Figure 2 and Table 3 show results from the
150-m3 microbial barrier test chamber aerosol challenge study. At four of the concentrations tested, the biological counts recovered
by the IMD-A instruments (IMD-A 1 and IMD-A 2) were equivalent. At all concentrations tested, the mean recoveries from the
AGI method were higher than recoveries observed from the IMD-A instruments and the Anderson air sampler. The microbial recoveries
from the Anderson air sampler varied when compared with the results from the IMD-A instruments and the AGI at each of the
four concentrations tested. We observed a high degree of correlation for microbial recoveries between the two IMD-A instruments
and between the IMD-A instruments and the AGI, as shown in Table 4. The degree of correlation between IMD-A and Anderson air
sampler and between the AGI and Anderson air sampler were substantially lower.
Microbial recoveries from environmental air in cleanroom environments Class E (ISO 9), Class D (ISO 8, Class 100,000 at operational
and static), and Class C (ISO 7/8, Class 10,000 at static and 100,000 at operational) are shown in Figures 3, 4, and 5 respectively.
In all three classified areas, the microbial recoveries from the SAS air sampler were lower than the biological counts recovered
by the IMD-A. Correlations (r2) between the IMD-A and the SAS air sampler for Class E, Class, D, and Class C were 0.51, 0.42, and 0.32, respectively. Of
the several replicated tests done in the Class A (ISO 5) environment, no biological counts were detected using either the
IMD-A or the SAS air sampler (data not shown).
We also assessed microbial recoveries from environmental air in an unclassified office space environment using the IMD-A and
AGI methods coupled with ScanRDI (Figure 6). Mean microbial recoveries from the environmental air were nearly identical between
IMD-A and AGI method coupled with ScanRDI.
THE FUTURE OF IMD-A MONITORING
Results for the controlled microbial barrier test chamber studies demonstrate that the microbial recoveries obtained from
the IMD-A units were comparable to or higher than the conventional culture based air sampling methods and indicate that the
IMD-A has the potential to reliably evaluate microbial populations in environmental air. Mean microbial recoveries from the
IMD-A were slightly lower than, but in the same order of magnitude as, those recovered by the AGI. On the other hand, microbial
recoveries from the Anderson air sampling method were substantially lower than those recovered using the IMD-A or the AGI
The strong correlation (Table 4) in microbial recoveries between the IMD-A and the AGI suggests that the IMD-A reliably detects
microbial populations in environmental air. This is further supported by the fact that the mean microbial recoveries from
environmental air were nearly identical between the IMD-A and the AGI method coupled with ScanRDI analysis (Figure 6). The
slightly higher microbial recoveries attained with the AGI method in the microbial barrier test chamber can be explained by
the fact that the impingement method is known to disperse microbial aggregates more effectively than other methods used to
sample environmental air, while the IMD-A would potentially undercount microbial aggregates.