[1] Statens Serum Inst, Dept Clin Biochem, DK-2300 Copenhagen, Denmark
[2] Univ Aarhus, Inst Publ Hlth, Dept Epidemiol, NANEA, Aarhus, Denmark
[3] Univ So Denmark, Dept Biochem & Mol Biol, Odense, Denmark
[4] Univ Bristol, Dept Pathol & Microbiol, Bristol, Avon, England