Charbel Harb

Bio: Charbel Harb is an academic researcher from Virginia Tech. The author has contributed to research in topics: Environmental science & Sea spray. The author has an hindex of 3, co-authored 7 publications receiving 86 citations.

Inward and outward effectiveness of cloth masks, a surgical mask, and a face shield

Abstract: We evaluated the effectiveness of 11 face coverings for material filtration efficiency, inward protection efficiency on a manikin, and outward protection efficiency on a manikin. At the most penetr...

Increasing Freshwater Salinity Impacts Aerosolized Bacteria.

Abstract: Increases in the salt concentration of freshwater result in detrimental impacts on water quality and ecosystem biodiversity. Biodiversity effects include freshwater microbiota, as increasing salinity can induce shifts in the structure of native freshwater bacterial communities, which could disturb their role in mediating basal ecosystem services. Moreover, salinity affects the wave breaking and bubble-bursting mechanisms via which water-to-air dispersal of bacteria occurs. Given this dual effect of freshwater salinity on waterborne bacterial communities and their aerosolization mechanism, further effects on aerosolized bacterial diversity and abundance are anticipated. Cumulative salt additions in the freshwater-euhaline continuum (0-35 g/kg) were administered to a freshwater sample aerosolized inside a breaking wave analogue tank. Waterborne and corresponding airborne bacteria were sampled at each salinity treatment and later analyzed for diversity and abundance. Results demonstrated that the airborne bacterial community was significantly different (PERMANOVA; F1,22 = 155.1, r2 = 0.38, p < 0.001) from the waterborne community. The relative aerosolization factor (r-AF), defined as the air-to-water relative abundance ratio, revealed that different bacterial families exhibited either an enhanced (r-AF ≫ 1), neutral (r-AF ∼ 1), or diminished (r-AF ≪ 1) transfer to the aerosol phase throughout the salinization gradient. Going from freshwater to euhaline conditions, aerosolized bacterial abundance exhibited a nonmonotonic response with a maximum peak at lower oligohaline conditions (0.5-1 g/kg), a decline at higher oligohaline conditions (5 g/kg), and a moderate increase at polyhaline-euhaline conditions (15-35 g/kg). Our results demonstrate that increases in freshwater salinity are likely to influence the abundance and diversity of aerosolized bacteria. These shifts in aerosolized bacterial communities might have broader implications on public health by increasing exposure to airborne pathogens via inhalation. Impacts on regional climate, related to changes in biological ice-nucleating particles (INPs) emission from freshwater, are also expected.

A guideline to limit indoor airborne transmission of COVID-19.

Abstract: The current revival of the American economy is being predicated on social distancing, specifically the Six-Foot Rule, a guideline that offers little protection from pathogen-bearing aerosol droplets sufficiently small to be continuously mixed through an indoor space. The importance of airborne transmission of COVID-19 is now widely recognized. While tools for risk assessment have recently been developed, no safety guideline has been proposed to protect against it. We here build on models of airborne disease transmission in order to derive an indoor safety guideline that would impose an upper bound on the "cumulative exposure time," the product of the number of occupants and their time in an enclosed space. We demonstrate how this bound depends on the rates of ventilation and air filtration, dimensions of the room, breathing rate, respiratory activity and face mask use of its occupants, and infectiousness of the respiratory aerosols. By synthesizing available data from the best-characterized indoor spreading events with respiratory drop size distributions, we estimate an infectious dose on the order of 10 aerosol-borne virions. The new virus (severe acute respiratory syndrome coronavirus 2 [SARS-CoV-2]) is thus inferred to be an order of magnitude more infectious than its forerunner (SARS-CoV), consistent with the pandemic status achieved by COVID-19. Case studies are presented for classrooms and nursing homes, and a spreadsheet and online app are provided to facilitate use of our guideline. Implications for contact tracing and quarantining are considered, and appropriate caveats enumerated. Particular consideration is given to respiratory jets, which may substantially elevate risk when face masks are not worn.

Flow Physics of COVID-19

Abstract: Flow physics plays a key role in nearly every facet of the COVID-19 pandemic. This includes the generation and aerosolization of virus-laden respiratory droplets from a host, its airborne dispersion and deposition on surfaces, as well as the subsequent inhalation of these bioaerosols by unsuspecting recipients. Fluid dynamics is also key to preventative measures such as the use of face masks, hand-washing, ventilation of indoor environments, and even social distancing. This article summarizes what we know, and more importantly, what we need to learn about the science underlying these issues so that we are better prepared to tackle the next outbreak of COVID-19 or a similar disease.

Effectiveness of Face Mask or Respirator Use in Indoor Public Settings for Prevention of SARS-CoV-2 Infection — California, February–December 2021

Abstract: The use of face masks or respirators (N95/KN95) is recommended to reduce transmission of SARS-CoV-2, the virus that causes COVID-19 (1). Well-fitting face masks and respirators effectively filter virus-sized particles in laboratory conditions (2,3), though few studies have assessed their real-world effectiveness in preventing acquisition of SARS-CoV-2 infection (4). A test-negative design case-control study enrolled randomly selected California residents who had received a test result for SARS-CoV-2 during February 18-December 1, 2021. Face mask or respirator use was assessed among 652 case-participants (residents who had received positive test results for SARS-CoV-2) and 1,176 matched control-participants (residents who had received negative test results for SARS-CoV-2) who self-reported being in indoor public settings during the 2 weeks preceding testing and who reported no known contact with anyone with confirmed or suspected SARS-CoV-2 infection during this time. Always using a face mask or respirator in indoor public settings was associated with lower adjusted odds of a positive test result compared with never wearing a face mask or respirator in these settings (adjusted odds ratio [aOR] = 0.44; 95% CI = 0.24-0.82). Among 534 participants who specified the type of face covering they typically used, wearing N95/KN95 respirators (aOR = 0.17; 95% CI = 0.05-0.64) or surgical masks (aOR = 0.34; 95% CI = 0.13-0.90) was associated with significantly lower adjusted odds of a positive test result compared with not wearing any face mask or respirator. These findings reinforce that in addition to being up to date with recommended COVID-19 vaccinations, consistently wearing a face mask or respirator in indoor public settings reduces the risk of acquiring SARS-CoV-2 infection. Using a respirator offers the highest level of personal protection against acquiring infection, although it is most important to wear a mask or respirator that is comfortable and can be used consistently.