Survival of the Enveloped Virus Phi6 in Droplets as a Function of Relative Humidity, Absolute Humidity, and Temperature

Abstract

Infectious diseases caused by enveloped viruses, such as influenza, severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS), cause thousands of deaths and billions of dollars of economic losses per year. Studies have found a relationship among temperature, humidity, and influenza virus incidence, transmission, or survival; however, there are contradictory claims about whether absolute humidity (AH) or relative humidity (RH) is most important in mediating virus infectivity. Using the enveloped bacteriophage Phi6, which has been suggested as a surrogate for influenza viruses and coronaviruses, we designed a study to discern whether AH, RH, or temperature is a better predictor of virus survival in droplets. Our results show that Phi6 survived best at high (>85%) and low (<60%) RHs, with a significant decrease in infectivity at mid-range RHs (∼60 to 85%). At an AH of less than 22 g · m−3, the loss in infectivity was less than 2 orders of magnitude; however, when the AH was greater than 22 g · m−3, the loss in infectivity was typically greater than 6 orders of magnitude. At a fixed RH of 75%, infectivity was very sensitive to temperature, decreasing two orders of magnitude between 19°C and 25°C. We used random forest modeling to identify the best environmental predictors for modulating virus infectivity. The model explained 83% of variation in Phi6 infectivity and suggested that RH is the most important factor in controlling virus infectivity in droplets. This research provides novel information about the complex interplay between temperature, humidity, and the survival of viruses in droplets.IMPORTANCE Enveloped viruses are responsible for a number of infectious diseases resulting in thousands of deaths and billions of dollars of economic losses per year in the United States. There has been a lively debate in the literature over whether absolute humidity (AH) or relative humidity (RH) modulates virus infectivity. We designed a controlled study and used advanced statistical modeling techniques specifically to address this question. By providing an improved understanding of the relationship between environmental conditions and virus infectivity, our work will ultimately lead to improved strategies for predicting and controlling disease transmission.

Role of temperature and humidity in the modulation of the doubling time of COVID-19 cases

“…These results are in agreement with other studies that suggested that the aerosol spread of the influenza virus is both dependent upon relative humidity and temperature, although performed in animal models 14 , and that the virus survival in droplets is higher at high humidity levels with a significant decrease on its infectivity rate at mid-levels of humidity 15 . Additionally, other authors suggest that some diseases spread faster in high humidity levels 16 , reporting an odds ratio for a community-acquired pneumonia case, diagnosed with leggionaire's disease a , 3.1 times higher in high humidity level (above 80%) than when submitted to humidity levels below 50%, at temperatures of 16-27 ºC (60º-80ºF).…”

Climate factors and incidence of Middle East respiratory syndrome coronavirus

“…3. This is similar to previous reports where MERS-CoV cases increased with low humidity [9,[11][12][13]. Our findings may clarify viral seasonality, as it explains why most MERS-CoV outbreaks occurred between April and August, where temperatures reached the highest and humidity reached the lowest [14].…”

“…The strength of this study is the large number of MERS-CoV patients included in the analysis, and the study identifies important factors affecting MERS-CoV viral seasonality. In agreement with previous reports [11,13], the study highlights the need for considering climate factors on MERS-CoV guidelines for control measures and prevention. The overall findings of the study are that the higher the temperature and ultraviolet index, the higher incidence of MERS-CoV infections, and vice versa for humidity and wind speed.…”

Evaluation of bioaerosol samplers for the detection and quantification of influenza virus from artificial aerosols and influenza virus–infected ferrets

“…Utilizing an established guinea pig model of transmission, Lowen et al demonstrated that low RH (20%‐30%) is optimal for influenza virus transmission . Prussin et al also demonstrated the same influence of low RH on infectivity using bacteriophages . Testing bioaerosol samplers under a range of IAV transmission conditions is essential for determining the usefulness of these sampling devices.…”