Guidance for Interpretation of Mold Culture Results
There are no government-issued numerical standards for mold culture interpretation. However, some environmental companies, industrial hygienists, and other IAQ professionals use the following arbitrary numbers for guidance in interpreting microbial survey results.
The final mold interpretation should not be based solely on numbers! Information gathered from the walk-through investigation of the area is very significant, including sources of moisture or high humidity, and signs of visible mold growth. In air samples, it is important to consider the type and concentration of fungi indoors, as compared to outdoors or a non-complaint area. One should consider the indoor: outdoor fungal count ratio, the presence/absence of certain fungi indoors versus outdoors, the genus/species of predominant fungi indoors versus outdoors, and whether the fungi detected indoors are allergenic and/or toxigenic.
| Bioaerosol | ||
| <250 | CFU/m3 | Low/Normal |
| 250-1,000 | CFU/m3 | Moderate/Borderline |
| >1,000 | CFU/m3 | Active Growth/Sporulation |
| >5,000 | CFU/m3 | Very Active Growth/Sporulation |
| Swab/Wipe | ||
| <100 | CFU/in2 | No Growth/Background |
| <10,000 | CFU/in2 | Low/Normal Growth |
| 10,000-100,000 | CFU/in2 | Moderate Growth |
| 100,000-1,000,000 | CFU/in2 | Active Growth/Sporulation |
| >1,000,000 | CFU/in2 | Very Active Growth/Sporulation |
| Bulk substrate | ||
| <100 | CFU/g | No Growth |
| <25,000 | CFU/g | Low/Normal Growth |
| 25,000-200,000 | CFU/g | Moderate Growth |
| 200,000-1,000,000 | CFU/g | Active Growth/Sporulation |
| >1,000,000 | CFU/g | Very Active Growth/Sporulation |
| Micro-vac Dust | ||
| <5,000 | CFU/ft2 | Low/Normal |
| 5,000-25,000 | CFU/ft2 | Moderate/Borderline |
| 25,000-75,000 | CFU/ft2 | Active Growth/Sporulation |
| >75,000 | CFU/ft2 | Very Active Growth/Sporulation |
| Definitions | ||
| CFU = Colony Forming Unit | ||
| Colony = A mass of branching hyphae with or without spores, generally of one species and potentially started from one spore, cell, or propagule. | ||
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