Inactivation of Airborne Influenza Virus Using Low Concentration of Chlorine Dioxide: About the Relative Humidity-dependency
Hidekazu NISHIMURA1), Hiroyuki HAYASHI2), Shigeru URA2) and Soichiro SAKATA3)
1)Virus Research Center, Clinical Research Division, Sendai Medical Center, National Hospital Organization, Sendai, Japan2)Research & Development Division, AMTEC Co., Ltd., Osaka, Japan3)Takasago Thermal Engineering Co., Ltd., Tokyo, Japan
Chlorine dioxide gas has bactericidal and virucidal abilities. However, it is unstable under high humidity, and it is difficult to keep its concentration low in a high-humidity, closed environment. We have now developed a methodology that can maintain low chlorine dioxide concentration in air even under high humidity. Using this method, the effect of humidity on airborne influenza virus inactivation by exposing the virus to the gas at a very low concentration was examined: the gas concentration was set between 20-30 ppb, which is considered to be the maximum limit concentration that people can tolerate in a day; room temperature at 21.5°C; relative humidity (RH) at 30%, 50% or 70%. For each condition, the virus was atomized in the closed chamber, and after 20 minutes, the virus in the air was collected for titration. The result showed only a slight and statistically insignificant decrease of virus titer in the air collected from 30% RH environment, compared with that of non-gas exposed control. On the other hand, statistically significant decrease of virus titer was observed under 50% and 70% RH; a reduction of about 0.3% and 0.03%, respectively, from the initial airborne influenza virus load, while the reduction in the non-gas control was about 10% and 1%, respectively, and it was statistically significant.Thus, it was shown that chlorine dioxide at low concentration of less than 20-30 ppb has an ability to inactivate airborne influenza virus under 50% and 70% RH conditions. However, from a viewpoint of infection control, it is a minor effect for reducing infection risk, which is merely additional to the major effect by the humidity itself of 50% and 70% RH conditions, when we consider the actual load of viruses released from an influenza patient in a room space and still remain active after certain time. Besides, it was also observed that such a low concentration of chlorine dioxide is almost meaningless for the infection control under 30% RH condition which is commonly observed as normal humidity in the temperate zones in winter.
Key words：chlorine dioxide, influenza virus, humidity, air-borne, inactivation
Received: March 10, 2017
Accepted: June 22, 2017