Comparison of samplers collecting airborne influenza viruses: 1. Primarily impingers and cyclones

Abstract

Researchers must be able to measure concentrations, sizes, and infectivity of virus-containing particles in animal agriculture facilities to know how far infectious virus-containing particles may travel through air, where they may deposit in the human or animal respiratory tract, and the most effective ways to limit exposures to them. The objective of this study was to evaluate a variety of impinger and cyclone aerosol or bioaerosol samplers to determine approaches most suitable for detecting and measuring concentrations of virus-containing particles in air. Six impinger/cyclone air samplers, a filter-based sampler, and a cascade impactor were used in separate tests to collect artificially generated aerosols of MS2 bacteriophage and swine and avian influenza viruses. Quantification of infectious MS2 coliphage was carried out using a double agar layer procedure. The influenza viruses were titrated in cell cultures to determine quantities of infectious virus. Viral RNA was extracted and used for quantitative real time RT-PCR, to provide total virus concentrations for all three viruses. The amounts of virus recovered and the measured airborne virus concentrations were calculated and compared among the samplers. Not surprisingly, high flow rate samplers generally collected greater quantities of virus than low flow samplers. However, low flow rate samplers generally measured higher, and likely more accurate, airborne concentrations of Infectious virus and viral RNA than high flow samplers. To assess airborne viruses in the field, a two-sampler approach may work well. A suitable high flow sampler may provide low limits of detection to determine if any virus is present in the air. If virus is detected, a suitable lower flow sampler may measure airborne virus concentrations accurately.

Fig 1

(a) Ventilation air supply plenum with (b) nebulizer placed directly in front of the opening. (c) Sampling instruments arrayed in the isolation room.

Fig 2

Sampled infectious virus and viral RNA for air samplers as measured for (a) MS2 bacteriophage, (b) H3N2 swine influenza virus, and (c) H9N9 avian influenza virus. Bars represent geometric means and error bars represent ± one geometric standard deviation. Same letters indicate geometric means that are not significantly different from one another.

Fig 3

Infectious virus and viral RNA air concentrations measured by samplers for (a) MS2 bacteriophage, (b) H3N2 swine influenza virus, and (c) H9N9 avian influenza virus. Bars represent geometric means and error bars represent ± one geometric standard deviation. Same letters indicate geometric means that are not significantly different from one another.

Fig 4. Relative recovery measured for MS2 bacteriophage, H3N2 swine influenza virus, and H9N9 avian influenza virus for each of the air samplers.

Bars represent geometric means and error bars represent ± one geometric standard deviation. Same letters indicate geometric means that are not significantly different from one another within each type of virus.

Fig 5. Mean fractional size distributions normalized by the width of the size interval on a logarithmic scale for the size distribution by mass calculated from optical particle counter data and for live virus, viral RNA, and fluorescein sampled with the Andersen cascade impactor and the NIOSH Cyclone Bioaerosol Sampler during tests with MS2 bacteriophage.

Fig 6

Mean fractional size distributions normalized by the width of the size interval on a logarithmic scale for the size distribution by mass calculated from optical particle counter data and for viral RNA sampled with the Andersen cascade impactor and the NIOSH Cyclone Bioaerosol Sampler for (a) MS2 bacteriophage, (b) H3N2 swine influenza virus, and (c) H9N9 avian influenza virus. Bars represent ± one standard deviation from the mean value.