Toward Standardized Aerovirology: A Critical Review of Existing Results and Methodologies

Understanding the airborne survival
of viruses is important for
public health and epidemiological modeling and potentially to develop
mitigation strategies to minimize the transmission of airborne pathogens.
Laboratory experiments typically involve investigating the effects
of environmental parameters on the viability or infectivity of a
target airborne virus. However, conflicting results among studies
are common. Herein, the results of 34 aerovirology studies were compared
to identify links between environmental and compositional effects
on the viability of airborne viruses. While the specific experimental
apparatus was not a factor in variability between reported results,
it was determined that the experimental procedure was a major factor
that contributed to discrepancies in results. The most significant
contributor to variability between studies was poorly defined initial
viable virus concentration in the aerosol phase, causing many studies
to not measure the rapid inactivation, which occurs quickly after
particle generation, leading to conflicting results. Consistently,
studies that measured their reference airborne viability minutes after
aerosolization reported higher viability at subsequent times, which
indicates that there is an initial loss of viability which is not
captured in these studies. The composition of the particles which
carry the viruses was also found to be important in the viability
of airborne viruses; however, the mechanisms for this effect are unknown.
Temperature was found to be important for aerosol-phase viability,
but there is a lack of experiments that directly compare the effects
of temperature in the aerosol phase and the bulk phase. There is a
need for repeated measurements between different research groups under
identical conditions both to assess the degree of variability between
studies and also to attempt to better understand already published
data. Lack of experimental standardization has hindered the ability
to quantify the differences between studies, for which we provide
recommendations for future studies. These recommendations are as follows:
measuring the reference airborne viability using the “direct
method”; use equipment which maximizes time resolution; quantify
all losses appropriately; perform, at least, a 5- and 10-min sample,
if possible; report clearly the composition of the virus suspension;
measure the composition of the gas throughout the experiment. Implementing
these recommendations will address the most significant oversights
in the existing literature and produce data which can more easily
be quantitatively compared.