The international follow-up of individuals potentially exposed to polonium-210 in London 2006

Objectives: Following a death from polonium-210 (²¹⁰Po), contamination was found at several sites in London. This paper describes the UK Health Protection Agency's follow-up and assessment of individuals resident overseas who were potentially exposed to ²¹⁰Po. Study design: Descriptive follow-up study. Methods: Individuals were classified into three exposure groups (higher, lower and unknown). Presence and degree of internal contamination were measured by 24-h urinary ²¹⁰Po activity (mBq/day). Results over 30mBq/day were taken to indicate probable contact with ²¹⁰Po in this incident. Dose assessments were conducted to determine degree of exposure and to identify individuals requiring further follow-up. Results: Overall, 664 potentially exposed persons from 52 countries and territories were identified. Of these, 157 (24%) were in the higher exposure category, and urinary measurements were reported for 31% (48/157). Results for 19% (9/48) of those at higher exposure were more than 30. mBq/day. For those at lower exposure, the percentage was 4% (3/68). Results above 30. mBq/day were significantly more likely to be reported for the higher exposure category than the lower exposure category (Fisher's exact test P=0.010). Reported dose assessments suggested that identified individuals were not at increased health risk in the long term. Challenges and practical lessons were identified during the investigation. Conclusion: The results suggest that it is unlikely that any overseas resident had significant internal contamination with ²¹⁰Po. However, this incident clearly demonstrated the scale of international involvement likely to be necessary in other public health emergencies in large cities. The lessons identified have implications for the international health community, particularly with regard to the follow-up of individuals exposed to radiation in one country who then travel to another.