Overview
Alternaria is a genus of ubiquitous fungi with over 275 species, making it one of the most common mold genera worldwide. It is primarily an outdoor mold but regularly enters buildings through air infiltration. Research consistently identifies Alternaria as one of the most significant allergenic molds, particularly for patients with allergic rhinitis and asthma.
Alternaria spores are large (20-200 Ξm), club-shaped, and heavily pigmented â features that make them easy to identify microscopically but also mean they don’t remain airborne as long as smaller spores.
Key Point: Alternaria is ranked by the American Academy of Allergy, Asthma & Immunology as one of the most important allergenic molds. Sensitization to Alternaria is a recognized risk factor for asthma development and severe asthma exacerbations.
Common Species
Alternaria alternata
The most common and clinically significant species. A major outdoor allergen with well-documented associations with allergic rhinitis, allergic asthma, and severe asthma exacerbations.
Alternaria tenuissima
Commonly found on plant leaves, fruits, and vegetables. May be encountered on food products. Cross-reactive with A. alternata allergens.
Where It’s Found
Primary Outdoor Habitats
- Decaying plant material (leaves, stems, compost)
- Soil surfaces, especially cultivated areas
- Grasses and agricultural crops
- Rotting wood and tree bark
Indoor Locations
- Window sills and frames â condensation areas
- Bathroom surfaces, shower curtains
- Houseplants and soil
- HVAC systems â brought in from outdoor air
Seasonal Patterns
| Season | Level | Notes |
|---|---|---|
| Late Summer – Fall | Peak | August-October highest |
| Spring | Moderate | Rising counts |
| Winter | Low | Minimal outdoor counts |
Health Effects
Allergic Rhinitis
Alternaria is a major cause of seasonal allergic rhinitis. Sensitization prevalence ranges from 3-30% of patients with allergic respiratory disease. Symptoms include sneezing, runny nose, itchy eyes.
Asthma Connection
- Asthma development: Sensitization in childhood increases risk
- Severe asthma: Correlates with more severe phenotypes
- ER visits: High outdoor counts linked to asthma emergencies
- Fatal asthma: Research links exposure to fatal/near-fatal episodes
Alternaria in Oklahoma
Peak Season: August-October
Outdoor counts peak during late summer/early fall, coinciding with crop harvest and declining vegetation.
Agricultural Influence
Oklahoma’s extensive agricultural areas (wheat, cotton, hay) contribute to high regional counts.
Citations
- Bush RK, Prochnau JJ. “Alternaria-induced asthma.” JACI 2004.
- O’Hollaren MT, et al. “Exposure to an aeroallergen as a possible precipitating factor in respiratory arrest in young patients with asthma.” NEJM 1991.
- AAAAI. “Outdoor Allergens.” AAAAI.org.
- AAFA. “Mold Allergies.” AAFA.org, 2024.
- CDC. “Mold: Basic Facts.” CDC.gov, 2024.