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Aerosol Susceptibility of Influenza Virus to UV-C Light


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The person-to-person transmission of influenza virus, especially in the event of a pandemic caused by a highly virulent strain of influenza, such as H5N1 avian influenza, is of great concern due to widespread mortality and morbidity. The consequences of seasonal influenza are also substantial. Because airborne transmission appears to play a role in the spread of influenza, public health interventions should focus on preventing or interrupting this process. Air disinfection via upper-room 254-nm germicidal UV (UV-C) light in public buildings may be able to reduce influenza transmission via the airborne route. We characterized the susceptibility of influenza A virus (H1N1, PR-8) aerosols to UV-C light using a benchtop chamber equipped with a UVC exposure window. We evaluated virus susceptibility to UV-C doses ranging from 4 to 12 J/m2 at three relative humidity levels (25, 50, and 75%). Our data show that the Z values (susceptibility factors) were higher (more susceptible) to UV-C than what has been reported previously. Furthermore, dose-response plots showed that influenza virus susceptibility increases with decreasing relative humidity. This work provides an essential scientific basis for designing and utilizing effective upper-room UV-C light installations for the prevention of the airborne transmission of influenza by characterizing its susceptibility to UV-C.
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Aerosol Susceptibility of Influenza Virus to UV-C Light
James J. McDevitt,
Stephen N. Rudnick,
and Lewis J. Radonovich
Harvard School of Public Health, Boston, Massachusetts, USA,
and National Center for Occupational Health and Infection Control, Veterans Health Administration,
Gainesville, Florida, USA
The person-to-person transmission of influenza virus, especially in the event of a pandemic caused by a highly virulent strain of
influenza, such as H5N1 avian influenza, is of great concern due to widespread mortality and morbidity. The consequences of
seasonal influenza are also substantial. Because airborne transmission appears to play a role in the spread of influenza, public
health interventions should focus on preventing or interrupting this process. Air disinfection via upper-room 254-nm germi-
cidal UV (UV-C) light in public buildings may be able to reduce influenza transmission via the airborne route. We characterized
the susceptibility of influenza A virus (H1N1, PR-8) aerosols to UV-C light using a benchtop chamber equipped with a UVC ex-
posure window. We evaluated virus susceptibility to UV-C doses ranging from 4 to 12 J/m
at three relative humidity levels (25,
50, and 75%). Our data show that the Z values (susceptibility factors) were higher (more susceptible) to UV-C than what has
been reported previously. Furthermore, dose-response plots showed that influenza virus susceptibility increases with decreasing
relative humidity. This work provides an essential scientific basis for designing and utilizing effective upper-room UV-C light
installations for the prevention of the airborne transmission of influenza by characterizing its susceptibility to UV-C.
Seasonal influenza is a major cause of morbidity and mortality
in the United States and throughout the world. Each year,
influenza accounts for about 3 million hospital days, 31 million
outpatient visits, and $10 billion in excess costs in the United
States. These consequences are most predominant in the very
young and the elderly (22). As demonstrated by the 2009 H1N1
influenza pandemic, influenza can spread rapidly in populations,
and the development of vaccines can take months to accomplish
(11). Furthermore, the use of nonpharmaceutical interventions
appears to have had limited effectiveness (11). In the event of the
pandemic spread of highly virulent strains of influenza, such as
H5N1 bird flu, which has recently shown a mortality rate of ap-
proximately 60%, effects could be disastrous (5, 26). For these
reasons, effective interventions to prevent the transmission of in-
fluenza are needed.
Contemporary science continues to study and understand the
modes used by influenza virus to spread from person to person.
There is debate about whether influenza virus is transmitted via
fine aerosols that are airborne, through exposure to large ballistic
droplets, or contact with fomites (3, 29). Understanding the route
of transmission is critical for implementing the best control strat-
egies. There is considerable evidence for the airborne transmission
of influenza via fine aerosols: influenza aerosols have been shown
to remain infective in laboratory experiments; the aerosol trans-
mission of influenza has also been shown to occur in animal and
human volunteer studies (1, 17); influenza nucleic acids have been
associated with fine particles in the exhaled breath of persons in-
fected with influenza virus (2, 7, 15, 16); and human epidemiology
studies have associated influenza transmission with airborne
routes (20, 23). As such, interventions to prevent influenza trans-
mission must go beyond the traditional dogma of cough etiquette,
hand hygiene, and social distancing. Due to their very low termi-
nal settling velocity, infectious fine particles, wafted by air cur-
rents, would be expected to remain airborne for hours. One inter-
vention proposed to be effective is UV irradiation, also called
UV-C light, emitted from specialized lamps placed near the ceiling.
The germicidal effect of light in the UV-C electromagnetic
spectrum (specifically 254-nm light) has been recognized for
some time. The susceptibility of microorganisms to UV-C light
varies and has been summarized in previous investigations (14).
Microorganism susceptibility to UV-C light is traditionally
thought to follow first-order kinetics according to the equation
, where F
is the fraction remaining, C
is microorganism concentration with UV exposure, C
is mi-
croorganism concentration without UV exposure, Zis the suscep-
tibility parameter expressed in m
/J, and Dis the dose of UV-C in
(4, 8, 18). These susceptibility parameters, or Z values, do not
appear to be static but vary with environmental conditions, such
as relative humidity (RH) (12, 13, 18). There is also evidence that
the susceptibility of microorganisms to UV-C light does not nec-
essarily follow first-order kinetics (18). Thus, it is necessary to
determine Z values in a defined and controlled experimental sys-
tem to predict UV-C effectiveness, determine the amount of
UV-C energy required for intervention, and develop models of
UV-C effectiveness.
Traditionally, UV-C light has been used to sanitize air using
UV-C light emitted by lamps located in the upper portions of
rooms (8). High-intensity light restricted to the upper part of the
room by special louvered fixtures inactivates microorganisms as
they circulate through the room via air currents. Due to the lou-
vered fixtures, the UV levels in the lower, occupied part of the
room remain at safe levels (25). The aim of our investigation was
to determine Z values for influenza virus aerosols at low, medium,
and high relative humidity.
Virus preparation. A suspension of influenza virus (A/PR/8/34 H1N1),
which was purchased from Advanced Biotechnologies Inc. (Columbia,
Received 26 September 2011 Accepted 22 December 2011
Published ahead of print 6 January 2012
Address correspondence to James J. McDevitt,
Copyright © 2012, American Society for Microbiology. All Rights Reserved.
1666 0099-2240/12/$12.00 Applied and Environmental Microbiology p. 1666 –1669
MD), was thawed, divided into single-use portions, and stored at 80°C
until needed.
Virus infectivity assay. A fluorescent focus reduction assay was used
to enumerate numbers of infective viruses and has been described previ-
ously (9, 28). Briefly, infected Madin-Darby canine kidney (MDCK) cells
(ATTC CCL-34) containing influenza A nucleoproteins were labeled with
influenza A virus nucleoprotein antibody (Abcam, Cambridge, MA) and
subsequently labeled with rhodamine-labeled goat anti-mouse IgG (Jack-
son ImmunoResearch Laboratories, West Grove, PA). The number of
cells having resulting fluorescent foci (measured in fluorescent focus units
[FFU]) was counted using an Olympus CKX-41 inverted fluorescence
microscope (200total power; Olympus, Center Valley, PA). The num-
ber of FFU per sample was computed based on dilution factors and the
fraction of the well counted.
Benchtop UV-C aerosol exposure chamber. Influenza aerosols were
generated by adding 0.075 ml of undiluted influenza virus and 75 ml of
buffer (Dulbecco’s phosphate-buffered saline with calcium and magne-
sium containing 0.1% bovine serum albumin) into a high-output ex-
tended aerosol respiratory therapy (HEART) nebulizer (Westmed, Tuc-
son, AZ) and pressurizing at 69 kPa. The nebulizer output was mixed with
dry or humidified air (to achieve the desired RH level) in a 7.5-liter cham-
ber prior to delivery to the aerosol exposure chamber. The details of the
one-pass, dynamic aerosol test system were described previously (18). RH
and temperature in the chamber (measured via an Omega RH32 temper-
ature and relative humidity meter [Omega Engineering Inc., Stamford,
CT]) were measured prior to entry into the UV-C exposure section. UV-C
was generated by six 36-W low-pressure mercury lamps (254-nm light;
Lumalier, Memphis, TN), and screens were placed between the UV-C
light source and the exposure window to attenuate UV-C output and dose
within the exposure chamber. UV-C irradiance in the chamber was mea-
sured through a fused quartz port in the bottom of the UV-C exposure
section of the chamber using an IL 1400A UV light meter (International
Light, Peabody, MA). The irradiance levels used were based on initial
influenza virus dose-response experiments performed in our chamber
and the detection limits of our infectivity assay. The UV-C dose was com-
puted by multiplying the UV-C irradiance by the exposure time. The
exposure time was computed by dividing the volume of the chamber by
the airflow rate.
Air was drawn through the chamber by a pump at 25 liters/min
through a manifold attached to 2 SKC Biosamplers (SKC Inc., Eighty
Four, PA), each operating at 12.5 liters/min. Each Biosampler contained
20 ml of virus buffer (Dulbecco’s phosphate-buffered saline with calcium
and magnesium containing 0.1% bovine serum albumin). A HEPA filter
was connected after the samplers to remove fugitive aerosols before the
airstream entered the pump. When sampling was not in progress, the
aerosol-laden airstream running through the chamber was bypassed
around the samplers, and the 25-liter/min flow was directed to the HEPA
filter. The entire apparatus was set up inside a 6-foot class II biosafety
cabinet and maintained under negative pressure with respect to the cabi-
net interior.
The nebulizer was run for 20 min before sampling to ensure that
concentrations within the chamber had stabilized. Samples were collected
by passing the entire chamber airflow through the Biosamplers for a pe-
riod of 15 min. Sample pairs were collected that consisted of a sample with
the UV-C lights on followed by a control sample with the UV-C lights off.
Triplicate sample pairs were collected for combinations of UV-C dose
(ranging from 4 to 12 J/m
) and RH (25 to 27%, 50 to 54%, and 81 to
84%). After each sampling the BioSamplers were removed from the
chamber, the volume of collection liquid was measured, and virus collec-
tion fluid was stored at 4°C for a maximum of 3 h prior to performing the
infectivity assay. The BioSamplers were decontaminated with 10% bleach,
rinsed with 70% ethanol, and dried before reusing.
The fraction of virus surviving for each sample pair was calculated by
dividing the number of FFUs per sample with the UV-C lights on by the
number FFUs per sample with the UV-C lights off.
Linear regression through the origin was used to estimate the Z values
for each level of humidity. The log(F
) was our outcome variable, and
the dose level was our response. The estimated coefficient of the regression
line then was our estimate of the Z value. The bootstrap method was used
to determine whether the estimated Z values differed. Given any two Z
values that were tested, we bootstrapped 1,000 pairs of resampled data sets
from the original data at each humidity level, reran the regression models,
and calculated the difference between the estimated coefficients. This gave
us an estimate of the distribution of the difference between the coeffi-
cients. We calculated a Pvalue for each difference by using this distribu-
tion to test the hypothesis that the true difference is equal to 0. Statistical
analysis was performed using SAS 9.1 (SAS Institute, Cary, NC).
The average airborne concentration of influenza virus in the
chamber as measured by the focus assay was 5.62 10
FFU per
liter of air, which corresponded to 2,636 FFU per well on the
96-well plate. The fractional survival of influenza aerosols was
measured in triplicate for combinations of three ranges of relative
humidity (low, 25 to 27%; medium, 50 to 54%; and high, 81 to
84%) and 6 UV doses ranging from 4.9 to 15.0 J/m
(Fig. 1). Using
our experimental system, we measured influenza reductions as
low as 98.2% by comparing samples with the UV light on to sub-
sequent samples control samples with the UV light off. The coef-
ficients of variation between triplicate experiments ranged from
0.04 to 0.45 with a median of 0.13. The fractional survival of in-
fluenza aerosolized at low (25 to 27%), medium (50 to 54%), or
high (81 to 84%) RH is shown in Fig. 1. We calculated Z values of
0.29, 0.27, and 0.22 m
/J for low, medium, and high relative hu-
midity levels, respectively (Table 1). Generally, as the RH in-
creased the Z value decreased. The dose-response relationship ap-
pears linear when the log of the fractional survival is plotted
against the UV-C dose and reflects first-order decay. Linear re-
gression models fit the data well, as reflected by R
values, which
were at least 0.95. Bootstrap results of the 1,000 samples show that
all Z values are significantly different from each other (P
The Z values determined for influenza aerosols in our study sug-
gest that influenza will be effectively inactivated during exposure
to upper-room UV-C. The Z value reported for influenza virus is
within the range of those reported for Mycobacterium tuberculosis.
Upper-room UV-C has been shown to be highly effective in lab-
oratory studies and has been proposed to control exposures to
tuberculosis (6, 12, 21, 24, 27). The influenza Z values were much
higher (i.e., influenza is more susceptible to UV-C) than those
reported for hardy spores, such as those from Bacillus anthracis
(Table 2) (4, 14).
The Z values reported herein all are higher than those reported
previously for influenza virus aerosols in a review by Kowalski et
al. (14), which was based on research by Jensen (10), and suggest
an increased efficacy of UV-C for deactivating influenza virus.
Jensen’s experiments were not designed to measure a Z value for
influenza, and in fact he did not calculate a Z value (18). However,
by making assumptions that were not explicitly supported by Jen-
sen’s description of his experiments, Kowalski was able to calcu-
late a Z value of 0.15 m
/J (18). The differences in Z values between
our data and previously reported data, although modest, may cor-
respond to large differences in virus survival. For example, for a
Influenza UV-C Light
March 2012 Volume 78 Number 6 1667
dose of 6 J/m
a Z value of 0.15 m2/J would result in a 60% reduc-
tion, while a Z value of 0.25 would result in a 77% reduction.
The Z values for influenza virus were statistically different as a
function of RH. These differences showing that influenza aerosols
are less susceptible to UV at higher RH than at lower RH have been
noted in previous UV susceptibility studies for other organisms
(18, 19). In climate-controlled, indoor environments, high RH
values near 75% may be unusual, but in areas without environ-
mental controls UV effectiveness may decrease in the presence of
elevated RH. In these instances where UV-C may be a cost-
effective intervention to reduce influenza exposure, more UV-C
energy may be required.
In recent studies of pox virus susceptibility to UV-C light, the
decay was not linear (18) but rather fit a model where a log-
normal distribution of susceptibilities described virus susceptibil-
ity. These differences may be due to the differences between pox
viruses and influenza virus. Pox viruses are large DNA viruses with
a high degree of structure, whereas influenza viruses are smaller,
simpler, RNA viruses. UV-C light may have different interactions
with nucleic acids to form photodimers, with thiamine found in
DNA and uracil found in RNA, and this may be the source of the
difference in dose-response.
The hospital environment is a location where the unchecked
transmission of influenza virus infection may lead to a hospital-
associated disease outbreak (26, 27). Despite increasing attention
to hospital infection control precautions in recent years, the ex-
posure of health care workers, patients, and visitors to influenza
and other respiratory infections remains a substantial problem
(28). Among the most formidable hospital-associated outbreaks is
one involving a highly virulent virus, such as the H5N1 virus cur-
rently circulating in Eurasia that is known to cause death in an
alarming fraction of its victims (29). To accommodate a surge in
patients needing health care during a severe pandemic, hospitals
are expected to house infected patients in groups consisting of
those with confirmed or suspected pandemic infection. In this
scenario, patients may be held in close proximity to each other on
a designated ward (section) of the facility. Limited numbers of
negative-pressure isolation rooms will be available, producing a
crowded environment with substantial airflow limitations.
Upper-room UV-C light could be utilized in this and many other
pandemic scenarios for air disinfection. Lindsley et al. and Bal-
chere et al. detected influenza virus nucleic acid associated with
fine particles in an emergency department and throughout a
health care facility (2, 15). Although the presence of nucleic acid
does not confirm the presence of infectious viruses, it is strong
evidence that viruses are being released into the air. The use of
upper-room UV-C light would provide cost-effective air disinfec-
tion in settings where it would not be feasible to use engineering
controls, such as increased ventilation rates or filtration (4). Fur-
thermore, the use of upper-room UV would not be limited to
controlling the spread of influenza virus, as it would also control
the spread of other airborne infectious agents (many of which are
susceptible to UV-C light) (14).
TABLE 2 Z values reported for various microorganisms
Microorganism Z value (m
Influenza A virus 0.15
Mycobacterium tuberculosis 0.10–0.48
Bacillus anthracis 0.031
Data are from Kowalski et al. (14).
FIG 1 UV-C susceptibilities of influenza virus aerosols at 25 to 27%, 50 to 54%, and 81 to 84% RH (each data point is the average from triplicate experimental
trials; error bars denote one standard deviation).
TABLE 1 Estimated Z values for influenza aerosols determined at low,
medium, and high relative humidity
RH range (%)
Estimated Z
95% confidence
Lower Upper
25–27 0.29 0.27 0.31 0.985
50–54 0.27 0.26 0.31 0.991
81–84 0.22 0.21 0.23 0.992
McDevitt et al.
1668 Applied and Environmental Microbiology
Relative humidity is one important variable which may influ-
ence the germicidal activity of UV-C light against viruses. Nebu-
lization method, sampling time, aerosol concentration, and dose
are other factors which may play an important role in the germi-
cidal activity of UV-C light. The characterization of these factors
was beyond the scope of our study but warrants future investiga-
Conclusions. By characterizing the susceptibility of influenza
virus to UV-C exposure, this work provides an essential scientific
basis for designing effective upper-room UV-C installations for
the prevention of influenza virus infection transmitted from per-
son to person via an airborne route. The Z values determined for
influenza virus were higher (i.e., greater susceptibility to UV-C)
than those previously reported. Additionally, UV-C effectiveness
was shown to decrease with increasing relative humidity.
We thank Jinyize Wang for her work in the laboratory.
The opinions expressed in this article are those of the authors and do
not necessarily reflect the opinions or positions of the Department of
Veterans Affairs, the Office of Public Health, or the National Center for
Occupational Health and Infection Control.
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... A intensidade do dano às biomoléculas depende do binômio densidade de potência e tempo de exposição, i. e., densidades de potência maiores são capazes de inativar os microrganismos em um tempo menor. Estudos anteriores mostraram que diversas espécies de vírus, incluindo-se os causadores de doenças respiratórias, como o HIN1 e os coronavírus, são facilmente inativados pela radiação UV-C emitida por lâmpadas germicidas (1,2,9,26,27). De maneira geral, os vírus são muito menos resistentes à radiação UV-C do que outros microrganismos patogênicos, como fungos e bactérias (27). ...
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The coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The infection is caused when Spike-protein (S-protein) present on the surface of SARS-CoV-2 interacts with human cell surface receptor, Angiotensin-converting enzyme 2 (ACE2). This binding facilitates SARS-CoV-2 genome entry into the human cells, which in turn causes infection. Since the beginning of the pandemic, many different therapies have been developed to combat COVID-19, including treatment and prevention. This review is focused on the currently adapted and certain other potential therapies for COVID-19 treatment, which include drug repurposing, vaccines and drug-free therapies. The efficacy of various treatment options is constantly being tested through clinical trials and in vivo studies before they are made medically available to the public.
... For both conditions, the virus may experience drying (desiccation). Desiccation, which will result from exposure to air and will be influenced by relative humidity (RH), is known to represent a form of stress for most microbes and viruses, and it may alter their sensitivity to other forms of environmental stress, including UV-C exposure, as illustrated in Fig. 3 for coliphage MS2 [28][29][30][31][32]. Similar trends have been reported for other aerosolized viruses, including vaccinia virus and influenza H1N1 virus [33,34]. However, it should be noted that the effects of RH on coronaviruses and other airborne or surfaceassociated viral pathogens remain somewhat unclear, in that some studies have indicated that these viruses survive longer at low RH [35][36][37], while others indicate that they survive longer at high RH [38], and still others indicate a non-monotonic association between virus survival and RH [39] or no correlation at all [40]. ...
... From several previous investigations, the complexity of estimating the antimicrobial efficacy of UVGI can be attributed to environmental factors such as relative humidity (Ko et al., 2000;Lau et al., 2009), temperature , and airflow pattern . Additionally, various researchers have reported the influence of UV fluencethe product of UV irradiance (W/m 2 ) and exposure time (s) - (Jensen, 1964;Tseng and Li, 2005;First et al., 2007;McDevitt et al., 2007McDevitt et al., , 2008McDevitt et al., , 2012Rudnick and First, 2007;Cutler et al., 2012;Verreault et al., 2015;Lin et al., 2017;Welch et al., 2018;Buonanno et al., 2020;Nunayon et al., 2020a), location of the UVGI system (Li et al., 2010;Sung and Kato, 2011;Nunayon et al., 2022), and source of pathogens (Nunayon et al., 2022) on the efficacy of UVGI systems. Moreover, few scholars reported the relationship between bioaerosols' optical properties and the efficacy of UVGI (Martínez Retamar et al., 2019). ...
... A 'single-pass' experimental chamber was utilized to determine the efficacy of UV and blue light-based technologies on aerosolized virus; this apparatus has been used in earlier inactivation studies of various airborne microorganisms (Ko et al., 2000;McDevitt et al., 2012;McDevitt et al., 2007). The body of the chamber is constructed with stainless steel and consists of three parts: 1) the head (165x165x343 mm), 2) the main body (63x305x381 mm), and 3) the tail (42x305x25 mm). ...
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The COVID-19 pandemic has created an urgent need to utilize existing and develop new intervention technologies for SARS-CoV-2 inactivation on surfaces and in the air. Ultraviolet (UV) technology has been shown to be an effective antimicrobial intervention. Here a study was conducted to determine the efficacy of commercially available UV and blue light-based devices for inactivating HCoV-229E, a surrogate of SARS-CoV-2. The results indicate that two UV devices designed for surface disinfection, with doses of 8.07 µJ/cm² for the 254 nm device and 20.61 µJ/cm² for the 275 nm device, were efficient in inactivating 4.94 logs of surface inoculated HCoV-229E. Additionally, a 222 nm UV device with intended ceiling-based operation was effective in inactivating 1.7 logs of the virus inoculated on surface, with a dose of 6 mJ/cm². A ceiling-based device designed to emit blue light at 405 nm was found to produce 89% reduction in HCoV-229E inoculated on a surface for a dose of 78 J/cm². Finally, the UV based 222 nm device was found to produce a 90% reduction in the concentration of airborne HCoV-229E, at a 55 µJ/cm² dose. These results are indicative of the great potential of using UV based technology for the control of SARS-CoV-2. Implications: An important avenue of arresting COVID-19 and future pandemics caused by infectious pathogens is through environmental disinfection. To this effect, the study presented here evaluates commercially available UV and blue light based antimicrobial devices for their ability to kill the human coronavirus HCoV-229E, a surrogate of SARS-CoV-2, on surfaces and in air. The results indicate that two handheld UV devices produced complete inactivation of surface viral inoculum and a UVC ceiling based device produced 1 log reduction in HCoV-229E in air. These results imply the efficacy of UV technology as an antimicrobial tool, especially for rapid disinfection of indoor air.
... Under laboratory conditions, UVGI has been shown to be effective against a suite of microorganisms including coronaviruses [16], vaccinia [17], myco-bacteria [18] and influenza [19]. In many viral outbreaks, transmission occurs through contaminated surfaces. ...
... Under laboratory conditions, UVGI has been shown to be effective against a suite of microorganisms including coronaviruses [16], vaccinia [17], myco-bacteria [18] and influenza [19]. In many viral outbreaks, transmission occurs through contaminated surfaces. ...
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Since influenza and coronaviruses are currently deadly and emerging threats worldwide, better treatment, remediation and prevention options are needed. In that regard, a basic understanding of severe acute respiratory syndrome (SARS)-CoV-2/COVID-19 (Betacoronaviridae) and other viral pathogen mechanisms of transmission are expected. Unfortunately, unprecedented, and growing distrust of vaccines and even masks or personal protective equipment (PPE) in the United States and elsewhere presents itself as an added challenge. We postulate that development of improved and highly effective prophylactic measures, together with new life-saving therapies that do inhibit or otherwise treat infection of SARS-CoV-2, influenza and other viral pathogens, could be an adjunct measure to globally protect vulnerable individuals from pandemic threats. In this review, we share what we learned from the past COVID experience to offer a multifactorial and improved approach to current and future pandemic infections or threats using low-cost means.
Lactic acid, a small α-hydroxyacid, is ubiquitous in both indoor and outdoor environments. Recently, the photochemistry of lactic acid has garnered interest among the abiotic organic chemistry community as it would have been present in abiotic settings and photoactive with the high-energy solar radiation that would have been available in the low oxygen early Earth environment. Additionally, we propose that the photochemistry of lactic acid is relevant to modern Earth during indoor ultraviolet-C (UVC) sterilization procedures as lactic acid is emitted by humans and is thus prevalent in indoor environments where UVC sterilization is increasingly being used. Here, we study the oxygen effect on the gas phase photolysis of lactic acid using Fourier-transform infrared (FTIR) spectroscopy and isotopically labeled oxygen (18O2). We find that the major products of gas phase lactic acid photolysis are CO2, CO, acetaldehyde, and acetic acid. Furthermore, these products are the same with or without added oxygen, but the partial pressures of produced CO2, CO, and acetaldehyde increase with the amount of added oxygen. Notably, the added oxygen is primarily incorporated into produced CO2 and CO, while little or none is incorporated into acetaldehyde. We combine the results presented here with those in the literature to propose a mechanism for the gas phase photolysis of lactic acid and the role of oxygen in this mechanism. Finally, we compare the output of a krypton-chloride excimer lamp (λ = 222 nm), one of the lamps proposed for UVC sterilization procedures, to the absorption of lactic acid. We show that lactic acid would be photoactive during UVC sterilization procedures, and we use the gas phase results presented here and aqueous lactic acid photolysis results previously published to assess potential byproducts from lactic acid reactions during UVC sterilization procedures.
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Prolonged human-crewed missions on the Moon are foreseen as a gateway for Mars and asteroid colonisation in the next decades. Health risks related to long-time permanence in space have been partially investigated. Hazards due to airborne biological contaminants are possible. A possible way to perform pathogens' inactivation is by employing the shortest wavelength range of Solar ultraviolet radiation, the so-called germicidal range. On Earth, it is totally absorbed by the atmosphere and does not reach the surface. In space, such UV solar component is present and effective germicidal irradiation for airborne pathogens' inactivation can be achieved inside habitable outposts through a combination of highly reflective internal coating and optimised geometry of the air ducts. The Solar Ultraviolet Light Collector for Germicidal Irradiation on the Moon is a project whose aim is to collect Ultraviolet solar radiation and use it as a source to sanitise the re-circulating air of the human outposts. The most favourable positions where to place these collectors are over the peaks at the Moon's poles, which have the peculiarity of being exposed to solar radiation most of the time. On August 2022, NASA communicated to have identified 13 candidate landing regions near the lunar South Pole for Artemis missions. Another advantage of the Moon is its low inclination to the ecliptic, which maintains the Sun’s apparent altitude inside a reduced angular range. For this reason, Ultraviolet solar radiation can be collected through a simplified Sun's tracking collector or even a static collector and used to sanitise the recycled air. Fluid-dynamic and optical simulations have been performed to support the proposed idea. The expected inactivation rates for some airborne pathogens, either common or found on the International Space Station, are reported and compared with the proposed device efficiency. The results show that it is possible to use Ultraviolet solar radiation directly for air sanitation inside the lunar outposts and deliver a healthy living environment to the astronauts.
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As a result of the recent resurgence in tuberculosis (TB) and the increasing incidence of multidrug-resistant TB, there has been renewed interest in engineering controls to reduce the spread of TB and other airborne infectious diseases in high-risk settings. Techniques such as the use of lamps that produce ultraviolet germicidal radiation may reduce exposure to infectious agents by inactivating or killing microorganisms while they are airborne. We designed and evaluated a test method to quantitatively estimate the efficacy of germicidal lamps, in conjunction with dilution ventilation, for reducing the concentration of viable airborne bacteria. Bacterial particles were generated in a 36m3 room and collected with midget impingers at 5-7 locations. The effectiveness of the control technique was determined by comparing concentrations of culturable airborne bacteria with and without the control in operation. Results for a single, 15 W germicidal lamp showed reductions of 50% for Bacillus subtilis (B. subtilis) and Micrococcus luteus (M. luteus); tests with Escherichia coli (E. coli) showed nearly 100% reduction (E. coli were isolated only from the sampler nearest the aerosol source when the lamp was operating). The addition of louvers to a lamp greatly reduced its efficacy. Decay experiments showed that roughly 4-6 equivalent air changes per hour were achieved for B. subtilis with one or two lamps operating. These preliminary experiments demonstrated that this methodology was well suited for these evaluations and identified factors that could be modified to refine the study design for future work.
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Background: On April 15 and April 17, 2009, novel swine-origin influenza A (H1N1) virus (S-OIV) was identified in specimens obtained from two epidemiologically unlinked patients in the United States. The same strain of the virus was identified in Mexico, Canada, and elsewhere. We describe 642 confirmed cases of human S-OIV infection identified from the rapidly evolving U.S. outbreak. Methods: Enhanced surveillance was implemented in the United States for human infection with influenza A viruses that could not be subtyped. Specimens were sent to the Centers for Disease Control and Prevention for real-time reverse-transcriptase-polymerase-chain-reaction confirmatory testing for S-OIV. Results: From April 15 through May 5, a total of 642 confirmed cases of S-OIV infection were identified in 41 states. The ages of patients ranged from 3 months to 81 years; 60% of patients were 18 years of age or younger. Of patients with available data, 18% had recently traveled to Mexico, and 16% were identified from school outbreaks of S-OIV infection. The most common presenting symptoms were fever (94% of patients), cough (92%), and sore throat (66%); 25% of patients had diarrhea, and 25% had vomiting. Of the 399 patients for whom hospitalization status was known, 36 (9%) required hospitalization. Of 22 hospitalized patients with available data, 12 had characteristics that conferred an increased risk of severe seasonal influenza, 11 had pneumonia, 8 required admission to an intensive care unit, 4 had respiratory failure, and 2 died. The S-OIV was determined to have a unique genome composition that had not been identified previously. Conclusions: A novel swine-origin influenza A virus was identified as the cause of outbreaks of febrile respiratory infection ranging from self-limited to severe illness. It is likely that the number of confirmed cases underestimates the number of cases that have occurred.
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Recent studies suggest that humans exhale fine particles during tidal breathing but little is known of their composition, particularly during infection. We conducted a study of influenza infected patients to characterize influenza virus and particle concentrations in their exhaled breath. Patients presenting with influenza-like-illness, confirmed influenza A or B virus by rapid test, and onset within 3 days were recruited at three clinics in Hong Kong, China. We collected exhaled breath from each subject onto Teflon filters and measured exhaled particle concentrations using an optical particle counter. Filters were analyzed for influenza A and B viruses by quantitative polymerase chain reaction (qPCR). Twelve out of thirteen rapid test positive patients provided exhaled breath filter samples (7 subjects infected with influenza B virus and 5 subjects infected with influenza A virus). We detected influenza virus RNA in the exhaled breath of 4 (33%) subjects--three (60%) of the five patients infected with influenza A virus and one (14%) of the seven infected with influenza B virus. Exhaled influenza virus RNA generation rates ranged from <3.2 to 20 influenza virus RNA particles per minute. Over 87% of particles exhaled were under 1 microm in diameter. These findings regarding influenza virus RNA suggest that influenza virus may be contained in fine particles generated during tidal breathing, and add to the body of literature suggesting that fine particle aerosols may play a role in influenza transmission.
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More than a year after an influenza pandemic was declared in June 2009, the World Health Organization declared the pandemic to be over. Evaluations of the pandemic response are beginning to appear in the public domain. We argue that, despite the enormous effort made to control the pandemic, it is now time to acknowledge that many of the population-based public health interventions may not have been well considered. Prior to the pandemic, there was limited scientific evidence to support border control measures. In particular no border screening measures would have detected prodromal or asymptomatic infections, and asymptomatic infections with pandemic influenza were common. School closures, when they were partial or of short duration, would not have interrupted spread of the virus in school-aged children, the group with the highest rate of infection worldwide. In most countries where they were available, neuraminidase inhibitors were not distributed quickly enough to have had an effect at the population level, although they will have benefited individuals, and prophylaxis within closed communities will have been effective. A pandemic specific vaccine will have protected the people who received it, although in most countries only a small minority was vaccinated, and often a small minority of those most at risk. The pandemic vaccine was generally not available early enough to have influenced the shape of the first pandemic wave and it is likely that any future pandemic vaccine manufactured using current technology will also be available too late, at least in one hemisphere. Border screening, school closure, widespread anti-viral prophylaxis and a pandemic-specific vaccine were unlikely to have been effective during a pandemic which was less severe than anticipated in the pandemic plans of many countries. These were cornerstones of the population-based public health response. Similar responses would be even less likely to be effective in a more severe pandemic. We agree with the recommendation from the World Health Organisation that pandemic preparedness plans need review.
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Influenza is thought to be communicated from person to person by multiple pathways. However, the relative importance of different routes of influenza transmission is unclear. To better understand the potential for the airborne spread of influenza, we measured the amount and size of aerosol particles containing influenza virus that were produced by coughing. Subjects were recruited from patients presenting at a student health clinic with influenza-like symptoms. Nasopharyngeal swabs were collected from the volunteers and they were asked to cough three times into a spirometer. After each cough, the cough-generated aerosol was collected using a NIOSH two-stage bioaerosol cyclone sampler or an SKC BioSampler. The amount of influenza viral RNA contained in the samplers was analyzed using quantitative real-time reverse-transcription PCR (qPCR) targeting the matrix gene M1. For half of the subjects, viral plaque assays were performed on the nasopharyngeal swabs and cough aerosol samples to determine if viable virus was present. Fifty-eight subjects were tested, of whom 47 were positive for influenza virus by qPCR. Influenza viral RNA was detected in coughs from 38 of these subjects (81%). Thirty-five percent of the influenza RNA was contained in particles>4 µm in aerodynamic diameter, while 23% was in particles 1 to 4 µm and 42% in particles<1 µm. Viable influenza virus was detected in the cough aerosols from 2 of 21 subjects with influenza. These results show that coughing by influenza patients emits aerosol particles containing influenza virus and that much of the viral RNA is contained within particles in the respirable size range. The results support the idea that the airborne route may be a pathway for influenza transmission, especially in the immediate vicinity of an influenza patient. Further research is needed on the viability of airborne influenza viruses and the risk of transmission.
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Background: Institutional tuberculosis (TB) transmission is an important public health problem highlighted by the HIV/AIDS pandemic and the emergence of multidrug- and extensively drug-resistant TB. Effective TB infection control measures are urgently needed. We evaluated the efficacy of upper-room ultraviolet (UV) lights and negative air ionization for preventing airborne TB transmission using a guinea pig air-sampling model to measure the TB infectiousness of ward air. Methods and findings: For 535 consecutive days, exhaust air from an HIV-TB ward in Lima, Perú, was passed through three guinea pig air-sampling enclosures each housing approximately 150 guinea pigs, using a 2-d cycle. On UV-off days, ward air passed in parallel through a control animal enclosure and a similar enclosure containing negative ionizers. On UV-on days, UV lights and mixing fans were turned on in the ward, and a third animal enclosure alone received ward air. TB infection in guinea pigs was defined by monthly tuberculin skin tests. All guinea pigs underwent autopsy to test for TB disease, defined by characteristic autopsy changes or by the culture of Mycobacterium tuberculosis from organs. 35% (106/304) of guinea pigs in the control group developed TB infection, and this was reduced to 14% (43/303) by ionizers, and to 9.5% (29/307) by UV lights (both p < 0.0001 compared with the control group). TB disease was confirmed in 8.6% (26/304) of control group animals, and this was reduced to 4.3% (13/303) by ionizers, and to 3.6% (11/307) by UV lights (both p < 0.03 compared with the control group). Time-to-event analysis demonstrated that TB infection was prevented by ionizers (log-rank 27; p < 0.0001) and by UV lights (log-rank 46; p < 0.0001). Time-to-event analysis also demonstrated that TB disease was prevented by ionizers (log-rank 3.7; p = 0.055) and by UV lights (log-rank 5.4; p = 0.02). An alternative analysis using an airborne infection model demonstrated that ionizers prevented 60% of TB infection and 51% of TB disease, and that UV lights prevented 70% of TB infection and 54% of TB disease. In all analysis strategies, UV lights tended to be more protective than ionizers. Conclusions: Upper-room UV lights and negative air ionization each prevented most airborne TB transmission detectable by guinea pig air sampling. Provided there is adequate mixing of room air, upper-room UV light is an effective, low-cost intervention for use in TB infection control in high-risk clinical settings.
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Considerable controversy exists with regard to whether influenza virus and respiratory syncytial virus (RSV) are spread by the inhalation of infectious airborne particles and about the importance of this route, compared with droplet or contact transmission. Airborne particles were collected in an urgent care clinic with use of stationary and personal aerosol samplers. The amounts of airborne influenza A, influenza B, and RSV RNA were determined using real-time quantitative polymerase chain reaction. Health care workers and patients participating in the study were tested for influenza. Seventeen percent of the stationary samplers contained influenza A RNA, 1% contained influenza B RNA, and 32% contained RSV RNA. Nineteen percent of the personal samplers contained influenza A RNA, none contained influenza B RNA, and 38% contained RSV RNA. The number of samplers containing influenza RNA correlated well with the number and location of patients with influenza (r= 0.77). Forty-two percent of the influenza A RNA was in particles < or = 4.1 microm in aerodynamic diameter, and 9% of the RSV RNA was in particles < or = 4.1 microm. Airborne particles containing influenza and RSV RNA were detected throughout a health care facility. The particles were small enough to remain airborne for an extended time and to be inhaled deeply into the respiratory tract. These results support the possibility that influenza and RSV can be transmitted by the airborne route and suggest that further investigation of the potential of these particles to transmit infection is warranted.
Aerosolized viruses were passed through a high-intensity ultraviolet (UV) cell. This cell consisted of a long cylindrical aluminum tube [diameter, 7 in. (17.7 cm); length, 36 in. (91.4 cm)] with a highly reflective inner surface and a longitudinally extending helical baffle system which directed airborne particles in close proximity to a centrally located UV lamp. After having been passed through the UV cell, viral aerosols were collected with an Andersen sampler, and viral concentrations were determined by plaque assay methods on tissue cultures. Inactivation rates of greater than 99.9% were obtained for Coxsackie, influenza, Sindbis, and vaccinia viruses, and slightly less for adenovirus (96.8%), when the aerosols passed through the UV cell at 100 ft³/min. At aerosol flow rates of 200 ft³/min, inactivation rates were slightly lower; 91.3 for adenovirus, 97.5 and 96.7 for Coxsackie and Sindbis, respectively, and greater than 99.9% for influenza and vaccinia viruses.
A comprehensive treatment of the mathematical basis for modeling the disinfection process for air using ultraviolet germicidal irradiation (UVGI). A complete mathematical description of the survival curve is developed that incorporates both a two stage inactivation curve and a shoulder. A methodology for the evaluation of the three-dimensional intensity fields around UV lamps and within reflective enclosures is summarized that will enable determination of the UV dose absorbed by aerosolized microbes. The results of past UVGI studies on airborne pathogens are tabulated. The airborne rate constant for Bacillus subtilis is confirmed based on results of an independent test. A re-evaluation of data from several previous studies demonstrates the application of the shoulder and two-stage models. The methods presented here will enable accurate interpretation of experimental results involving aerosolized microorganisms exposed to UVGI and associated relative humidity effects