In Flint, Mich., the prevalence of elevated blood lead levels rose among children under age 6 years after the switch in the city’s water source, dropped after an advisory was issued, and then dropped below original levels after the city switched back to its original water source, according to the Centers for Disease Control and Prevention.

In the year before the switch (April 25, 2013, to April 24, 2014), 3.1% of blood lead levels (BLLs) in children under age 6 years were 5 mcg/dL or higher, which the CDC considers to be elevated. After the switch from the Detroit Water Authority (DWA) to the Flint Water System (FWS) but before the water advisory was issued (April 25, 2014, to Jan. 2, 2015), elevated BLLs increased to 5.0%, for an adjusted odds ratio of 1.46 (MMWR 2016 Jun 24;65:1-5).

For the period after the water advisory but before the water supply was switched back to the DWA (Jan. 3, 2015, to Oct. 15, 2015), 3.9% of BLLs were elevated (aOR, 1.28). For the 5 months after the switch back to the DWA, the percentage of elevated BLLs dropped to 1.4% (aOR, 0.75).

The analysis involved the results of 9,422 tests received by 7,306 children, all of whom lived in the area served by the FWS. The Environmental Protection Agency recently advised that it is safe for Flint residents to drink filtered tap water and that unfiltered tap water can be used for bathing and showering, the CDC report noted.