3. Results
Ten microlitre of 107 TCID50 per mL of virus was placed in individual wells of a 24-well plastic plate (representing a nonporous surface) and dried. The dried virus was then incubated at different temperatures (38°C, 33°C, 28°C) at different relative humidity (>95%, 80~89%) for 3 hr, 7 hr, 11 hr, 13 hr, and 24 hr and the residual viral infectivity was titrated. A similar experiment was conducted at room temperature and relative humidity of about 40–50% (air-conditioned room) for up to 4 weeks. Virus dried on plastic retained viability for up to 5 days at 22~25°C at relative humidity of 40~50% with only 1 log⁡10 loss of titre (Figure 1). After that virus infectivity is gradually lost ever time. Loss of virus infectivity in solution was generally similar to dried virus under these environmental conditions. This indicates that SARS CoV is a stable virus that may potentially be transmitted by indirect contact or fomites, especially in air-conditioned environments.  
High relative humidity (>95%) at comparatively low temperature (28°C and 33°C) did not affect the virus infectivity significantly (Figure 2(a)). High temperature (38°C) at 80–90% relative humidity led to a 0.25~2  log⁡10 loss of titre at 24 hr (Figure 2(b)). However, if the dried virus was stored at high temperature (38°C) and high relative humidity (>95%), there was a further ~1.5 log⁡ loss of titre for each time point up to 24 hr (0.38~3.38 log⁡10) when compared with high temperature (38°C) at a lower relative humidity 80–90% (Figures 3(a)–3(c)).