  In a recent paper [S.El Boustani, P.R.Buenzli, and Ph.A.Martin, Phys.Rev. E
73, 036113 (2006) cond-mat/0511537], about quantum charges in equilibrium with
radiation, among other things the asymptotic form of the electric-field
correlation has been obtained by a microscopic calculation. It has been found
that this correlation has a long-range algebraic decay (except in the classical
limit). The macroscopic approach, in the Course of Theoretical Physics of
Landau and Lifshitz, gives no such long-range algebraic decay. In this Brief
Report, we revisit and complete the macroscopic approach of Landau and
Lifshitz, we confirm their result, and suggest that, perhaps, the use of a
classical electromagnetic field by El Boustani et al. was not justified.
