Infectivity of influenza virus aerosols

Hood, A. M.

doi:10.1017/s0022172400039619

Cited by 32 publications

(30 citation statements)

References 12 publications

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“…A number of other studies of IVS and RH present more limited data (13,(16)(17)(18), which we also analyzed for the effect of VP on IVS. These data were found to be consistent with the relationship shown in Fig.…”

Section: Resultsmentioning

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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Section: Resultsmentioning

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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“…The average number of log reductions of influenza viruses measured for the three exposure times (15,30, and 60 min) for all combinations of the three temperatures (55°C, 60°C, and 65°C) and three RH levels (25%, 50%, and 75%) are listed in Table 1. Surface inactivation of influenza virus increased with increasing temperature, RH, and exposure time.…”

Section: Resultsmentioning

confidence: 99%

“…The majority of previous studies on the influence of RH on influenza virus survival have been largely focused on survival of influenza virus aerosols rather than influenza virus on surfaces (10,12,14,15,17,26). A single study by Buckland and Tyrrel report a 1.7-log reduction of influenza virus deposited on slides for 2.5 h at room temperature at 20% RH and up to a 3.5-log reduction when RH was increased to 84% (5).…”

Section: Discussionmentioning

confidence: 99%

“…Past research on influenza virus has focused on airborne viruses and generally suggests that survival and/or transmission is facilitated by low RH (10,12,15,17,26,30). A limited number of surface inactivation studies have been performed at environmentally relevant temperatures, ranging from 7 to 32°C (30), and have shown modest reductions in numbers of influenza viruses (5,21).…”

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confidence: 99%

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Role of Absolute Humidity in the Inactivation of Influenza Viruses on Stainless Steel Surfaces at Elevated Temperatures

McDevitt¹,

Rudnick²,

First³

et al. 2010

Appl Environ Microbiol

105

115

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Influenza virus has been found to persist in the environment for hours to days, allowing for secondary transmission of influenza via inanimate objects known as fomites. We evaluated the efficacy of heat and moisture for the decontamination of surfaces for the purpose of preventing of the spread of influenza. Aqueous suspensions of influenza A virus were deposited onto stainless steel coupons, allowed to dry under ambient conditions, and exposed to temperatures of 55°C, 60°C, or 65°C and relative humidity (RH) of 25%, 50%, or 75% for up to 1 h. Quantitative virus assays were performed on the solution used to wash the viruses from these coupons, and results were compared with the solution used to wash coupons treated similarly but left under ambient conditions. Inactivation of influenza virus on surfaces increased with increasing temperature, RH, and exposure time. Reductions of greater than 5 logs of influenza virus on surfaces were achieved at temperatures of 60 and 65°C, exposure times of 30 and 60 min, and RH of 50 and 75%. Our data also suggest that absolute humidity is a better predictor of surface inactivation than RH and allows the prediction of survival using two parameters rather than three. Modest amounts of heat and adequate moisture can provide effective disinfection of surfaces while not harming surfaces, electrical systems, or mechanical components, leaving no harmful residues behind after treatment and requiring a relatively short amount of time.In a recent publication, Shaman and Kohn concluded that absolute humidity, which can be calculated if temperature and relative humidity (RH) are known, is the controlling factor in both the inactivation of influenza virus and the transmission of influenza (27). To arrive at this conclusion, Shaman and Kohn reanalyzed experimental data collected by Lowen et al. and Harper (12,17,18), which covered a rather narrow range of temperatures typical of normal weather conditions, that is, in the range of 5 to 30°C. For this temperature range, the maximum absolute humidity that can occur is 24 g/m 3 . One question that comes to mind is whether this trend of decreasing influenza virus survival with increasing absolute humidity (AH)

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“…Fifteen studies reported persistence of influenza virus in air, 15 in water, 10 in soil or feces, and five on fomites (several studies included multiple matrices). Twelve studies published prior to 1970 (13,22,28,29,32,40,43,49,59,70,74,100) reported influenza virus persistence in air, while the remaining three were published between 1970 and 1990 (35,48,67 (55,87). Of the 77 relevant experiments within the 40 studies, 56 did not describe the key features recommended by the content experts.…”

Section: Resultsmentioning

confidence: 99%

Using the Systematic Review Methodology To Evaluate Factors That Influence the Persistence of Influenza Virus in Environmental Matrices

Irwin

Yoon

Wang

et al. 2011

Appl Environ Microbiol

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, i.e., air, water, soil, feces, and fomites. An electronic search of PubMed, CAB, AGRICOLA, Biosis, and Compendex was performed, and citation relevance was determined according to the aim of the review. Quality assessment of relevant studies was performed using criteria from experts in virology, disease ecology, and environmental science. A total of 9,760 abstracts were evaluated, and 40 appeared to report the persistence of influenza virus in environmental samples. Evaluation of full texts revealed that 19 of the 40 studies were suitable for review, as they described virus concentration measured at multiple sampling times, with viruses detectable at least twice. Seven studies reported persistence in air (six published before 1970), seven in water (five published after 1990), two in feces, and three on surfaces. All three fomite and five air studies addressed human influenza virus, and all water and feces studies pertained to avian influenza virus. Outcome measurements were transformed to half-lives, and resultant multivariate mixed linear regression models identified influenza virus surviving longer in water than in air. Temperature was a significant predictor of persistence over all matrices. Salinity and pH were significant predictors of persistence in water conditions. An assessment of the methodological quality review of the included studies revealed significant gaps in reporting critical aspects of study design.

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Infectivity of influenza virus aerosols

Cited by 32 publications

References 12 publications

Absolute humidity modulates influenza survival, transmission, and seasonality

Absolute humidity modulates influenza survival, transmission, and seasonality

Role of Absolute Humidity in the Inactivation of Influenza Viruses on Stainless Steel Surfaces at Elevated Temperatures

Using the Systematic Review Methodology To Evaluate Factors That Influence the Persistence of Influenza Virus in Environmental Matrices

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