How to Interpret Environmental Dust Testing in CIRS Beyond the Score
Introduction
Environmental dust testing can provide valuable information when investigating a living environment in the context of CIRS. But a score or index rarely tells the whole story, and interpreting the findings requires looking at the bigger picture.
The most useful way to approach these reports is to treat them as an entry point into an investigation. Species, levels of elevation, reference values, building history, and the surrounding environment all contribute to understanding what the results may mean. The goal is not simply to decide whether a number is “good” or “bad,” but to understand what the findings may be telling you about the environment.
Start With the Species, Not Just the Score
Environmental reports contain a large amount of information, and it can be tempting to focus on the overall score or index.
The species-level information provides a more specific starting point. Organisms have distinct environmental preferences and implications. An elevated organism that is strongly associated with moisture or water intrusion may warrant a different investigation from an organism that is commonly found in soil, dust, or human skin.
This is why two homes with similar overall scores can require very different interpretations.
The key question is not simply, “How high is the score?” but “What organisms are contributing to this result?”
Understanding Asterisks and Fold Elevations
Different environmental dust testing reports may present results in different ways. The following example uses the EnviroBiomics reporting system to show how asterisks and fold elevations can indicate how elevated an individual species is relative to its reference level.
In the reporting system used in this example:
No asterisk indicates that the organism is not detected or is present at a very low level.
One asterisk represents approximately a five-fold elevation.
Two asterisks represent approximately a 50-fold elevation.
Three asterisks represent approximately a 500-fold elevation.
Two or three asterisks can provide an initial indication of species that warrant closer attention. However, the number of asterisks should always be interpreted alongside the identity of the organism and the context of the building. The same level of elevation does not necessarily have the same significance for every organism.
For example, Stachybotrys is a type of mold strongly associated with water intrusion. Even a relatively low level of elevation may therefore warrant closer investigation for possible moisture or water-damage issues. By contrast, the same level of elevation in an organism commonly associated with soil, outdoor environments, or normal human shedding may lead to a different line of investigation.
What Do Quartiles Tell You?
Quartiles provide another way of putting a result into context.
Rather than describing how elevated an individual species is, a quartile shows where a result sits within other US homes.
In simple terms, the reference population is divided into four sections, each representing 25% of the results. Q1 contains the lowest quarter, while Q4 contains the highest quarter.
This can provide useful context, but a high quartile does not automatically indicate a problem. A result in Q4 simply means that it falls within the highest quarter of the reference distribution.
The quartile should therefore be considered alongside the species present, the degree of elevation, and the wider building context.
In other words, Q4 is not a verdict on the building.
When the Numbers Do Not Agree
The different measures in an environmental dust report can sometimes appear to tell different stories. This is because they are describing different aspects of the result.
For example, a result may fall into a relatively high quartile without showing a substantial fold/asterisk elevation for an individual species. Conversely, individual species may show notable elevations even when the overall score or index is not particularly high.
When this happens, look more closely at what is actually contributing to the result.
Start with the individual species. What organism is present, and what is it associated with? Is it associated with moisture or water intrusion? Is it commonly found in soil or outdoor environments? Is it associated with human skin?
Then consider the level of elevation. The fold elevation or asterisk provides information about how elevated that individual species is relative to its reference level.
An overall score or index provides another layer of information. It can summarise multiple findings, but it does not necessarily show which individual organisms are contributing to the result.
The practical approach is therefore to read the different parts of the report together:
Quartile → Where does the result sit compared with the reference population?
Species → What organism is present, and what is it associated with?
Fold elevation/asterisk → How elevated is that organism?
Building context → Does the finding make sense given the history and environment?
This provides a more meaningful interpretation than relying on any single number.
Looking Beyond Species-Level Findings
The same approach can be applied to other types of environmental findings that do not identify a specific organism. Endotoxin testing is one example. Unlike species-level testing, it measures a bacterial component rather than identifying a particular organism.
Where Do Environmental Endotoxins Come From?
Endotoxins are components of the outer membrane of Gram-negative bacteria. These bacteria are widespread in soil, water, plants, animals, and other environments, so endotoxin can enter indoor dust from a variety of sources.
Potential sources include wastewater and sewage, animal or human waste, pets, outdoor soil, agricultural environments, flooding, and other sources of organic dust.
An endotoxin result does not, by itself, identify which bacteria produced it or where the endotoxin came from. The bacteria themselves can be investigated separately using microbiological or molecular testing, but finding Gram-negative bacteria in the same sample would not necessarily establish that they are responsible for the endotoxin result.
For this reason, the investigation needs to consider the building and its surroundings. Potential indoor sources include:
Plumbing leaks
Wastewater problems
Sewer gas or drain issues
Previous plumbing problems
Pets, litter boxes, or animal waste
If an obvious indoor source cannot be identified, the surrounding environment can also be considered. Nearby wastewater treatment facilities, livestock operations, flooding, septic systems, sewer problems, agricultural activity, and certain irrigation practices may provide additional context.
An indoor-to-outdoor comparison can also help interpret the finding. If endotoxin levels are substantially higher indoors than outdoors, this may provide a clue that an indoor source warrants closer investigation. If the outdoor result is substantially higher than the indoor result, the surrounding environment may be contributing more strongly to the finding. Similar indoor and outdoor levels would provide a different context again.
From Test Result to Investigation
Environmental testing is most useful when it changes the questions you ask.
A result can prompt you to investigate the building's history, inspect plumbing, examine nearby environmental sources, compare indoor and outdoor samples, or look more closely at individual species.
The important distinction is between using testing to make an informed decision and using a single number as a final verdict. A dust test is a snapshot; context turns that snapshot into a picture.
Environmental assessment in CIRS is therefore rarely about finding one number that tells you everything you need to know about an environment. The more useful approach is to combine the available information: species, levels of elevation, reference values, building history, and environmental surroundings.
The purpose of testing is not simply to collect more numbers. It is to understand what those numbers may be pointing toward—and then investigate accordingly.
