Detection and Isolation of Airborne Influenza A H3N2 Virus Using a Sioutas Personal Cascade Impactor Sampler

Abstract

The air we breathe contains microorganisms that can cause infectious respiratory diseases. After two occupants of an apartment were diagnosed with influenza in February of 2013, efforts were made to detect and isolate airborne influenza virus using two different types of active air samplers: a Sioutas Personal Cascade Impactor Sampler (PCIS) and an SKC BioSampler. The PCIS collects size-fractionated particles by impaction on polytetrafluoroethylene filters, whereas the SKC BioSampler collects airborne particles in liquid media. Influenza H3N2 virus was collected by both types of air samplers. The PCIS collected a range of particle sizes containing influenza virus near one of the sick individuals but only ultrafine particles when the samplers were positioned farther away. Viable virus was present in the liquid collection media of the SKC BioSampler and some PCIS filters. These findings suggest that influenza patients produce ultrafine aerosol particles that contain viable virus.

Figure 1

Sioutas Personal Cascade Impactor Sampler (PCIS). (a) Schematic representation of the five interior sections of a PCIS. Each stage has an upper acceleration compartment and a lower impaction-collector surface. (b) Photograph of a PCIS unit. For size perspective, a coin is shown to the right of the PCIS.

Figure 2

Schematic layout of the apartment unit of this study (drawn to scale). Symbols used for the diagram are explained in the figure legend.

Figure 3

Early formation of influenza virus-specific CPE in cells inoculated with material collected by a PCIS at air sampling site 3. (a) Noninfected ATCC MDCK cells (negative control), 3 days postseed. (b) ATCC MDCK cells inoculated with material scraped off the PCIS after-filter. (c) Noninfected MDCK-SIAT2,6-UF cells, (negative control), 3 days postseed. (d) MDCK-SIAT2,6-UF cells inoculated with material scraped off the PCIS after-filter.

Figure 4

RT-PCR amplification of an influenza virus H3N2 subgenomic hemagglutinin gene sequence. Shown in an ethidium-bromide-stained 1.5% agarose gel loaded with a 100-bp ladder (lane marked “M”) and a 1,127 bp amplicon corresponding to the N-terminal half of the hemagglutinin gene sequence.