Summary of the contaminant content of nasopharyngeal samples from Thailand. a) The PCoA plot appears to show age-related clustering; however, b) extraction kit lot explains the pattern better. c) When coloured by age, the plot shows the loss of the initial clustering pattern after excluding contaminant OTUs from ordination. d) The proportion of reads attributed to contaminant OTUs for each sample, demonstrating that the first two kits were the most heavily contaminated. e) Genus-level profile of contaminant OTUs for each kit used.