Overview
Fusarium is a large genus of filamentous fungi with over 70 species, most of which are soil-dwelling plant pathogens with significant agricultural impact. In buildings, Fusarium indicates water damage and is commonly found on chronically wet materials, particularly carpeting and drywall after flooding.
Unlike ubiquitous outdoor molds like Cladosporium or Alternaria, finding Fusarium in indoor air at levels significantly above outdoor baselines typically indicates active indoor growth from water damage—it is not a normal component of indoor air.
Fusarium species are notable for their ability to produce potent mycotoxins, including trichothecenes and fumonisins. These toxins are a major concern in agricultural settings (food contamination) and are under research for potential health effects from indoor exposure.
Water Damage Indicator: Finding elevated Fusarium in indoor samples strongly suggests water intrusion or flooding. It requires sustained wetness to establish in buildings and is classified as a “secondary colonizer” — appearing after initial moisture events.
Common Species
Fusarium solani
Most common species in clinical settings. Can rarely cause keratitis (eye infections), especially in contact lens wearers. Also causes skin and nail infections in immunocompromised patients.
Fusarium oxysporum
A major plant pathogen commonly found in soils and on plants. Produces fusaric acid. Found in water-damaged buildings with soil contact or plant material.
Fusarium graminearum
Primary producer of deoxynivalenol (DON/vomitoxin) mycotoxin. Mainly an agricultural concern on wheat, barley, and corn. May enter buildings via contaminated grain products or plant debris.
Where It’s Found
Indoor Locations (Water Damage)
- Flooded carpeting and carpet padding — primary indoor substrate
- Water-damaged drywall and ceiling tiles
- Wet insulation materials
- Basement and crawl space surfaces with chronic moisture
- HVAC systems with condensation problems
- Houseplants and potting soil
Outdoor/Agricultural Sources
- Soil (natural habitat)
- Plant debris, especially grains and cereals
- Agricultural areas and crop fields
- Decaying vegetation
Growth Conditions
| Factor | Requirement | Notes |
|---|---|---|
| Moisture | High (aw > 0.90) | Requires wet conditions, not just humidity |
| Temperature | 25-30°C optimal | Some species tolerate cooler temps |
| Appearance | Pink, purple, red, or white | Distinctive coloration in some species |
| Classification | Secondary colonizer | Appears after initial water event, not immediately |
Health Effects
Mycotoxins
Fusarium species produce several mycotoxins of concern:
- Trichothecenes — Immunosuppressive and cytotoxic compounds
- Fumonisins — Associated with esophageal cancer risk (food contamination)
- Zearalenone — Estrogenic effects
Note: Most mycotoxin health effects are established through ingestion (contaminated food). Research on inhalation exposure from indoor mold is ongoing but less definitive.
Infections (Fusariosis)
Fusarium can cause opportunistic infections called fusariosis, primarily in immunocompromised patients:
- Keratitis — Eye infections, notably in contact lens wearers (2006 outbreak linked to lens solution)
- Onychomycosis — Nail infections
- Skin infections — Through wound contamination
- Disseminated infection — Rare, in severely immunocompromised patients
Allergic Reactions
Like most molds, Fusarium can trigger allergic reactions in sensitized individuals. Symptoms include respiratory irritation, sneezing, and nasal congestion.
Testing Significance
Finding Fusarium in indoor samples has specific diagnostic implications:
Water Damage Marker
Elevated indoor Fusarium strongly suggests past or current water intrusion. Unlike ubiquitous outdoor molds, it doesn’t enter buildings passively in significant quantities.
Carpet/Flooding History
When found on surface samples from carpeting, it often indicates the carpet experienced water damage that was not adequately remediated.
Fusarium in Oklahoma
Agricultural Presence
Oklahoma’s wheat, corn, and hay production means Fusarium is common in agricultural soils. Properties near farmland may have higher outdoor baseline levels.
Storm and Flood Damage
TrueSight frequently identifies Fusarium in Oklahoma homes with flood history, particularly on carpeting that was wet for extended periods after storms or plumbing failures.
Foundation Moisture
Oklahoma’s clay soils and foundation movement can cause water intrusion into basements and crawl spaces. Fusarium colonization in these areas indicates chronic moisture problems.
Citations
- CDC. “Mold: Basic Facts.” CDC.gov, 2024.
- WHO. “Guidelines for Indoor Air Quality: Dampness and Mould.” WHO, 2009.
- Chang DC, et al. “Multistate outbreak of Fusarium keratitis.” JAMA 2006.
- IICRC S520 Standard for Professional Mold Remediation.
- EPA. “Mold Remediation in Schools and Commercial Buildings.”