Childhood lead poisoning in Zamfara State, Nigeria eight symptomatic children revealed BLLs of 168–370 µg/dL, levels known to be fatal in children. The unprecedented level of morbid- ity and mortality raised suspicion about other concomitant diseases such as malaria and bacterial infections; however, laboratory tests failed to demonstrate microorganisms in most patients, and the illnesses did not respond to antimalarials and empiric antibiotics. During May 2010, the Nigerian Federal Ministry of Health assembled a multidisciplinary team consisting of representatives from the Nigerian Field Epidemiology and Laboratory Training Program (NFELTP), Zamfara State Ministry of Health, the CDC, and the World Health Organization (WHO) to join MSF in investigating the outbreak (CDC 2010). During May–June 2010, the team sur- veyed the two most-affected villages and confirmed lead poisoning as the cause of the outbreak (CDC 2010; Dooyema et al. 2012). Among these two villages, 25% of children < 5 years of age had died during the previ- ous 12 months, and 82% of these had expe- rienced convulsions before death. All of the 204 children < 5 years of age who were tested had BLLs ≥ 10 µg/dL, and 97% had BLLs ≥ 45 µg/dL. Lead-rich gold ore was identified in both villages. Gold ore–processing activi- ties had begun during the previous 12 months inside a majority of family compounds. Two- thirds of households reported processing gold ore inside family compounds, and soil-lead levels in 85% of family compounds exceeded the U.S. Environmental Protection Agency (EPA) soil-lead standard [400 parts per million (ppm)] for areas of bare soil where children play (U.S. EPA 2003). Factors associated with child mortality in the two surveyed villages were the child’s age, maternal participation in ore processing, and environmental factors such as primary water source type and soil-lead level of the family compound (Dooyema et al. 2012). The investigation concluded that 118 child fatalities were strongly associated with gold ore processing. During June 2010, the Nigerian Federal Ministry of Health granted expedited approval for therapeutic use of the oral chelating agent meso-2,3-dimercaptosuccinic acid in Nigeria. In response to this public health emergency, the federal government of Nigeria, the Zamfara State government, and international stake- holders including the WHO, the United Nations International Children’s Fund, MSF, TerraGraphics Environmental Engineering, Inc., and CDC jointly implemented control measures, including provision of oral chelation therapy, remediation of lead-contaminated fam- ily compounds, public health messaging about lead poisoning, and social mobilization activi- ties to advise villagers to move gold ore pro- cessing out of family compounds and villages. Efforts of stakeholders during June–September 2010 resulted in identification of childhood lead poisoning in five additional villages in Zamfara State. By September 2010, > 350 cases of childhood lead poisoning were confirmed. However, local public health professionals in Zamfara State continued to identify addi- tional villages with childhood convulsions and deaths that were suspicious for lead poisoning but not laboratory confirmed. At that time, stakeholders were unable to quantify the num- ber of affected villages. Therefore, the Nigerian Federal Ministry of Health requested that the CDC conduct a follow-up investigation. In contrast to the door-to-door survey among two affected villages conducted during May–June 2010 (Dooyema et al. 2012), this investigation was designed as a rapid assessment to investigate the geographic extent of childhood lead poi- soning and lead contamination among villages in Zamfara State and to identify villages that should be prioritized for lead hazard abatement and other urgent interventions. Methods Setting and sampling of villages. Zamfara State has 14 local government areas (LGAs). Each LGA, with an area ranging from 674 to 6,654 km2, contains multiple villages within its jurisdiction. A village typically consists of earthen-walled compounds containing open- air dwellings with bare compacted soil floors. Each compound houses at least 1 family. Each village has a chief who interacts with the cor- responding local government and traditional leadership system. Census and vital statistics data were unavailable at the village level. We used chain-referral sampling to identify villages of interest, defined as vil- lages suspected of participation in any gold ore–processing activity during the previous 12 months (October 2009–October 2010) in Zamfara State (Salganik and Heckathorn, 2004). We used chain-referral sampling rather than random sampling to facilitate rapid iden- tification of potentially affected villages. Our chain-referral sampling technique involved an iterative, cyclical process to identify vil- lages of interest. After advocacy visits to state government officials, we visited traditional leaders, local government officials, and stake- holders in the response efforts, asked them to provide a list of villages in their jurisdic- tion that likely participated in gold ore pro- cessing, and developed an aggregate village list. During village visits, we asked villagers to list other villages in their area that likely par- ticipated in gold ore processing, added these names to the aggregate list, and repeated the process in subsequent villages. The cycle was repeated during the 5-week operation period (15 October–18 November 2010) to compile a comprehensive list of villages of interest. Interviews. Field investigations were con- ducted by members from the CDC, NFELTP, Environmental Health Perspectives • volume 120 | number 10 | October 2012 and Zamfara State Ministry of Health. Each field team consisted of three to five members and was assigned particular villages of inter- est. Local traditional leaders designated one to two representatives to accompany and intro- duce the team to each village. Teams asked the village chief to hold an informal village- wide meeting, informed assembled villagers (predominantly male adults because of cul- tural norms) of the purpose of the visit, and administered the questionnaire in the local language by interviewing villagers collectively, including the village chief. We used a village- wide meeting instead of only interviewing the village chief because the chief might not know all of the answers or might be reluctant to dis- close gold ore–processing activities for fear of legal or economic consequences. The meeting allowed all participating villagers to contrib- ute answers. If villagers disagreed about an answer, the interviewer asked for a consensus decision and recorded the final answer agreed to. Responses were entered into an Epi-Info software version 3.5.1 (CDC, Atlanta, GA, USA) electronic database. This investigation was conducted in accordance with the Declaration of Helsinki, developed by the World Medical Association (World Medical Association 2008). The Human Subjects Review Board at the CDC determined that this investigation was a pub- lic health response that was exempt from full institutional review board review. Questionnaire instrument. We developed a questionnaire to collect information at the village level on the following: estimated num- ber of people and compounds; presence and estimated number of children < 5 years of age who had a history of convulsions during the previous 12 months; presence and estimated number of children < 5 years of age who had a history of convulsions and had died dur- ing the previous 12 months; presence and types of gold ore–processing activities during the previous 12 months; and other villages likely to have participated in gold ore process- ing. Gold ore processing consists of a limited number of core activities [e.g., breaking rock, grinding, washing, drying, amalgamation (using mercury), and melting]. Definitions of these activities have been described previously (Dooyema et al. 2012). Villages might not have participated in all of the ore-processing activities. Villages that reported any gold ore–processing activity were asked to indicate where the ore had been mined. Blood collection and analysis. Because our objective was to rapidly identify and prioritize villages with childhood lead poisoning for interventions, we used the following hierarchy to select approximately five children 2 months to 5 years of age in each village of interest for blood collection: First, we asked to col- lect blood samples from children who lived 1451