Inactivation of Aerosolized Viruses in Continuous Air Flow with Axial Heating

Abstract

Thermal inactivation of viruses has been studied in relevance to food sterilization, water purification, and other “non-aerosol” applications, in which heat treatment is applied for a relatively long time. No data are available on the inactivation of airborne viruses exposed to dry heat for a short time, although this is relevant to bio-defense and indoor air quality control. In this study, we investigated inactivation of aerosolized MS2 viruses in a continuous air flow chamber with axial heating resulted from exposures during ∼ 0.1–1 s. For an airborne virion, the characteristic exposure temperature, T _e , was defined utilizing the air temperature profiles in the chamber. The tests were conducted at two air flow rates, Q, which allowed for establishing different thermal flow regimes and exposure time intervals. The experimentally determined inactivation factor, IF, was subjected to correction to account for the temperature profiles. At T _e up to ∼ 90°C (Q = 18 L/min) and up to ∼ 140°C (Q = 36 L/min), the loss of viral infectivity was relatively modest (≤ 10). However, IF increased exponentially as T _e rose from ∼ 90°C to ∼ 160°C (for 18 L/min) or from ∼ 140°C to ∼ 230°C (for 36 L/min). Under specific thermal exposure conditions (∼ 170°C and ∼ 250°C, respectively), IF exceeded ∼ 2.4 × 10⁴ (∼ 99.996% infectivity loss)—the maximum quantifiable in this study. The airborne MS2 virions exposed to hot air for < 1 s were found to have survived much higher temperatures than those subjected to thermal treatment in liquid for minutes or hours. The findings are significant for establishing limitations of the heat-based bioaerosol control methods.

The authors gratefully acknowledge the support from the Defense Threat Reduction Agency (US Department of Defense) through grant HDTRA-1-08-1-0012. The authors are also thankful to Dr. S. Mohan for assisting in the temperature analysis.

Chunlei Li is on leave from Fudan University, Shanghai, People's Republic of China.

Notes

¹ It is common in microbiology to use the “log inactivation” by quantifying log ₁₀(IF).

² Straight lines in Figure 3 are drawn through the data points and do not aim at representing specific linear trends.