Spread of acute hemorrhagic conjunctivitis due to enterovirus-70: effect of air temperature and relative humidity on virus survival on fomites

Enterovirus 70 (EV-70) has caused at least two pandemics and several major epidemics of acute hemorrhagic conjunctivitis (AHC) in the past 18 years, with the largest number of cases occurring in the coastal areas of the tropics. The exact means of its spread are not known, but fomites and hands contaminated by them are the most likely vehicles. We, therefore, tested EV-70 survival under different environmental conditions using stainless steel disks (1 cm diameter). Each disk received 10 microliter of the virus in phosphate-buffered saline (PBS). The disks were held at various temperatures with the relative humidity (RH) at the low (20 +/- 5%), medium (50 +/- 5%), high (80 +/- 5%), or ultrahigh (95 +/- 5%) level. The virus was eluted from the disks with tryptose phosphate broth and the eluate assayed in LLC-MK2cells. Inactivation rates (Ki), expressed as hourly loss of virus plaque forming units (PFU) in log10, were then calculated. At 20 degrees C, virus survival was proportional to the RH level, with the highest virus survival at the ultrahigh RH; at this level nearly 5% of the input virus was detectable even after 24 hr. Virus inactivation rates were only slightly higher at the ultrahigh RH when the temperature was raised to 33 degrees C or 35 degrees C. However, at 80% RH, increasing the temperature from 20 degrees C to 33 degrees C resulted in a dramatic rise in virus inactivation. The finding that high levels of RH prolong EV-70 survival on fomites may help explain the epidemiology of AHC resulting from EV-70.