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

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Researchers from the University of Minnesota School of Public Health and College of Veterinary Medicine are publishing a series of articles in PLOS ONE comparing the various air samplers used to detect airborne viruses such as influenza. This first publication, available in open access, focuses on impingers and cyclones.

Highlights

  • Higher quantities of virus were recovered by high flow rate samplers
  • Lower flow rate samplers performed better when virus concentrations were high
  • Based on the question of interest, a different air sampler might be more efficient.

Methods

Live cultures of three different viruses -two influenza strains (avian and swine) and a coliphage serving as a model- were nebulized in front of the ventilation inlet such that the aerosol concentrations and size distributions were uniform. The suspensions were aerosolized at a rate of approximately 0.39 mL/min during the tests. Six different air samplers were run simultaneously for 30min to collect the aerosol particles. Samples were then tested by PCR and virus isolation to 1)estimate virus concentration and 2)assess its viability.

Results

None of the viruses were inactivated systematically by the nebulization process during the test period. Virus concentrations varied between strains used. The figure below shows the mean of the quantity of infectious virus and viral RNA collected by each of the air samplers for the swine influenza virus.

Figure 1. Sampled infectious virus and viral RNA for air samplers as measured for H3N2 swine influenza virus

Additionally, authors calculated the relative recovery rate of virus from the sample, representing the fraction of nebulized virus that remains infectious after sampling and analysis.

Figure 2. Relative recovery measured for MS2 bacteriophage, H3N2 swine influenza virus, and H9N9 avian influenza virus for each of the air samplers.

Visit the journal webpage to read the full article available in open access.

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.