Household mold linked to 1 in 4 hypersensitivity pneumonitis cases

Mold thrives where moisture lingers. Spores can flourish after floods, heavy rains, or the unseen drip of a leaky pipe, turning bathrooms, bedrooms, and air-conditioning units into fungal incubators. Behind drywall, around air vents, and in the corners of poorly ventilated basements, mold finds ideal conditions to grow, driven in part by climate-driven weather changes meeting ill-prepared or aging home construction.

University of Texas Southwestern Medical Center–led investigators report that one in four hypersensitivity pneumonitis cases in their interstitial lung disease registry could be traced back to mold inside patients’ homes, identifying chronic exposure to residential mold as a potential source of severe immune-mediated lung condition.

Household exposure has been associated with a range of illnesses, including asthma, chronic rhinosinusitis, and allergic bronchopulmonary mycosis. Physicians are often unable to connect residential environments with patient symptoms, in part due to limited diagnostic tools for mold-related illness. Without clear exposure histories or validated testing methods, the role of mold in respiratory disease remains easy to miss.

In the study, “Hypersensitivity pneumonitis associated with home mold exposure: A retrospective cohort analysis,” published in PLOS ONE, researchers retrospectively examined records from patients diagnosed with hypersensitivity pneumonitis to identify those with confirmed residential mold exposure.

Medical records came from a single-center interstitial lung disease registry in Dallas, Texas, where 231 patients had been diagnosed with moderate to definite hypersensitivity pneumonitis between 2011 and 2019. Of the 231 patients, most in their early sixties, 54 had mold exposure inside their Texas residences, with 90% showing fibrotic disease and nearly 41% requiring oxygen support.

Diagnostic confidence rested on multidisciplinary review of high-resolution computed tomography, bronchoalveolar lavage lymphocyte counts, transbronchial or surgical lung biopsies, alongside a structured exposure questionnaire administered by pulmonologists trained in occupational assessment. Mold removal was verified when contaminated porous materials were cleared and water intrusion was fixed or when patients relocated.

Mold resided chiefly in bathrooms, bedrooms, or central air-conditioning systems, usually after chronic pipe or roof leaks. Invasive testing supported the diagnosis in about 86% of cases. Lung transplant-free survival averaged 97.7 months, mirroring outcomes in patients exposed to outdoor mold or birds.

Among 41 patients who eliminated household mold, five achieved more than 10 % gain in forced vital capacity within four months, including four with fibrotic disease, and none experienced significant decline.

Of those who eliminated mold exposure, 12.2% experienced marked improvement in lung capacity within months, including patients with fibrotic disease, traditionally thought less responsive to intervention. No patients worsened following exposure removal. Transplant-free survival reached a median of 97.7 months—comparable to patients exposed to avian antigens or mold outside the home.

Researchers conclude that home mold represents an under-recognized but modifiable cause of hypersensitivity pneumonitis. They urge clinicians to expand exposure histories and consider environmental assessments in patients with compatible imaging or respiratory symptoms.

Given projected increases in flooding and heat-induced mold growth, public awareness and clinical vigilance may become increasingly urgent.

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