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Notice to Readers: Examining the Effect of Previously Missing Blood Lead Surveillance Data on Results Reported in MMWR
During 2000--2003, the District of Columbia (DC) experienced very high concentrations of lead in drinking water. In February 2004, the DC Department of Health requested assistance from CDC to assess health effects of elevated lead levels in residential tap water. CDC reviewed available blood lead surveillance data for the period 1998--2003 and reported the findings of a longitudinal analysis and cross-sectional study in MMWR on April 2, 2004 (1).
A substantial number of blood lead test results from blood specimens collected in 2003 were unavailable for the analysis published in the 2004 MMWR report. In 2009, CDC acquired all known 2003 blood lead test results for DC residents and completed a reanalysis to determine whether the addition of the previously missing tests altered the previously reported results. The complete reanalysis is available at http://www.cdc.gov/nceh/lead/leadinwater.
The reanalysis included the 9,765 tests used in the original analysis, plus 1,753 tests reported in surveillance data after the MMWR report was published, and 12,168 tests that had not been included in the surveillance files. The reanalysis showed that addition of the missing test data led to a decrease in the percentage of tests with elevated blood lead levels ≥5 µg/dL or ≥10 µg/dL in 2003, regardless of the type of service line supplying water to the home (Table). These results do not change CDC's original conclusions that "the percentage of test results ≥10 µg/dL and the percentage of test results ≥5 µg/dL at addresses with lead service pipes were higher than at addresses without lead service pipes."
In the 2004 MMWR report, the first sentence of the Editorial Note referred to a cross-sectional study of homes with very high lead levels in drinking water and stated that "no children were identified with blood lead ≥10 µg/dL, even in homes with the highest water lead levels." This sentence was misleading because it referred only to data from the cross-sectional study and did not reflect findings of concern from the separate longitudinal study that showed that children living in homes serviced by a lead water pipe were more than twice as likely as other DC children to have had a blood lead level ≥10 µg/dL. CDC reiterates here a key message from the 2004 report: "because no threshold for adverse health effects in young children has been demonstrated," no safe blood level has been identified, and all sources of lead exposure for children should be controlled or eliminated. "Lead concentrations in drinking water should be below the U.S. Environmental Protection Agency's action level of 15 ppb."
Reference
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