About Aspergillus flavus/oryzae
Aspergillus flavus is best known as the source of aflatoxins, classified by IARC as Group 1 human carcinogens. That IARC classification is based primarily on dietary exposure (contaminated grains, peanuts, and corn); the indoor inhalation route is a different risk profile, and indoor concentrations relevant to human health aren't as well characterized. Indoors, A. flavus is found in damp HVAC systems, on damp walls and wallpaper, in house dust, and on bird droppings. It's also the second most common cause of invasive aspergillosis in immunocompromised patients. Whether any elevation here is clinically meaningful for any specific person (particularly anyone with liver conditions or compromised immune function) is a question for a qualified clinician.
Ecology and water requirements
Aspergillus flavus/oryzae is classified as a primary colonizer with xerophilic adaptations: capable of germinating and growing at water activity as low as Aw 0.78[2], well below what most molds tolerate. Primary colonizers establish first in damp or even mildly humid environments, often before any visible moisture problem is apparent. Elevated Aspergillus flavus/oryzae on an ERMI test is more often associated with long-term high humidity than with a sudden water event[3]. Common contexts include poorly ventilated areas, conditioned-vs-unconditioned boundary zones (attics, crawl spaces, unfinished basements), and dusty environments where ambient relative humidity is sufficient to support growth on settled organic material.
Mycotoxin biology
Aspergillus flavus/oryzae produces a range of secondary metabolites with biological activity. The compounds documented in the literature for this species are listed in the chips below. Mycotoxin production is not uniform across all strains and is influenced by substrate, temperature, and water activity[4]. The same isolate may produce substantially different metabolite profiles on drywall paper versus wood versus settled dust[5]. DNA-based detection via the ERMI panel identifies species presence but does not directly measure mycotoxin presence; detection of a mycotoxin-producing species in household dust does not establish exposure to that mycotoxin at any specific concentration.
Detection in dust versus visual inspection
DNA-based detection of Aspergillus flavus/oryzae in settled household dust (the basis of the ERMI panel[1]) integrates spore material from current and recent growth in the home, capturing exposure history over weeks to months. A positive detection in dust does not necessarily indicate currently-active growth at the time of sampling; conversely, an active growth site can produce relatively low dust spore counts if the spores are not being aerosolized (sealed wall cavities, behind vapor barriers, or under flooring). Interpretation requires considering the dust signal alongside building inspection, occupant symptom history, and the broader pattern of species detected on the panel.
Where it’s typically found
Aspergillus flavus/oryzae is documented on the following substrates and locations:
- Damp walls
- HVAC systems
- house dust
- bird droppings
- leather
- tarred wood flooring
- humidifiers
Mycotoxins
Compounds documented as produced by Aspergillus flavus/oryzae (presence and quantity vary by chemotype, strain, and substrate):
Mycotoxin production is not uniform across all strains and is influenced by substrate, temperature, and water activity. Detection of a mycotoxin-producing species in household dust does not directly establish exposure to that mycotoxin at any specific concentration.
On your ERMI report
Aspergillus flavus/oryzae is one of the 26 EPA water-damage indicator species used to compute the SLG1 component of the ERMI score (sometimes labeled "Group 1" in EPA documentation). Whether the level detected in any specific home is concerning depends on the broader pattern: which other species are elevated, the water-activity profile of the elevated species, the home's climate context, and (where relevant) the occupant's sensitivity history. Our interpretation report puts Aspergillus flavus/oryzae in that broader pattern.
Mycotoxins and extended panels
Related reference pages: the mycotoxins Aspergillus flavus/oryzae can produce, and the extended-panel species most closely related to it:
Related species
References
- Vesper SJ, McKinstry C, Haugland RA, et al. Development of an Environmental Relative Moldiness Index for U.S. homes. J Occup Environ Med. 2007;49(8):829–833.
- Pitt JI, Hocking AD. Fungi and Food Spoilage. 3rd ed. New York: Springer; 2009.
- World Health Organization. WHO Guidelines for Indoor Air Quality: Dampness and Mould. Copenhagen: WHO Regional Office for Europe; 2009.
- Nielsen KF. Mycotoxin production by indoor molds. Fungal Genet Biol. 2003;39(2):103–117.
- Miller JD, McMullin DR. Fungal secondary metabolites as harmful indoor air contaminants: 10 years on. Appl Microbiol Biotechnol. 2014;98(24):9953–9966.