beneficial investment of limited resources. As the prevalence of elevated BLLs continues to diminish in the United States, targeting screening to children who remain at elevated risk for lead exposure will become increasingly important. The risk for childhood lead exposure can vary even within a small geographic area, as indicated by the findings in Salt Lake County. Therefore, CDC is developing guidelines to help state and local health departments determine whether to recommend universal or targeted screening within their jurisdictions and communicate those recommendations to the public and to pediatric health-care providers. A draft of these guidelines is available for public review and comment until April 7, 1997; copies can be obtained by calling (888) 232-6789 or accessing the World-Wide Web at http://www.cdc.gov/nceh.

References

  1. CDC. Update: blood lead levels -- United States, 1991-1994. MMWR 1997;46:141-6.

  2. Verebey K, Eng YM, Davidow B, Ramon A. Rapid, sensitive micro blood lead analysis: a mass screening technique for lead poisoning. J Anal Toxicol 1991;15:237-40.

  3. Bureau of the Census. 1990 Census of population and housing: population and housing characteristics for census tracts and block numbering areas -- Salt Lake City-Ogden, Utah MSA. Washington, DC: US Department of Commerce, Economics, and Statistics, Bureau of the Census, 1993; report no. 1990 CPH-3-290.

  4. CDC. Preventing lead poisoning in young children: a statement by the Centers for Disease Control. Atlanta, Georgia: US Department of Health and Human Services, Public Health Service, 1991.

  5. Schlenker TL, Fritz CJ, Murphy A, Shepeard S. Feasibility and effectiveness of screening for childhood lead poisoning in private medical practice. Arch Pediatr Adolesc Med 1994;148: 761-4.

  6. Schlenker TL, Fritz CJ, Mark D, et al. Screening for pediatric lead poisoning: comparability of simultaneously drawn capillary and venous blood samples. JAMA 1994;271:1346-8.

  7. Annest JL, Pirkle JL, Makuc D, Neese JW, Bayse DD, Kovar MG. Chronological trend in blood lead levels between 1976 and 1980. N Engl J Med 1983;308:1373-7.

  8. Pirkle JL, Brody DJ, Gunter EW, et al. The decline in blood lead levels in the United States: the National Health and Nutrition Examination Surveys (NHANES). JAMA 1994;272:284-91.



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