Acidic pH inactivation of SARS-CoV-2 in exhaled breath and expectoration (ApHiCoV)

Acidic pH inactivation is known to be effective against enveloped viruses, such as SARS-CoV-2, which exposed to a low pH will denature spontaneously. Similar to pasteurization, viral reduction by chemical treatment at pH ~< 4, is thought to be achieved by destroying the lipid envelope, which results in an effective inactivation of the viruses. Several previous studies, e.g. for avian influenza virus and Bovine diarrhoea virus , suggest an exponential decay of active virus titer, exp(-t/t), with mean lifetimes t = 3-4 minutes upon exposure to pH = 4 (i.e. titer reductions by 99 % after less than 15 minutes). Similar investigations for SARS-CoV-2 are still lacking. ApHiCoV will investigate the possibility to use gaseous acetic acid (CH3COOH) in room air, as an easy-to-apply measure, in order to lower the pH of exhalation aerosol, expectorated droplets and contaminated contact sur-faces, and thereby to effectively mitigate the risk of transmission of enveloped viruses such as SARS-CoV-2. To this end we will- determine the thermodynamics of airway lining fluid and mucus and molecular diffusion processes therein, in particular with respect to solubility and diffusivity of CH3COOH;- investigate the uptake kinetics of CH3COOH into airway lining fluid and mucus of micron-sized aerosol particles, millimeter-sized droplets and contaminated planar contact surfaces;- consider the buffering by ammonium (NH4+ ), i.e. its neutralization by CH3COOH in the exhaled or expectorated substance as well as the loss of ammonia (NH3) to the gas phase of the indoor air;- determine the kinetics of pH-change (within milliseconds to minutes) inside the exhaled aerosol particles and expectorated drops subject to CH3COOH in the indoor air;- identify the target pH, i.e. the optimum acidity between being most efficient in virus inactivation, yet still acceptable for the health of the exposed individuals;- determine the pH-dependent inactivation kinetics of SARS-CoV-2 in the acidified airway lining fluid and mucus.These investigations will be performed experimentally in due consideration of biosafety and by thermodynamic and kinetic modelling. Experimental work will include the investigation of CH3COOH uptake kinetics of droplets in the 1-35 µm size regime by means of an electrodynamic balance, a direct determination of droplet pH for these droplets, and the measurement of active virus titer reduction in acidified airway lining fluid and mucus in a BSL-3 laboratory. Modeling work will apply a state-of-the-art thermodynamic and kinetic model applied in spherical and planar geometry for droplets and contaminated contact surfaces. We aim at answering the following questions:- Can rapid SARS-CoV-2 inactivation by pH-reduction be reached by applying indoor CH3COOH below the legal permissible exposure limit for 8-hour work-shifts, i.e. at concentrations below 10 ppmv?- Can such a pH-reduction even be reached by applying indoor CH3COOH below the odor threshold of unacclimatized individuals of ~1 ppmv? - If the results of this investigation are encouraging, could gaseous CH3COOH be used as disinfecting measure in hospitals?- Given CH3COOH application would be a cheap and easy-to-apply measure, allowing the inactivation of viruses in exhaled aerosol, in droplets and on all kinds of surfaces, could it potentially also be applied in other places in the public domain or in private houses?