c Laboratory studies of virus aerosols have been criticized for generating airborne viruses from artificial nebulizer suspensions (e.g., cell culture media), which do not mimic the natural release of viruses (e.g., from human saliva). The objectives of this study were to determine the effect of human saliva on the infectivity and survival of airborne virus and to compare it with those of artificial saliva and cell culture medium. A stock of MS2 bacteriophage was diluted in one of three nebulizer suspensions, aerosolized, size selected (100 to 450 nm) using a differential mobility analyzer, and collected onto gelatin filters. Uranine was used as a particle tracer. The resulting particle size distribution was measured using a scanning mobility particle sizer. The amounts of infectious virus, total virus, and fluorescence in the collected samples were determined by infectivity assays, quantitative reverse transcription-PCR (RT-PCR), and spectrofluorometry, respectively. For all nebulizer suspensions, the virus content generally followed a particle volume distribution rather than a number distribution. The survival of airborne MS2 was independent of particle size but was strongly affected by the type of nebulizer suspension. Human saliva was found to be much less protective than cell culture medium (i.e., 3% tryptic soy broth) and artificial saliva. These results indicate the need for caution when extrapolating laboratory results, which often use artificial nebulizer suspensions. To better assess the risk of airborne transmission of viral diseases in real-life situations, the use of natural suspensions such as saliva or respiratory mucus is recommended.T he potential involvement of virus aerosols in the transmission of human respiratory diseases, although still under considerable debate, has led to increased public concern. Several studies have found that a variety of respiratory viruses, including influenza virus and severe acute respiratory syndrome (SARS) coronavirus, could be present at high concentrations in human saliva and respiratory mucus (1-3). When infected individuals cough, sneeze, speak, or simply breathe, particles of saliva and/or respiratory mucus that carry viruses can be easily generated (4, 5), resulting in an increased risk of viral infection by aerosols.In an effort to understand and control transmission of viral diseases via aerosols, researchers have generated airborne viruses in laboratories to study their infectivity and survival (i.e., the ability to remain infectious) since the 1930s. Laboratory-generated virus aerosols are commonly produced from liquid suspensions using pneumatic nebulizers such as Collison nebulizers, as the wet-dispersion technique simulates many dispersion processes of viruses in the natural environment (6). However, the composition of liquid suspensions from which virus aerosols are generated (also known as nebulizer suspensions) is known to affect the infectivity/survival of airborne viruses (7,8). Given that many laboratory studies use artificial nebulizer suspensi...
