Human airway epithelial cell culture model of MERS infection and the kinetics of the host response. A. Calu-3 2B4 cells were infected with either MERS-CoV SA 1 or MERS-CoV Eng 1 (MOI 5). Cell lysates were harvested at 3, 7, 12, 18 and 24 hpi and viral genomic RNA measured by qRT-PCR using forward primer (KL200F) and reverse primer (KL201) spanning the CoV genome (Additional file 1: Table S5). The error bars represent the standard deviation among triplicate samples. B. Clustering graph for samples according to their Euclidean distances in gene expression obtained by an integration of viral genomic RNA levels. Samples with similar viral genomic RNA levels were grouped together. Using statistical criteria on the single linkage heights between all samples, we extracted the highly interconnected part (with smaller linkage heights). These samples were compared to highly interconnected samples of a second group of samples with overlapping viral genomic RNA levels of the first group and so forth. Whenever two highly interconnected parts had at least one sample in common we defined the two groups as adjacent. In the clustering graph, adjacent sample groups are linked by an edge, the node color represents the average viral genomic RNA levels of each sample group. Edge length or distance between nodes in the graph does not recapitulate spatial closeness of samples.