[1] Statens Serum Inst, Microbiol Diagnost & Virol, DK-2300 Copenhagen, Denmark
[2] Statens Serum Inst, Dept Epidemiol Res, DK-2300 Copenhagen, Denmark
[3] Statens Serum Inst, Neisseria & Streptococcus Reference Lab, DK-2300 Copenhagen, Denmark
[4] Statens Serum Inst, Dept Infect Dis Epidemiol, DK-2300 Copenhagen, Denmark
[5] Univ Copenhagen, Hvidovre Hosp, Dept Gastroenterol, DK-2650 Hvidovre, Denmark