The Relative Stability of Influenza Virus Infectious Unit and Gene Copy Measurements on Surfaces

KE ZHANG, Will Fitzsimmons, Adam Lauring, Krista Wigginton, University of Michigan

     Abstract Number: 771
     Working Group: Health-Related Aerosols

Abstract
Influenza viruses are among the most common and most significant causes of human respiratory infections by posing a considerable threat to public health each year. The transmission of influenza viruses depends on infectious virus particles (i.e., infectious units, iu), however environmental measurements often quantify the genome copy (gc) concentrations by PCR-based assays (i.e., gene copies, gc). The ratios of gene copies to infectious units likely change through the release, aging, and collection of viruses from the environment. We quantified both infectious unit and genome copy concentrations for influenza viruses and surrogate viruses (i.e., MS2, and phi6) as they aged on environmental surfaces to help aid in the interpretation of risks from gene copy measurements. We found the gc concentration of RNA viruses are often vastly underestimated due to reverse transcription (RT) efficiencies of less than 100% and therefore optimized our assays to improve RT efficiencies and adjusted the absolute gene copy concentrations to account for RT efficiencies. We observed that the virus gc concentrations were relatively stable on environmental surfaces over several days. Infectious influenza virus concentrations, however, dramatically decreased over the experimental periods, leading to increased gc/iu ratios. Furthermore, we found the changes in gc/iu ratios were affected by environmental conditions (e.g., relative humidity). Our results contribute to the accurate and robust environmental surveillance of influenza viruses, which will improve the transmission models and the assessment of intervention effectiveness.