Inhalation of expiratory droplets in aircraft cabin

National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE), School of Mechanical Engineering, Purdue University, West Lafayette, IN, USA.
Indoor Air (Impact Factor: 4.9). 08/2011; 21(4):341-50. DOI: 10.1111/j.1600-0668.2011.00709.x
Source: PubMed


Abstract Airliner cabins have high occupant density and long exposure time, so the risk of airborne infection transmission could be high if one or more passengers are infected with an airborne infectious disease. The droplets exhaled by an infected passenger may contain infectious agents. This study developed a method to predict the amount of expiratory droplets inhaled by the passengers in an airliner cabin for any flight duration. The spatial and temporal distribution of expiratory droplets for the first 3 min after the exhalation from the index passenger was obtained using the computational fluid dynamics simulations. The perfectly mixed model was used for beyond 3 min after the exhalation. For multiple exhalations, the droplet concentration in a zone can be obtained by adding the droplet concentrations for all the exhalations until the current time with a time shift via the superposition method. These methods were used to determine the amount of droplets inhaled by the susceptible passengers over a 4-h flight under three common scenarios. The method, if coupled with information on the viability and the amount of infectious agent in the droplet, can aid in evaluating the infection risk.
The distribution of the infectious agents contained in the expiratory droplets of an infected occupant in an indoor environment is transient and non-uniform. The risk of infection can thus vary with time and space. The investigations developed methods to predict the spatial and temporal distribution of expiratory droplets, and the inhalation of these droplets in an aircraft cabin. The methods can be used in other indoor environments to assess the relative risk of infection in different zones, and suitable measures to control the spread of infection can be adopted. Appropriate treatment can be implemented for the zone identified as high-risk zones.

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    • "Relatively few studies have focused on breathing airflow dynamics. Gupta and colleagues performed a series of experiments to characterise the morphology and flow dynamics of nasal and mouth breathing [21], and followed this by computer simulations of how such breath plumes might disseminate and be inhaled in a fully occupied aircraft cabin [22], [23]. Tang et al. [17] used a real-time, non-invasive, shadowgraph method to visualise the airflows produced during nasal and mouth breathing, talking (counting), coughing, laughing and sneezing healthy volunteers, though this was only a qualitative visualisation study without any quantitative assessment being attempted. "
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    ABSTRACT: Natural human exhalation flows such as coughing, sneezing and breathing can be considered as 'jet-like' airflows in the sense that they are produced from a single source in a single exhalation effort, with a relatively symmetrical, conical geometry. Although coughing and sneezing have garnered much attention as potential, explosive sources of infectious aerosols, these are relatively rare events during daily life, whereas breathing is necessary for life and is performed continuously. Real-time shadowgraph imaging was used to visualise and capture high-speed images of healthy volunteers sneezing and breathing (through the nose - nasally, and through the mouth - orally). Six volunteers, who were able to respond to the pepper sneeze stimulus, were recruited for the sneezing experiments (2 women: 27.5±6.36 years; 4 men: 29.25±10.53 years). The maximum visible distance over which the sneeze plumes (or puffs) travelled was 0.6 m, the maximum sneeze velocity derived from these measured distances was 4.5 m/s. The maximum 2-dimensional (2-D) area of dissemination of these sneezes was 0.2 m(2). The corresponding derived parameter, the maximum 2-D area expansion rate of these sneezes was 2 m(2)/s. For nasal breathing, the maximum propagation distance and derived velocity were 0.6 m and 1.4 m/s, respectively. The maximum 2-D area of dissemination and derived expansion rate were 0.11 m(2) and 0.16 m(2)/s, respectively. Similarly, for mouth breathing, the maximum propagation distance and derived velocity were 0.8 m and 1.3 m/s, respectively. The maximum 2-D area of dissemination and derived expansion rate were 0.18 m(2) and 0.17 m(2)/s, respectively. Surprisingly, a comparison of the maximum exit velocities of sneezing reported here with those obtained from coughing (published previously) demonstrated that they are relatively similar, and not extremely high. This is in contrast with some earlier estimates of sneeze velocities, and some reasons for this difference are discussed.
    PLoS ONE 04/2013; 8(4):e59970. DOI:10.1371/journal.pone.0059970 · 3.23 Impact Factor
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    • "Quanta is a term defined by Wells, 1955 that indicates that if a person inhales one quanta, the probability of his getting infected is 1-1/e. Any of these quantities can be used to define the amount of dose exhaled, then the dose inhaled can be calculated using equation (1) (Gupta et al., 2011b "
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    ABSTRACT: Abstract  Passengers in an aircraft cabin can have different risks of infection from airborne infectious diseases such as influenza, severe acute respiratory syndrome (SARS), and tuberculosis (TB) because of the non-uniform airflow in an aircraft cabin. The current investigation presents a comprehensive approach to assessing the spatial and temporal distributions of airborne infection risk in an aircraft cabin. A case of influenza outbreak was evaluated in a 4-h flight in a twin-aisle, fully occupied aircraft cabin with the index passenger seated at the center of the cabin. The approach considered the characteristics of the exhalation of the droplets carrying infectious agents from the index passenger, the dispersion of these droplets, and the inhalation of the droplets by susceptible passengers. Deterministic and probabilistic approaches were used to quantify the risks based on the amount of inhaled influenza virus RNA particles and quanta, respectively. The probabilistic approach indicated that the number of secondary infection cases can be reduced from 3 to 0 and 20 to 11, for influenza cases if N95 respirator masks are used by the passengers. The approach and methods developed can easily be implemented in other enclosed spaces such as buildings, trains, and buses to assess the infection risk. PRACTICAL IMPLICATIONS: Airborne infectious disease transmission could take place in enclosed environments such as buildings and transport vehicles. The infection risk is difficult to estimate, and very few mitigation methods are available. This study used a 4-h flight as an example in analyzing the infection risk from influenza and in mitigating the risk with an N95 mask. The results will be useful to the airline industry in providing necessary protection to passengers and crew, and the results can also be used for other enclosed spaces.
    Indoor Air 02/2012; 22(5):388-95. DOI:10.1111/j.1600-0668.2012.00773.x · 4.90 Impact Factor
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    ABSTRACT: With advanced air handling systems on modern aircraft and the high level of measles immunity in many countries, measles infection in air travelers may be considered a low-risk event. However, introduction of measles into countries where transmission has been controlled or eliminated can have substantial consequences both for the use of public health resources and for those still susceptible. In an effort to balance the relatively low likelihood of disease transmission among largely immune travelers and the risk to the public health of the occurrence of secondary cases resulting from importations, criteria in the United States for contact investigations for measles exposures consider contacts to be those passengers who are seated within 2 rows of the index case. However, recent work has shown that cabin air flow may not be as reliable a barrier to the spread of measles virus as previously believed. Along with these new studies, several reports have described measles developing after travel in passengers seated some distance from the index case. To understand better the potential for measles virus to spread on an airplane, reports of apparent secondary cases occurring in co-travelers of passengers with infectious cases of measles were reviewed. Medline™ was searched for articles in all languages from 1946 to week 1 of March 2012, using the search terms "measles [human] or rubeola" and ("aircraft" or "airplane" or "aeroplane" or "aviation" or "travel" or "traveler" or "traveller"); 45 citations were returned. Embase™ was searched from 1988 to week 11 2012, using the same search strategy; 95 citations were returned. Papers were included in this review if they reported secondary cases of measles occurring in persons traveling on an airplane on which a person or persons with measles also flew, and which included the seating location of both the index case(s) and the secondary case(s) on the plane. Nine reports, including 13 index cases and 23 apparent secondary cases on 10 flights, were identified in which transmission on board the aircraft appeared likely and which included seating information for both the index (primary) and secondary cases. Separation between index and secondary cases ranged from adjacent seats to 17 rows, with a median of 6 rows. Three flights had more than one index case aboard. Based on previously published data, it is not possible to say how unusual cases of measles transmission among air travelers beyond the usual zone of contact investigation (the row the index case sat in and 2 rows ahead of or behind that row) may be. The fact that several flights had more than one infectious case aboard and that all but two index cases were in the prodromal phase may be of importance in understanding the wider spread described in several of the reviewed reports. Although the pattern of cabin air flow typical of modern commercial aircraft has been considered highly effective in limiting the airborne spread of microorganisms, concerns have been raised about relying on the operation of these systems to determine exposure risk, as turbulence in the cabin air stream is generated when passengers and crew are aboard, allowing the transmission of infectious agents over many rows. Additionally, the characteristics of some index cases may reflect a greater likelihood of disease transmission. Investigators should continue to examine carefully both aircraft and index-case factors that may influence disease transmission and could serve as indicators on a case-by-case basis to include a broader group of travelers in a contact investigation.
    Travel Medicine and Infectious Disease 11/2012; 10(5-6). DOI:10.1016/j.tmaid.2012.10.003 · 1.67 Impact Factor
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