When PR8 surface viability was assessed by plaque assay, virus inoculated onto a control surface of a tissue culture dish could be recovered efficiently at t0, but thereafter infectivity fell away rapidly with no live virus recovered at 24 h (Table 4 ). Fitting the data to a one-phase exponential decay model (Fig. 1B ) estimated the t 1/2 of the virus under these conditions to be around 1.5 h. A similar pattern of rapid loss of infectivity was seen when the household surface samples were tested, with the difference that greater initial losses of infectivity ranging between 20-fold (telephone handset) to nearly 4000-fold (unsealed pine) were seen (Table 4 ). Nevertheless, viable virus was recovered at 4 h (but not later) from the silver-impregnated cloth, soft toy fabric and in trace quantities, from light switch material. The only material (other than the control tissue culture dish) for which even low amounts of viable virus could be detected at 9 h was stainless steel. Thus despite the persistence of the viral genome on a wide variety of household surfaces, PR8 infectivity decayed sharply, with evidence of significant contact effects from some materials; most notably unsealed pine, but also a wide variety of other porous and nonporous surfaces.