If a practitioner has mentioned MARCoNS, or you've run into the term researching mold illness and CIRS, the next question is usually practical: how do you actually find out whether it's present? The answer is a specific kind of nasal culture test. Here's how it works, step by step, and how to make sense of what comes back.
What the test actually is
MARCoNS testing is a deep nasal swab culture. A thin swab is used to collect a sample from well inside the nasal passage — deeper than a standard anterior-nares swab — and the sample is sent to a laboratory, where it's cultured to see what grows. Specialty labs used in the mold-illness community then identify any coagulase-negative staphylococci and run an antibiotic-sensitivity panel on them. If the staph recovered is resistant to two or more classes of antibiotics, it meets the working definition of MARCoNS — multiple antibiotic resistant coagulase-negative staphylococci. (New to the term? Start with our plain-language MARCoNS guide.)
How the sample is collected
Testing is typically ordered by a practitioner familiar with biotoxin illness, and home-collection kits exist as well: the kit ships with a swab and instructions, you (or ideally a steady-handed helper) collect the sample, and it goes back to the lab by mail. Collection matters more than people expect — the organisms of interest live deep in the nasal passages, so a shallow swab can miss them entirely. Labs also commonly report whether the recovered staph is a biofilm former, which is part of why these colonizations are described as persistent; our article on sinus biofilm disruptors explains that side of the picture.
Reading the results
A typical report tells you three things: whether coagulase-negative staph was recovered, what it's resistant to, and often whether it forms biofilm. A result that shows staph resistant to two-plus antibiotic classes is what practitioners call "MARCoNS positive." What to do with that finding is an individualized clinical conversation — approaches people discuss with their practitioners are covered in our overview of MARCoNS treatment options.
The limitations worth knowing
Like any culture, this is a snapshot. A single swab can miss organisms if collection is shallow, and results reflect one point in time — which is why practitioners often retest some weeks after completing a protocol rather than assuming the first result is the permanent truth. A negative result narrows possibilities; it doesn't always close the question. And a positive result is a finding to interpret with a professional, not a diagnosis you act on alone.
Where nasal hygiene fits
Separate from any testing or treatment decisions, many people in this community keep a simple daily nasal-care routine. A xylitol-based option such as our EDTA and xylitol nasal spray is formulated to help rinse, cleanse, and moisturize the nasal passages for comfortable everyday use. It is a hygiene product, not a treatment for any condition — and not a substitute for testing when you and your practitioner think testing is warranted.
This article is for general educational purposes only and is not medical advice. It is not intended to diagnose, treat, cure, or prevent any disease. Statements about nasal-care products have not been evaluated by the Food and Drug Administration. Talk with a qualified healthcare professional about testing and any treatment decisions.
