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Airborne virus sampling: Efficiencies of samplers and their detection limits for infectious bursal disease virus (IBDV).

INTRODUCTION
The airborne transmission of infectious diseases in livestock production is increasingly receiving research attention. Reliable techniques of air sampling are crucial to underpin the findings of such studies. This study evaluated the physical and biological efficiencies and detection limits of four samplers (Andersen 6-stage impactor, all-glass impinger "AGI-30", OMNI-3000 and MD8 with gelatin filter) for collecting aerosols of infectious bursal disease virus (IBDV).


MATERIALS AND METHOD
IBDV aerosols mixed with a physical tracer (uranine) were generated in an isolator, and then collected by the bioaerosol samplers. Samplers' physical and biological efficiencies were derived based on the tracer concentration and the virus/tracer ratio, respectively. Detection limits for the samplers were estimated with the obtained efficiency data.


RESULTS
Physical efficiencies of the AGI-30 (96%) and the MD8 (100%) were significantly higher than that of the OMNI-3000 (60%). Biological efficiency of the OMNI-3000 (23%) was significantly lower than 100% (P < 0.01), indicating inactivation of airborne virus during sampling. The AGI-30, the Andersen impactor and the MD8 did not significantly inactivate virus during sampling. The 2-min detection limits of the samplers on airborne IBDV were 4.1 log10 50% egg infective dose (EID50) m (-3) for the Andersen impactor, 3.3 log10 EID50 m (-3) for the AGI-30, 2.5 log10 EID50 m (-3) for the OMNI-3000, and 2.9 log10 EID50 m (-3) for the MD8. The mean half-life of IBDV aerosolized at 20 °C and 70% was 11.9 min.


CONCLUSION
Efficiencies of different samplers vary. Despite its relatively low sampling efficiency, the OMNI-3000 is suitable for use in environments with low viral concentrations because its high flow rate gives a low detection limit. With the 4 samplers investigated, negative air samples cannot guarantee virus-free aerial environments, which means that transmission of infectious agents between farms may still occur even when no virus has been detected.