Use of a Novel Ferret System Indicates Increased Air Exchange is Not Effective in Reducing Influenza Transmission in Close Contact Exposure Scenarios

NICOLE C. ROCKEY, Valerie M. Le Sage, Meredith Shephard, Andrea French, Herek L. Clack, Anice Lowen, Aaron Prussin II, Linsey Marr, Seema Lakdawala, University of Pittsburgh

     Abstract Number: 386
     Working Group: Aerosol Science of Infectious Diseases: Lessons and Open Questions on Models, Transmission and Mitigation

Abstract
Airborne transmission of influenza viruses is critical for their epidemiological success. Current experimental systems used to study transmission do not mimic environmental parameters (e.g., air exchange rates, flow patterns) or exposure times in real-world settings. Therefore, results from these traditional systems are likely not representative of the transmission profile in humans. To address this pitfall, we developed a novel transmission setup that better represents a realistic setting and investigated the impact of air exchange rates on transmission events with close contact behaviors, similar to those in childcare settings. In our novel transmission setting, four immunologically naïve recipient ferrets were exposed to a donor ferret infected with 2009 H1N1 pandemic virus (H1N1pdm09) for four hours in a play-based setup. In this novel system, we tested the transmission efficiency of the H1N1pdm09 virus in two different environmental settings: one group with an air exchange rate of ~ 1.3 hr^-1, and the other group with a >10 fold higher air exchange rate of ~ 23 hr^-1. Air and surface samples were collected at various locations within the exposure area for virus quantification. Influenza virus transmission was assessed through viral titration of ferret nasal washes and seroconversion 14 days post-exposure.

Despite over an order of magnitude difference in air exchange rates, transmission efficiency was 50% (i.e., 4 of 8 recipients infected) at both air exchange rates over two independent replicate studies. Presence of infectious virus or viral RNA in surface samples was similar regardless of air exchange rate. However, as expected, more virus-laden aerosols were detected at the lower air exchange rate. Our findings indicate that in close contact, short duration exposures, air exchange rates do not significantly impact transmission efficiency. Interventions such as masking or physical barriers may prove more effective than increased air exchange when close contact is expected to occur.