Most severe asthma attacks get blamed on the weather or a missed inhaler. In a group of young patients who actually stopped breathing, nearly every one was allergic to one common seasonal mold.
A severe asthma attack that ends in respiratory arrest, the point where breathing stops, is the outcome every asthma plan is built to prevent. A study from more than three decades ago found that a single seasonal mold sat behind a striking share of them in young patients. It is worth revisiting now, in August, because this is the mold’s peak season.
What the study found
Mark O’Hollaren, John Yunginger and colleagues at the Mayo Clinic studied 11 young asthma patients who had suffered a sudden respiratory arrest and published the results in the New England Journal of Medicine in 1991. Each patient was compared against matched asthma patients who had not arrested, and everyone was skin-tested for sensitivity to Alternaria alternata, one of the most common outdoor molds. Every arrest had happened in the upper Midwest, in summer or early fall.
Ten of the 11 respiratory-arrest patients (91%) tested positive for Alternaria allergy, against 31% of the comparison patients (P<0.001). Among the nine who had blood drawn, every one had elevated IgE antibodies to the mold. Adjusted for age, Alternaria sensitivity carried an odds ratio of 189.5 for respiratory arrest, with a wide 95% confidence interval from 6.5 to 5535.8 (O’Hollaren et al., 1991).
Read plainly: nearly every young patient who stopped breathing during an asthma attack was allergic to the same mold, and the attacks landed in that mold’s high season.
Why this mold, and why late summer
Alternaria is not a bathroom-tile mold. Its spores peak outdoors on warm, dry, breezy days in late summer and early fall, drift indoors through open windows and on clothing, and it also grows on damp indoor surfaces, houseplant soil, and food. In someone already sensitized, a sudden spike in exposure can set off fast, severe airway narrowing. The fact that the arrests clustered in the mold’s peak season is the pattern the authors flagged, and it is why a warm Pacific Northwest August and September are worth paying attention to if asthma runs in the house.
Does it hold up
Later reviews of Alternaria and asthma point the same direction. Sensitization to this mold is a recognized marker for severe and hard-to-control asthma, especially in children and young adults. The 1991 figures look dramatic because the outcome was so extreme, but the underlying link has been seen repeatedly since.
The limits, kept honest
This was a small, retrospective case-control study of just 11 arrest patients, which is exactly why the confidence interval is so enormous, from about 6.5 to over 5,500. The odds ratio of 189.5 is a very loud signal, not a precise risk figure. A positive skin test shows sensitization, not proof that Alternaria alone caused each arrest, and these were upper-Midwest patients, a region where outdoor Alternaria runs high. What survives all of that: nearly every young patient who stopped breathing was allergic to the same seasonal mold, and the events landed in that mold’s season.
What actually helps
If someone in your home has allergic asthma, it is worth knowing whether they are sensitized to Alternaria, which an allergist can test for, and worth being extra careful on high-spore days in late summer and fall. Keep indoor humidity under about 60%, run kitchen and bathroom exhaust fans, and fix leaks within a day or two so indoor mold never establishes. Remove visible growth and the damp material under it. Keep rescue medication within reach and an asthma action plan current through spore season.
Be clear-eyed about the shortcuts on the shelf. Ozone-generating “air purifiers” are sold as mold killers, yet the U.S. EPA warns that ozone is a lung irritant and these machines are not a safe or effective way to clean indoor air, which is the last thing you want near reactive airways. Fogging sprays and “mold bombs” coat a surface and leave the moisture that grew the mold, so it returns. Cheap “mold detector” gadgets mostly read general dust. None of them tell you whether a sensitized person is breathing a mold they react to.
A note on certainty: this is one small, retrospective study of 11 arrest patients, so the numbers are directional rather than precise, and an association is not proof that mold caused any one person’s arrest. What holds up: nearly every young patient who suffered a respiratory arrest was allergic to a single seasonal mold, and Alternaria keeps ranking as a marker for severe, hard-to-control asthma across the wider literature.
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Sources: O’Hollaren MT, Yunginger JW, Offord KP, Somers MJ, O’Connell EJ, Ballard DJ, Sachs MI. “Exposure to an aeroallergen as a possible precipitating factor in respiratory arrest in young patients with asthma.” New England Journal of Medicine 1991;324(6):359-363. U.S. EPA, “Ozone Generators That Are Sold as Air Cleaners.”