A New Filter Cassette for the Direct Microscopic Examination of Airborne Fungal Spores

Figures & data

FIG. 1 Arrangement of the six sample ports in the test section of the settling chamber, with alternating AOC and BA cassettes attached.

FIG. 2 Side view of the BA filter cassette showing one of the 3-mm square sample inlets.

FIG. 3 Interior of the BA cassette cowl showing the positions of the duplicate sample traces.

TABLE 1 The average spore concentrations (spores/m³) and variability per injection of the alcohol spore suspension into the chamber. The data are for multiple series of 6, 12, 15, and 20 injections

Concentration	Penicillium	Stachybotrys
Minimum	500	30
Maximum	800	50
Average	670	40
CV	20%	26%

TABLE 2 Variability of P. chrysogenum spore concentrations between the six sampling ports in the settling chamber for a single 10-minute test

Sampling Port	P. chrysogenum (spores/m^3)
1	10,600
2	9,950
3	10,350
4	9,9507
5	12,400
6	11,450
CV	9%

FIG. 4 The corner of a typical BA sample trace at 100× magnification. The sample trace was well defined and the 1.7 mm × 5.5 mm area did not vary between samples.

FIG. 5 The corner of a typical AOC sample trace at 100× magnification. The edges of the sample trace were diffuse and the 2 mm × 14.5 mm area often varied between samples.

TABLE 3 The CV between microscopic traverses for six representative sample traces with various spore densities. An average of 11 traverses for AOC samples and 10 traverses for BA samples

Air-o-Cell Cassette		BI-air Cassette
Spores/FOV	CV (%)	Spores/FOV	CV (%)
18	32	14	29
24	28	14	27
35	31	15	33
37	36	20	24
48	20	24	28
48	28	38	20

TABLE 4 Effect of filter pore size on collection efficiency for Penicillium and Stachybotrys Spores

	3 um Penicillium			Stachybotrys
Parameters Pore size	1.2 um	3 um	5 um	1.2 um	3 um	5 um
Avg Conc	10,512	10,625	8,539	518	712	485
CV	9 %	13 %	21 %	20 %	29 %	52 %
% of 1.2 um	100 %	101 %	81 %	100 %	137 %	94 %

TABLE 5 Effect of airflow rate on spore retention for the Bi-Air cassette. Average Penicillium concentrations (spores/m³) for 30-minute tests at airflow rates of 1, 2 and 3 lpm

Airflow rate	Air-O-Cell	Bi-Air	Ratio
1	1,673	3,677	2.2
1	16,937	30,631	1.8
2	3,819	9,308	2.4
2	20,304	25,079	1.2
3	6,036	12,083	2.0
3	17,132	24,331	1.4