A cluster of three cases of aplastic anaemia in children.

During a 2-week period three unrelated children presented with severe aplastic anaemia at a general hospital serving a population of 25,000 children aged 0-15 years. The probability of this occurring by chance alone was 0.00009 (exact probability cluster analysis). Serology for common viral infections including hepatitis A & B and infectious mononucleosis was negative. It was not possible to demonstrate IgM antibodies to human parvovirus (HPV) by radioimmunoprecipitation or HPV virions by DNA hybridization in the patients or any members of their families. Epidemiological investigation failed to demonstrate a common environmental toxin. It did reveal, however, that all three patients had spent time, within the preceding 3 months in a swimming pool and its surrounding area in a region of Cardiff where none of them resided. Pool maintenance was satisfactory and water analysis showed no abnormality. The possibility must remain that the cluster was caused by an undisclosed environmental toxin.