Table 1. Comparison of impinger and PTFE filter efficiencies for culturable virus and viral RNA.

	Sample Source: impinger	Filter	Filter	Ratiod
Aerosol timea	FFU/collectionb	FFU/collectionc	GEq RNA/collection	FFU∶RNA
10 min	4.9 (0–19.6) E+03	4.9 (0.2–12.5) E+03	2.0 (0.9–3.9) E+06	1∶411
20 min	16.2 (0–28.5) E+03	12.2 (5.0–25.0) E+03	4.2 (2.3–7.6) E+06	1∶344
30 min	35.7 (19.5–49.3) E+03	4.0 (3.0–5.5) E+03	6.8 (4.1–9.1) E+06	1∶1705

^aVirus NC99 was nebulized in 6 experiments with impinger alone and 9 experiments with impinger and PTFE filter collections in parallel. The mean (range) total dose nebulized was 1.8 (1.1–2.2)×10⁷ FFU, calculated by virus concentration in Collison at beginning of aerosol generation times fluid volume nebulized for each run.

^bImpinger collection measured for 5.4 (range 5.3–5.5) L/min, reported as total FFU collected during interval of nebulization. N = 5 at each time point as one outlier value was removed from each group.

^cPTFE filter collection combines two filters in parallel for total flow of 4.0 L/min, reported as total FFU and total genome equivalents (GEq) of RNA measured by T5000 assay.

^dRatio of group means of FFU and GEq RNA collected respectively.