Dooyema et al. convulsions. Ill children failed to respond to malaria treatment and empiric antibiotics. MSF and State Ministry of Health staff noted that all four villages participated in artisa- nal gold ore–processing activities, and heavy- metal poisoning was considered as a potential source of the illnesses. Venous blood samples, analyzed in Europe, from eight symptomatic children from an affected village indicated BLLs between 168 and 370 µg/dL. These concentrations exceed the U.S. CDC level of concern of 10 µg/dL and are well known to be fatal (CDC 2002). MSF notified Nigerian authorities of the results, and a team of inter- national experts was mobilized to assist in the investigation and response to this outbreak. In this report we describe the response and investigation of an outbreak of childhood lead poisoning with child mortality unprec- edented in modern times. On 8 May 2010, the Nigerian Federal Ministry of Health assembled representatives from federal, state, and international organizations, including the Nigeria Field Epidemiology and Laboratory Training Program, CDC, and WHO, to join in ongoing MSF efforts to investigate and respond to the outbreak. The purpose of this emergency response was to determine the cause and contributing factors to the outbreak and identify and prioritize children < 5 years of age with lead poisoning for emergency chelation therapy. The urgent nature of the response and the limited resources necessi- tated quick investigation and intervention to stop the increasing rate of child fatalities in these villages. Although some adults in these villages were reported to have symp- toms of lead poisoning, initial efforts focused almost entirely on children < 5 years of age. Young children are most susceptible to lead poisoning, and most of the fatalities in MSF clinics were among children < 5 years of age. Investigators hypothesized that the outbreak of lead poisoning was associated with artisanal gold ore–processing activities. Investigators used a three-pronged approach to investigate the outbreak that included a door-to-door survey, blood lead sampling, and environ- mental testing. Methods Cross-sectional survey. Stakeholders, includ- ing Nigerian state health officials and MSF, recommended the two most affected villages (A and B) for participation. The investigation protocol was reviewed and approved by both the Nigerian government and the CDC. The investigation was conducted in accordance with the Declaration of Helsinki developed by the World Medical Association (2008). After obtaining consent of village leaders, investigators conducted a cross-sectional, door- to-door survey from 23 May to 4 June 2010 to interview parents, sample blood from children 602 < 5 years of age, and collect soil from house- holds. Informed consent to administer the sur- vey, draw blood, and collect environmental samples was obtained from the head of the household before survey initiation. Local health professionals and translators were trained in a 4-hr session on survey administration, venous blood drawing, and environmental sampling. Each village consisted of numerous family dwellings separated by low walls. Investigators defined a compound as several multigenera- tional and multifamily dwellings enclosed by a common wall. All compounds in village A were eligible to participate in the survey. Because of time and logistical constraints, only compounds in the central area of vil- lage B were eligible to participate. The central area of village B included most of the com- pounds and common gathering places such as mosques, markets, and the residence of the head of the village. dren < 5 years of age in each compound, includ- ing the number living in the compound, the number with a history of convulsions, the num- ber who had died in the preceding 12 months, and their approximate date of death. Before the investigation, the team heard that artisanal gold ore–processing activities were occurring in both villages. These ore- processing activities included a) breaking rocks into small gravel-size pieces (breaking); b) grinding rocks into a fine powder with a flour mill or mortar and pestle (grinding); c) washing ground ore powder with water to separate gold particles (washing); d) drying ground ore after washing (drying); e) using liquid mercury to amalgamate gold flakes (separating); and f) using heat to vaporize mercury from the gold mixture after amal- gamation (melting). Both men and women in the villages participated in ore processing. Men typically processed ore in central loca- tions around the village, and women processed ore inside family compounds. The survey included questions about gold ore–processing activities inside and outside the compound, household member and maternal processing activities, history of animal deaths within the compound, and the primary water source of the family. Before data collection, investigators mapped each village and marked the location of each family compound. Global position- ing system (GPS) coordinates were taken at the entrance of each compound to facilitate compound identification and follow-up on blood and environmental testing results. At the end of the investigation, MSF staff visited the compounds and provided parents with blood lead test results of their children as well as information on chelation therapy and the medical management of lead poisoning. Blood sampling. Venous blood was col- lected from children 2 months to 5 years of age. Phlebotomists attempted to draw blood from every available child in village A and from children in every other surveyed com- pound in village B within time constraints. Samples of manufacturer lots of materials used for blood collection were prescreened by CDC laboratories and determined to be free of lead. To prevent sample contamina- tion, all blood collection supplies were kept in plastic gallon-size storage bags before sample collection. In addition, the venipuncture site was thoroughly cleaned with alcohol wipes before the specimen was obtained. One 1- to 3-mL blood sample was collected in a lab- oratory tube and analyzed for lead using a portable blood lead analyzer, LeadCare II® (Magellan Biosciences, Chelmsford, MA, USA) in an uncontaminated area away from the villages. This portable instrument can reli- ably determine BLLs from 3.3 to 65 µg/dL with an accuracy level of ± 3 µg/dL (Freeney A second blood sample was collected from every third child and analyzed for lead, total mercury, and manganese by the Inorganic and Radiation Analytical Toxicology Laboratory at the CDC National Center for Environmental Health in Atlanta, Georgia. Inductively cou- pled plasma mass spectroscopy was used to analyze lead and total mercury. Detailed expla- nations of CDC blood lead and total blood mercury laboratory methods have been pub- lished elsewhere (Caldwell et al. 2009; Jones et al. 2007). Inductively coupled dynamic reaction cell plasma mass spectrometry was used for whole-blood manganese analysis as previously described (Jones et al. 2010). The limit of detection for blood lead is 0.25 µg/dL, total blood mercury 0.33 µg/L, and manganese 0.8 µg/L. Precision was evaluated by moni- toring the replicate results of internal quality control (QC) materials. QC tests, included at the beginning and end of each analytical run, help ensure the accuracy and precision of the analysis process. The low-level QC should be in the low to normal range for blood lev- els in the U.S. population, and the high-level QC should be less than that found in the high-normal population range of the U.S. population. The population ranges are taken from the Fourth National Report on Human Exposure to Environmental Chemicals (CDC 2009). The low-level QC for mercury had an interday coefficient of variation (CV) of 15.1 at 0.516 µg/L and a CV of 2.3 at 5.857 µg/L. For lead, the low-level QC had an interday CV of 1.7 at 2.876 µg/dL and a CV of 1.2 at 12.754 µg/dL. For manganese, the low-level QC, with a mean of 7.983, has a CV of 4.8%, whereas the high-level QC with a mean of 14.929 has a CV of 6.7%. Accuracy for blood lead and mercury was verified by analyzing standard reference material from the National Institute of Standards and Technology The survey collected information about chil- and Zink 2007). ovlume 120 | number 4 | April 2012 • Environmental Health Perspectives