Evidence of spatial clustering of childhood acute lymphoblastic leukemia cases in Greater Mexico City: report from the Mexican Inter-Institutional Group for the identification of the causes of childhood leukemia.

Background: A heterogeneous geographic distribution of childhood acute lymphoblastic leukemia (ALL) cases has been described, possibly, related to the presence of different environmental factors. The aim of the present study was to explore the geographical distribution of childhood ALL cases in Greater Mexico City (GMC). Methods: A population-based case-control study was conducted. Children <18 years old, newly diagnosed with ALL and residents of GMC were included. Controls were patients without leukemia recruited from second-level public hospitals, frequency-matched by sex, age, and health institution with the cases. The residence address where the patients lived during the last year before diagnosis (cases) or the interview (controls) was used for geolocation. Kulldorff's spatial scan statistic was used to detect spatial clusters (SCs). Relative risks (RR), associated p-value and number of cases included for each cluster were obtained. Results: A total of 1054 cases with ALL were analyzed. Of these, 408 (38.7%) were distributed across eight SCs detected. A relative risk of 1.61 (p<0.0001) was observed for the main cluster. Similar results were noted for the remaining seven ones. Additionally, a proximity between SCs, electrical installations and petrochemical facilities was observed. Conclusions: The identification of SCs in certain regions of GMC suggest the possible role of environmental factors in the etiology of childhood ALL.

Geographical distribution of optic nerve hypoplasia and septo-optic dysplasia in Northwest England.

OBJECTIVE: To study the distribution of septo-optic dysplasia (SOD) and optic nerve hypoplasia (ONH) in the Greater Manchester and Lancashire (GM&L) region of Northwest England, and to analyze occurrence by location and over time. STUDY DESIGN: A population-based incidence study was undertaken for cases of SOD/ONH from GM&L. Standardized incidence ratio (SIR) for each district, relationships between SIRs and possible geographically varying risk factors, and spatial and space-time clustering were analyzed. RESULTS: Eighty-seven cases had a confirmed diagnosis of ONH/SOD giving an incidence of 10.9/100,000 per year in GM&L. SIRs ranged widely but were significantly elevated (lower confidence limit >100) in three districts: 167%, 192%, and 198%, respectively. All three were high population density, inner-city locations. SIRs were significantly correlated with higher rates of unemployment (r = 0.49, P = .01), dependent children in non-earning households (r = 0.47, P = .02), underage conceptions (r = 0.46, P = .02), and underage pregnancies (r = 0.44, P = .03). There was no evidence of spatial or space-time clustering. CONCLUSIONS: The incidence of ONH/SOD in GM&L was higher than that reported elsewhere. Cases were more common in areas that had higher unemployment and teenage pregnancy rates.