[Determining factors in lowering blood lead levels below the poisoning threshold in Greater Paris (1992-2006)]

Given the serious health effects of lead poisoning (Pb> or =10microg/dL), the present study was designed to estimate the time required to reach and identify factors associated with reaching Pb<10microg/dL according to the severity of the poisoning.

Since 1992, the Greater Paris lead poisoning monitoring system (SSSILF) has been systematically recording data on blood lead levels of screening and follow-up testing of children in the region. In children under the age of seven when screened positive for lead poisoning, survival curves without reaching the threshold of 10microg/dL and the relative risk (RR) of reaching this threshold were calculated (Kaplan-Meier curves and Cox model), according to blood lead level groups (Group 4: Pb> or =45microg/dL; Group 3: 25microg/dL< or =Pb<45microg/dL; Group 2: 10microg/dL< or =Pb<25microg/dL; (by definition, Group 1: Pb<100microg/L and risk factors of poisoning).

The median survival times without reaching the threshold of Pb<10microg/dL were 72.7 months for Group 4, 36.8 months for Group 3 and 14.5 months for Group 2. Compared to reference categories, the time to Pb<10microg/dL was longer for children aged four and over at the time they screened positive for poisoning (Groups 4 and 3), for children displaying pica behavior (Groups 3 and 2), for children in an environment with another child suffering from lead poisoning (Groups 3 and 2) and for children of mothers from Sub-Saharan or North Africa countries (Group 2); the differences reached statistical significance. Changes in Pb levels were better for all children (Groups 4, 3 and 2) screened over the most recent period, i.e. 2002 to 2006, and for Group 2 children living in Paris or the nearby district of Seine-Saint-Denis.

While the time required has gone down over recent years, the time to reach the threshold of Pb<10microg/dL is counted in years and varies depending on known poisoning risk factors and the district responsible for patient management. It is essential to have early lead poisoning screening for children in high-risk groups and then follow-up after rapid implementation of appropriate medical and social measures.