Calculating the potential for within-flight transmission of influenza A (H1N1)

Abstract

BackgroundClearly air travel, by transporting infectious individuals from one geographic location to another, significantly affects the rate of spread of influenza A (H1N1). However, the possibility of within-flight transmission of H1N1 has not been evaluated; although it is known that smallpox, measles, tuberculosis, SARS and seasonal influenza can be transmitted during commercial flights. Here we present the first quantitative risk assessment to assess the potential for within-flight transmission of H1N1.MethodsWe model airborne transmission of infectious viral particles of H1N1 within a Boeing 747 using methodology from the field of quantitative microbial risk assessment.ResultsThe risk of catching H1N1 will essentially be confined to passengers travelling in the same cabin as the source case. Not surprisingly, we find that the longer the flight the greater the number of infections that can be expected. We calculate that H1N1, even during long flights, poses a low to moderate within-flight transmission risk if the source case travels First Class. Specifically, 0-1 infections could occur during a 5 hour flight, 1-3 during an 11 hour flight and 2-5 during a 17 hour flight. However, within-flight transmission could be significant, particularly during long flights, if the source case travels in Economy Class. Specifically, two to five infections could occur during a 5 hour flight, 5-10 during an 11 hour flight and 7-17 during a 17 hour flight. If the aircraft is only partially loaded, under certain conditions more infections could occur in First Class than in Economy Class. During a 17 hour flight, a greater number of infections would occur in First Class than in Economy if the First Class Cabin is fully occupied, but Economy class is less than 30% full.ConclusionsOur results provide insights into the potential utility of air travel restrictions on controlling influenza pandemics in the winter of 2009/2010. They show travel by one infectious individual, rather than causing a single outbreak of H1N1, could cause several simultaneous outbreaks. These results imply that, during a pandemic, quarantining passengers who travel in Economy on long-haul flights could potentially be an important control strategy. Notably, our results show that quarantining passengers who travel First Class would be unlikely to be an effective control strategy.

The risk of airborne influenza transmission in passenger cars

“…An infectious quantum is defined as the dose of droplet nuclei required to cause infection in 63% of susceptible persons. Quanta production rates of infectious individuals have been retrospectively calculated by several epidemiological studies of influenza outbreaks, and we used a value of 67 quanta/h, which represents the approximate median of infectivity estimates for both seasonal influenza [11] and H1N1 [12]. Furthermore, we used the full range of published values; 15 to 128 quanta/h [13], in order to establish the likely range of risk in our simulations.…”

Concentrations and size distributions of airborne influenza A viruses measured indoors at a health centre, a day-care centre and on aeroplanes

“…tested in 14 different daycare centres, Boone & Gerba [9] detected influenza viruses on 23 and 53 per cent of the samples during autumn and spring, respectively. Infected individuals on an aeroplane may spread the influenza virus to other passengers [10]. The Alaska Airlines outbreak [11] has been presented as proof of airborne influenza transmission: a jet with 54 persons aboard was delayed on the ground for 3 h (during which the aeroplane ventilation system was inoperative), and 72 per cent of the passengers who stayed on the aeroplane were infected by an influenza-contracted passenger within 72 h.…”

Airborne Pathogens Transport in an Aircraft Cabin

“…In 1988, Brundage et al [8] showed that febrile illness rates were about 50% higher in sealedwindow than in operable window army barracks. Wagner et al [9] estimated that one passenger infected with H1N1 and travelling in economy class of a commercial aircraft may cause two to five infections during a 5 hour flight and a 5-10 during an 11 hour flight. There are also other studies that analyze experimentally and numerically the airborne pollutant transport within aircrafts (see for example, Liu et al [10], Zhang et al [11], Mazumdar and Chen [12]).…”