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Office of Border Health

Pediatric Lead Assessment on the United States-Mexico Border

In response to a request from the states of Arizona and Sonora, Mexico to document and prevent childhood lead poisoning along the U.S. Mexico border, between March 24 and April 1,1998, we conducted a pediatric blood lead assessment on the Arizona-Sonora border region in the cities of Agua Prieta and San Luis Rio Colorado in the state of Sonora and in the Yuma County, Arizona, cities of San Luis, Somerton, Yuma, Orange Grove, Wellton and Dateland. In each city we chose a sampling site at a health fair, kindergarten, or Women, Infants and Children (WIC) clinic. We formed teams with local professional (nurses, doctors) and lay health care workers (promotoras). These teams received extensive training on how to obtain a fingerstick blood sample and how to operate a portable blood lead analyzer.

Each parent or guardian of a participant completed a demographic and risk-factor questionnaire as well as a consent form. We collected 50uL of blood and analyzed the samples using a portable blood analyzer (LeadCare, Inc.®, Chelmsford, MA). In the Mexican study areas, we obtained an additional drop of blood in order to measure hemoglobin levels using a portable analyzer (HemoCue, Inc.®, Angelholm, Sweden).

A total of 1,517 children participated in the assessment: 453 from Agua Prieta, 561 from San Luis Rio Colorado, and 503 from Yuma County. Eighty-five percent of the participants were Hispanic, and 50% were female. Their mean age was 5.2 years. We conducted blood lead analyses on 93% of the participants. Ninety-nine participants had BLLs below the detection limit (1.4uL/dL). For data analysis purposes, values below the detection limit were considered to be 0.7uL/dL. The overall mean blood level was 5.1ug/dL. Yuma County participants had a significantly lower mean BLL than participants in either of the other two study areas (3.7 ug/dL vs. 6 ug/dL and 5.6ug/dL for Agua Prieta and San Luis Rio Colorado, respectively). Categorizing BLLs according to the CDC guidelines, we found that 94% of the participants had BLLs ≤9.9ug/dL, and 6% had BLL's from 10.0 to 19.9. Only six children had BLLs ≥20ug/dL. The children who had BLLs ≥20ug/dL were immediately referred to the local public health authorities who promptly followed up with additional diagnostic testing and environmental interventions.

The geometric mean blood levels of the assessed population were slightly higher than results from the second phase of the Third National Health and Nutrition Examination Survey (NHANES III, phase 2). Furthermore, the mean for the 6-to-11-year age group was higher than for the 3-to-5-year olds age group, whereas NHANES data show a higher rate for the 3-5-year olds than for the 6-to-11-year-olds. The difference in trends suggests different exposure patterns in this border region than in most of the U.S.

We conclude from our investigation that the blood levels of children in this area of the U.S.-Mexico border region do not appear to be a major public health problem. The low prevalence of elevated BLLs documents the success of lead-reduction programs in the community. Nevertheless, the children with blood levels ≥10ug/dL are of concern. Continued and focused surveillance based on risk factors is important to identifying children with elevated blood lead levels and responding rapidly so that their exposure can be reached as quickly as possible. Community education on ways to reduce or eliminate lead exposure should be continued.

For a complete version of this report please contact our office.