Fumigation in a CLIII room using a Laycock Fumigator (Tolbest Ltd). doi:10.1371/journal.pone.0027932.t001 immunocompetent patient who was hospitalised briefly at the start of their illness, but recovered. This virus does not form discrete plaques in MDCK cells and could therefore not be titred by this method. Instead, virus stocks were quantified by qPCR for segment 7 [12] . Although this method scores viable and non-viable virus particles alike, preparations of wild type influenza A viruses generally have similar particle:PFU ratios and quantitative comparison of RT-PCR and other titration methods have shown good agreement [13, 14] . The AH04 stock contained 6.5610 8 genome copies/ml and was used at a 1:10 dilution as for PR8. For comparison, the PR8 stock had a genome titre of 1.6610 11 genome copies/ml.