Questioning Aerosol Transmission of Influenza

Lemieux, Camille; Brankston, Gabrielle; Gitterman, Leah; Hirji, Zahir; Gardam, Michael

doi:10.3201/eid1301.061202

Cited by 47 publications

(43 citation statements)

References 8 publications

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“…Reviews of influenza transmission among human populations have concluded that transmission is by contact and droplet spray [9], [10] while others conclude that aerosol transmission contributes significantly to spread of infection [11], [12]. Transmissibility is currently estimated from the spread of influenza in relatively closed populations and is expressed as the number of secondary infections derived from one contagious person (basic reproductive number R 0 ).…”

Section: Introductionmentioning

confidence: 99%

Exhaled Aerosol Transmission of Pandemic and Seasonal H1N1 Influenza Viruses in the Ferret

et al. 2012

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Person-to-person transmission of influenza viruses occurs by contact (direct and fomites) and non-contact (droplet and small particle aerosol) routes, but the quantitative dynamics and relative contributions of these routes are incompletely understood. The transmissibility of influenza strains estimated from secondary attack rates in closed human populations is confounded by large variations in population susceptibilities. An experimental method to phenotype strains for transmissibility in an animal model could provide relative efficiencies of transmission. We developed an experimental method to detect exhaled viral aerosol transmission between unanesthetized infected and susceptible ferrets, measured aerosol particle size and number, and quantified the viral genomic RNA in the exhaled aerosol. During brief 3-hour exposures to exhaled viral aerosols in airflow-controlled chambers, three strains of pandemic 2009 H1N1 strains were frequently transmitted to susceptible ferrets. In contrast one seasonal H1N1 strain was not transmitted in spite of higher levels of viral RNA in the exhaled aerosol. Among three pandemic strains, the two strains causing weight loss and illness in the intranasally infected ‘donor’ ferrets were transmitted less efficiently from the donor than the strain causing no detectable illness, suggesting that the mucosal inflammatory response may attenuate viable exhaled virus. Although exhaled viral RNA remained constant, transmission efficiency diminished from day 1 to day 5 after donor infection. Thus, aerosol transmission between ferrets may be dependent on at least four characteristics of virus-host relationships including the level of exhaled virus, infectious particle size, mucosal inflammation, and viral replication efficiency in susceptible mucosa.

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Section: Introductionmentioning

confidence: 99%

Exhaled Aerosol Transmission of Pandemic and Seasonal H1N1 Influenza Viruses in the Ferret

et al. 2012

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“…The exact mechanisms by which transmission occurs are still unclear, but is believed to involve multiple routes, including respiratory droplets and direct/indirect contact [1] with secretions or fomites. Aerosol transmission may also occur, but controversy surrounds this [2] and some further evidence of aerosol transmission has recently been put forward [3]. This is an important issue as the mechanism of transmission is always a key factor in infection control planning.…”

Section: Introductionmentioning

confidence: 99%

Could influenza transmission be reduced by restricting mass gatherings? Towards an evidence-based policy framework

Ishola¹,

Phin²

2011

JEGH

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“…The relative importance of these 4 transmission modes remains a subject of much debate (1)(2)(3)(4)(5)(6)(7).…”

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confidence: 99%

Absolute humidity modulates influenza survival, transmission, and seasonality

Shaman

Kohn²

2009

Proc. Natl. Acad. Sci. U.S.A.

919

968

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Influenza A incidence peaks during winter in temperate regions. The basis for this pronounced seasonality is not understood, nor is it well documented how influenza A transmission principally occurs. Previous studies indicate that relative humidity (RH) affects both influenza virus transmission (IVT) and influenza virus survival (IVS). Here, we reanalyze these data to explore the effects of absolute humidity on IVT and IVS. We find that absolute humidity (AH) constrains both transmission efficiency and IVS much more significantly than RH. In the studies presented, 50% of IVT variability and 90% of IVS variability are explained by AH, whereas, respectively, only 12% and 36% are explained by RH. In temperate regions, both outdoor and indoor AH possess a strong seasonal cycle that minimizes in winter. This seasonal cycle is consistent with a wintertime increase in IVS and IVT and may explain the seasonality of influenza. Thus, differences in AH provide a single, coherent, more physically sound explanation for the observed variability of IVS, IVT and influenza seasonality in temperate regions. This hypothesis can be further tested through future, additional laboratory, epidemiological and modeling studies.virus survival ͉ vapor pressure ͉ droplet nuclei ͉ aerosol T here are 4 suspected modes of influenza virus transmission (IVT) (1): (i) transmission through direct physical contact with an infected individual, (ii) transmission via intermediate, often inanimate, objects (i.e., fomites), (iii) transmission via droplets expelled from infected individuals (e.g., by sneezing or coughing) that deposit on nasal or oral mucosa of a susceptible individual, and (iv) airborne transmission via expelled particles Ͻ2.5 m in radius, which are referred to as droplet nuclei and remain suspended in air as aerosols for extended periods of time. The relative importance of these 4 transmission modes remains a subject of much debate (1-7).A recent laboratory experiment examining influenza A transmission among guinea pig hosts suggests that airborne transmission may indeed be an important mode of IVT (8). In this study, groups of 4 infected and 4 susceptible hosts were maintained in separate cages at different temperature and relative humidity (RH) conditions. Transmission rates, measured as the percentage of susceptible hosts infected, were found to increase at lower RH. Two hypotheses were proposed to explain this relationship (8): (i) virus-laden droplet nuclei are more efficiently produced at lower RH because of increased evaporation of expelled droplet particles, such that more virus remains airborne longer; (ii) influenza virus survival (IVS) increases as RH decreases, such that the airborne virus remains viable longer at lower RH.Heretofore, analyses of the effects of humidity on both IVS and IVT have focused on RH as the metric for air moisture. RH is the ratio of the actual water vapor pressure of the air to the equilibrium, or saturation, vapor pressure of the air. Because saturation vapor pressure increases exponentially as te...

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Questioning Aerosol Transmission of Influenza

Cited by 47 publications

References 8 publications

Exhaled Aerosol Transmission of Pandemic and Seasonal H1N1 Influenza Viruses in the Ferret

Exhaled Aerosol Transmission of Pandemic and Seasonal H1N1 Influenza Viruses in the Ferret

Could influenza transmission be reduced by restricting mass gatherings? Towards an evidence-based policy framework

Absolute humidity modulates influenza survival, transmission, and seasonality

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