- Correspondence to Dr Morten Frisch, Department of Epidemiology Research, Statens Serum Institut, 5 Artillerivej, DK-2300 Copenhagen S, Denmark;
- Revised 20 August 2010
- Accepted 23 August 2010
- Published in print 1 March 2011.
- Published online 4 February 2011.
- Published first 29 December 2010.
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