Abstract: The present invention refers to a method for isolating a nucleic acid, said method comprising: a) provision of a fluid test sample, which comprises i) a biological sample, ii) a chaotropic agent with a concentration of at least 1 M in the fluid test sample, and iii) a detergent, b) contacting said fluid test sample with a medium for size-exclusion chromatography, and c) purifying the nucleic acid with size- exclusion chromatography. The present invention further relates to the use of any of the methods according to the present invention for detecting a viral infection as well as to a method for detecting a viral infection. The present invention further relates to a kit-of-parts comprising a medium for size- exclusion and a size-exclusion chromatography device for isolating the nucleic acid of the fluid test sample.