Infectious Disease Transmission in Airliner Cabins *Qingyan “Yan” Chen, Ph.D.; James J. McDevitt, Ph.D., CIH; Jitendra K. Gupta, Ph.D.; Byron W. Jones, P.E., Ph.D.; Sagnik Mazumdar, Ph.D.; Stephane B. Poussou, Ph.D.; and John D. Spengler, Ph.D. National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) Airliner Cabin Environment Research Program Harvard School of Public Health; Kansas State University; and Purdue University February 22, 2012 Report No. RITE-ACER-CoE-2012-01 *Authors’ names appear alphabetically. NOTICE ___________ This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The United States Government assumes no liability for the contents thereof. ___________ This work was funded by the U.S Federal Aviation Administration Office of Aerospace Medicine under Cooperative Agreements 07-C-RITE and 10-C-RITE. ___________ This publication is available in full-text from the publications Web site of the National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) at: www.acer-coe.org Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. RITE-ACER-CoE-2012-01 4. Title and Subtitle 5. Report Date Infectious Disease Transmission in Airliner Cabins February 22, 2012 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Qingyan “Yan” Chen, James J. McDevitt, Jitendra K. Gupta, Byron W. Jones, Sagnik Mazumdar, Stephane B. Poussou, and John D. Spengler 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Harvard School of Public Heath Boston, Massachusetts 11. Contract or Grant No. Kansas State University Manhattan, Kansa Purdue University West Lafayette, Indiana 07-C-RITE and 10-C-RITE 12. Sponsoring Agency name and Address 13. Type of Report and Period Covered Office of Aerospace Medicine Technical Report 2/1/2009 to 12/31/2011 Federal Aviation Administration 800 Independence Ave., S.W. Washington, DC 20591 14. Sponsoring Agency Code 15. Supplemental Notes Work was accomplished under Public law 108-76. 16. Abstract Airborne disease transmission has always been a topic of wide interest in various fields for decades. This report shows the study of the entire disease transmission route in an airliner cabin from the infectious agents generated by an index patient to the fellow passengers and crew members. The investigation developed exhalation/inhalation models for coughing, breathing and talking with human subjects. The transport of these expiratory droplets in an aircraft was investigated using the CFD methods. It was found that the bulk airflow pattern in the cabin played the most important role on the droplet transport. The deterministic and probabilistic approaches (Wells Riley equation) can be used to quantify the risk of infection based on the inhaled infectious dose. By assuming an index passenger with influenza the deterministic approach can calculate the amount of influenza virus ribonucleic acid (RNA) particle inhaled by each passenger and the probabilistic approach can determine the risk of infection for each passenger. Further experimental and CFD investigations revealed that in-flight movement of passengers and crew members had a significant impact on infectious disease transmission inside airliner cabins. The investigation showed that the movement of a passenger/crew member could be the reason behind the transmission of SARS viruses to passengers seated as far as seven rows from the infected passenger during the SARS outbreak in 2003. An important route for disease transmission is by deposition of droplets or particles on surfaces followed by contact with the surfaces. Experimental methods to measure particle deposition in a full-scale cabin mockup were developed. This investigation has also developed a better understanding of surface contamination in the air cabin through laboratory investigation and a pilot field study. The laboratory investigation focused on evaluating survival of influenza virus on surfaces and developing a field, microbial, surface sampling protocol for use in the air cabin environment. The results of our investigation show that influenza survival on stainless steel surfaces are impacted by relative humidity. 17. Key Words 18. Distribution Statement Virus, influenza, SARS, models, experiment, risk, airflow, relative humidity, particles, deposition, movement, in-flight 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 172 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized A-1 EXECTIVE SUMMARY Airborne disease transmission has always been a topic of wide interest in various fields for decades. The transmission of bacterial and viral pathogens from inanimate surfaces to susceptible persons is a concern with regard to infectious disease transmission. For infection to occur, the pathogenic organisms must be present and survive on the environmental surface until such a time that the pathogen is transferred to a susceptible host at the appropriate route of entry. The air cabin is a unique environment for disease transmission. The air cabin has a high occupation density with a high passenger through-put. While seated for hours at a time, “sick” individuals have ample opportunity to contaminate their surrounding area. Once surfaces in the air cabin become contaminated, susceptible persons in the immediate area may come into contact with the contaminated surfaces. The transmission of airborne disease starts when the infectious agents such as the influenza virus or Mycobacterium tuberculosis are exhaled from an infected person. The infectious agents are then dispersed and finally inhaled by a susceptible person. The transmission of infectious diseases in indoor environments, especially in aircraft cabins may represent great risk as they have high occupant density and need to be investigated. With the recent advancements, Computational Fluid Dynamics (CFD) has become a powerful tool for predicting the transmission of airborne diseases in indoor environments. The CFD simulations need precise thermo-fluid boundary conditions for the exhalation/inhalation during various respiratory events and reliable flow models to accurately predict the transport of the infectious agents. The present study first developed exhalation/inhalation models for coughing, breathing and talking. The study conducted measurements on the exhaled/inhaled flow rate, flow direction and area of mouth/nose opening with human subjects. The flow rate variation over time can be defined as a combination of gamma functions for a cough; sinusoidal function for breathing, and a constant for talking process. The variables required to define these flow rate functions can be obtained from the physiological details of a person. The direction of the exhalation jet and the area of mouth/nose opening did not vary significantly during these processes. Though variation among people existed but had no correlation with the physiological details of a person. Thus a mean value for these parameters can be used as boundary condition. In summary, a set of mathematical equations were developed to provide the flow boundary conditions to the CFD simulations for the coughing, breathing and talking processes. The equations account for the variation in the flow boundary conditions with time and people. The droplets exhaled by an infectious person are the carriers of infectious agents. The transport of these expiratory droplets in an aircraft was investigated using the CFD methods. The developed exhalation/inhalation boundary conditions were used. A seven- row, twin-aisle, fully-occupied cabin with index passenger seated at the center was investigated. The droplets exhaled were from a single cough, a single breath and a 15-s talk of the index passenger. The droplets were tracked by using Lagrangian method and their evaporation was modeled. It was found that the bulk airflow pattern in the cabin played the most important role on the droplet transport. The droplets were contained in the row before, at, and after the index patient within 30 s and dispersed uniformly to all the seven rows in 4 minutes. For the cough case, the total airborne droplet fraction ‐ 1 ‐ reduced to 48%, 32%, 20%, and 12% after 1, 2, 3 and 4 minutes respectively. Similar observations were made for the breathing and talking cases. The study further developed methods to predict the spatial and temporal distribution of expiratory droplets for any flight duration based on the 4 minutes of CFD simulations. The CFD simulations indicated that the local droplet concentrations were higher in the zone, where the expiratory droplets first reached. The droplets concentration then reduced due to the constant dispersion and removal of the droplets from the outlets. The variation in the droplet concentration in the vicinity of the passengers with time indicated that the droplets got well mixed in the cabin in 3 minutes, thus perfectly mixed conditions can be assumed beyond 3 minutes. The droplets from multiple exhalations from the index passenger were found to follow similar tracks. This indicates that the airflow in most of the cabin was steady. It is proposed that the concentration of the droplets in a zone can be obtained by adding the concentrations in the zone from all the exhalations taken place until that time provided with a time shift.