key: cord-1014621-lnrbx95s
authors: Tang, Julian W; Li, Yuguo
title: Transmission of influenza A in human beings
date: 2007-11-26
journal: Lancet Infect Dis
DOI: 10.1016/s1473-3099(07)70268-2
sha: 9f170863c54c51aaab977e093ac9daa463bf2a23
doc_id: 1014621
cord_uid: lnrbx95s

nan

We read with interest the Review by Gabrielle Brankston and colleagues 1 on the transmission of infl uenza A, but were disappointed to fi nd it very biased against any evidence presented in favour of the airborne transmission of infl uenza. One surprising example of this was the authors' discussion of the classic study by Moser and co-workers, 2 which they dismiss in a single sentence: "because of the free movement of passengers throughout the aircraft, close range transmission of infl uenza through droplet or direct contact could not be ruled out". 1 Although we do not dispute the relevance and presence of this phrase in the original study, many other papers (including the reply by Tellier 3 to recent criticism of his earlier Review 4 ) have cited this particular study as more supportive than not, of the airborne transmission of infl uenza. 5 What makes the interpretation of this study by these other authors any less accurate than that of Brankston and colleagues? 1 Another example of bias against evidence of airborne transmission in Brankston and co-workers' Review is their discussion about whether the ferret is a good model for human infl uenza. In fact, the ferret is now one of the preferred small animal models for studying human infl uenza in terms of pathogenesis and transmission. 6 Are the authors now saying that these other researchers are using an inappropriate model for studying human infl uenza?

Regarding droplet dynamics, it is likely that the use of respiratory-assist devices, such as high-fl ow (up to 10-15 L/min) oxygen masks and mechanical ventilation, is likely to increase the potential risk of naturally (as opposed to artifi cially) produced aerosols containing infl uenza, as was suggested during the severe acute respiratory syndrome (SARS) outbreaks of 2003. 7, 8 Also, at one point, Brankston and colleagues seem to underinterpret one of their own references, 9 in which particles of 6-10 µm diameter are listed as being able to remain suspended for "several hours" while falling a height of 3 m during which "deposition in nasal passages" is possible. Even accepting their statement that coughing mostly produces particles greater than 8 µm, this does not preclude coughed particles of sizes 8-10 µm being able to remain suspended and transmit infection over long distances. They themselves admit that "there is no exact particle size cut-off at which pathogen transmission changes from exclusively droplet to airborne, or vice versa". The exact proportion of diff erent sized droplets produced in a cough will diff er between individuals in diff erent situations. After the droplets have left the mouth, their size will also be aff ected by the ambient temperature and relative humidity. For these reasons at least, Brankston and colleagues' generalisation that coughed particles are too large to sustain airborne infl uenza transmission is unacceptable.

We realise that the practical and economical consequences of accepting infl uenza as an airborne infection are signifi cant. However, this should not make us deliberately downplay or underinterpret any data that are supportive of this route of transmission. Hence, we would off er the counterpoint that this issue is not closed and echo Oshitani 10 who stated that "the proportion of infl uenza infections that can be acquired by the airborne transmission is largely unknown". The potential role for airborne infl uenza transmission, therefore, still remains an important issue in pandemic infl uenza preparedness.

Transmission of infl uenza A in human beings

An outbreak of infl uenza aboard a commercial airliner

Questioning aerosol transmission of infl uenza-author's reply

Review of aerosol transmission of infl uenza A virus

Epidemiology and prevention of pediatric viral respiratory infections in health-care institutions

Lack of transmission of H5N1 avianhuman reassortant infl uenza viruses in a ferret model

Airfl ows around oxygen masks: a potential source of infection?

Noninvasive positive-pressure ventilation: an experimental model to assess air and particle dispersion

Protecting the faces of health care workers: knowledge gaps and research priorities for eff ective protection against occupationally-acquired respiratory infectious diseases

Potential benefi ts and limitations of various strategies to mitigate the impact of an infl uenza pandemic