Hypersensitivity pneumonitis caused by a hidden antigen

We present the case of a 28-year-old patient suffering from progressive exertional dyspnea for about 5 months. A previous atypical pneumonia had taken a prolonged course in spite of antibiotic therapy. Main symptoms were tachypnea, cyanosis and inspiratory crackles. The chest X-ray showed interstitial pneumonia, and lung function testing showed a severe hypoxemia and a reduced diffusing capacity. In the bronchoalvealar lavage, performed within the first 24 hours after exacerbation, an neutrophilic alveolitis was found. The CT thorax showed a diffuse groundglass shadow with partial fibrotic changes. Serologically, specific IgG against moulds were found, particularly against Aspergillus fumigatus. Although the patient showed the clinical findings of hypersensitivity pneumonitis and serological evidence sensitization against Aspergilli, there was no visible mould infestation in the patient's environment. The diagnosis of hypersensitivity pneumonitis, the hidden causative allergen, could be confirmed when measurements in the patient's environment revealed a hidden focus of Aspergillus fumigatus.