There was a false detection of virus in 3 samples, but they were all within the same family as previously tested for in the routine analysis, JCV in a BKV + urine sample, Rota C in a Rota A + faeces sample and Dengue 2 in a Dengue 1 + serum sample. They could all be explained by cross-reactivity between the probes targeting one species with other species in the same viral family. Future improvements to the current probe design can address crossreactivity issues such as these described. Regarding the failure to detect Sapovirus in the double-positive Astrovirus + /Sapovirus + faeces sample, we believe the reason was poor amplification due to low viral copy number rather than a specificity problem, since Sapovirus was detected in the Sapovirus + faeces sample ( Table 2) . Supporting this is the Sapovirus-specific PCR used before and after Phi29-amplification (Table 1) , which indicates that the singlepositive sample had more amplified Sapovirus (Ct = 11) after amplification, compared to the double-positive sample (Ct = 18) and thereby a sufficient amount for a successful detection by microarray analysis.