Sierra Vista located in Arizona has had at least a dozen children that have developed leukemia since 1997 and at least two have died of it. This is nearly triple the childhood leukemia rate expected in a town of 40,000 during that time period. A three year study by federal health officials said that they detected no toxic exposures that could have caused the illnesses.

Beverly Kingsley, an epidemiologist with the federal Centers for Disease Control and Prevention, stated " We don't know why this cluster occurred. We really wish we had the answer, but we don't"

In 2004, the CDC decided to draw and analyze samples of blood, urine and cheek swabs from the surviving patients and their families. They tested them for 128 different contaminants including toxic chemicals, metals, pesticides and volatile organic compounds. They compared these samples with healthy children from Sierra Vista. The samples also underwent genetic testing.

Environmental toxins have long been suspected as a trigger of leukemia, only one though, benzene has ever been proven to cause it. Some of the town people feel they have attended too many funerals and feel that something has to be going on. The townspeople also said in a meeting that the CDC held that the study did not include enough patients, didn't span a long enough period of time and also didn't include environmental testing for toxins.