Long-term observational study on 6223 survivors of arsenic poisoning due to contaminated milk powder during infancy.

In 1955, an outbreak of arsenic poisoning caused by the ingestion of arsenic-contaminated Morinaga Dry Milk occurred in western Japan. This study aimed to assess the mortality and cancer incidence risk among Japanese individuals who were poisoned during this time as infants. In total, 6223 survivors (mean age at enrollment, 27.5 y) who had ingested contaminated milk when they were aged ≤ 2 y participated in this study. Follow-up was conducted from 1982 to 2018 (mean follow-up duration, 30.3 y). Standardized mortality ratio (SMR) and standardized incidence ratio (SIR) were used to compare mortality and cancer incidence rates of subjects with the respective Japanese population rates, and 95% confidence intervals (95% CIs) of the SMR and SIR were also calculated. In total, 561 deaths and 524 new cancer cases were observed. A statistically significant increase in mortality rate was observed for all causes (SMR, 1.15; 1.01-1.19), nervous system disease (2.83, 1.62-4.19), respiratory disease (2.02, 1.37-2.62), genitourinary system disease (2.25, 1.10-3.73), and traffic accident (2.03, 1.14-3.04). In contrast, a significant decrease in cancer incidence rate was observed for all cancers (SIR, 0.96; 0.84-0.99), stomach cancer (0.77, 0.57-0.92), colon cancer (0.63, 0.41-0.85), rectum cancer (0.69, 0.43-0.95), and breast cancer (0.72, 0.52-0.89). Liver cancer showed a high mortality rate (SMR, 1.68; 1.06-2.31). In this study, after the long-term follow-up we revealed overall and cause-specific mortality and cancer incidence risk among survivors who ingested arsenic-contaminated dry milk as infants.