A forty-six-year-old man suffered from a fever and nonproductive cough for 2 weeks. He noticed that his symptoms started two months after he started running an ultrasonic humidifier 24 hours a day in his home. He went to his local doctor and was prescribed medicine for bronchitis containing clarithromycin and amoxicillin. However, his symptoms worsened, and he visited our hospital in the winter, two weeks after his first visit. The patient, who was a smoker (10 pack-years), had a medical history of depression and sleep apnea syndrome, without medical treatment. His occupation was an automotive maintenance engineer.
His vital signs on admission showed a low grade fever of 37.0 , moderate tachycardia of 98 beats per minute, tachypnea of 20 times/min, and hypoxemia with an oxygen saturation level of 88% on ambient air. Physical examination revealed no abnormalities except for inspiratory late crackles in both lung bases. An arterial blood sample showed a PaCO2 of 36.9 mmHg and a PaO2 of 59.8 mmHg. The laboratory findings showed an increased white blood cell count of 10700/muL with 72.8% polymorphic nuclear leukocytes and a C-reactive protein (CRP) concentration of 7.24 mg/dL. His serum levels of KL-6 (674 U/mL) and SP-D (151 ng/mL) were slightly elevated. The serum antibodies against Trichosporon asahii and Aspergillus were negative. Chest high-resolution computed tomography (CT) showed bilateral diffuse subpleural nonsegmental ground-glass opacities (Fig. 1). The pulmonary function test showed a restrictive pattern (predicted forced vital capacity 75.9%) with moderately reduced diffusion capacity (% single-breath carbon monoxide diffusing capacity 71.5%).
Based on the clinical course and the findings of the examinations, we suspected HP associated with the ultrasonic humidifier and performed flexible bronchoscopy to obtain a definitive diagnosis. The bronchoalveolar lavage fluid (BALF) revealed an elevated cell count (16.4 x 106/mL) with lymphocytes (51.0%), neutrophils (11.4%), and eosinophils (8%). The ratio of CD4+ to CD8+ cells (CD4/8) of BALF was 1.60, which was normal. The histological examination of the transbronchial lung biopsy (TBLB) showed alveolitis with the infiltration of lymphocytes and plasma cells without granulomas or Masson bodies. We performed an inhalation challenge test with the ultrasonic humidifier (Fig. 2). Six hours after the test, he developed a high fever (38.1  Celsius), chills and dyspnea. The blood tests showed an increased white blood cell count (29950/muL) and CRP level (4.85 mg/dL) on the following day, while the serum KL-6 level did not change. Accordingly, we diagnosed the patient with humidifier lung. His symptoms, laboratory findings, and radiographic findings gradually improved after avoiding the use of the humidifier without taking medication.
Acinetobacter junii, Bacillus spp, Cladosporium cladosporioides, Fusarium graminearum, and Mycobacterium gordonae were isolated from the humidifier water, while no pathogens except for normal flora were isolated from the BALF. The concentration of endotoxin in the humidifier water was high (more than 5000 pg/dL) (Table 1).
Chest high-resolution computed tomography (CT). . The chest CT showed diffuse subpleural nonsegmental ground-glass opacities.