INTRODUCTION: Nontuberculous mycobacteria (NTM) are ubiquitous in our environment and can cause multiple pulmonary diseases, including nodulocavitary disease, interstitial disease, and hypersensitivity pneumonitis-like granulomatous lung disease. The latter disease is often referred to as ‘hot tub lung’ in the literature due to its association with exposure to NTM present in hot water aerosols primarily during indoor hot tub use by immunocompetent hosts. Diagnostic criteria include history of hot water aerosol exposure, recurrent symptoms coinciding with exposure, radiological evidence of bilateral ground glass or poorly defined centrilobular nodular opacities, bronchoalveolar lavage lymphocytosis and histological evidence of diffuse inflammatory infiltrates along interstitium and nonnecrotizing granulomas 1. Additionally, the same NTM species are isolated from respiratory samples and hot tub water. The disease usually resolves with abstinence from hot tub. Currently, there is still debate whether the disease represents infection by NTM or a hypersensitivity reaction to mycobacterial antigens or a combination of the two processes. While M. avium complex is the most common NTM causing ‘hot tub lung’; M. fortuitum has also been rarely implicated 3.
CASE PRESENTATION: We report the first-described case in the literature of M. asiaticum causing ‘hot tub lung’. Our patient is a 63 year old immunocompetent mechanical engineer who presented with a five month history of worsening dyspnea, nonproductive cough, fevers, and weight loss. Physical exam was notable for bilateral crackles in lung fields. His HRCT of the chest showed bilateral diffuse ground glass opacities and centrilobular nodules without significant mediastinal lymphadenopathy. Pulmonary function tests showed a restrictive pattern with decreased diffusing capacity. Prior to his evaluation, he was treated as an inpatient for atypical pneumonia with a macrolide antibiotic. Symptoms of dyspnea and cough improved during his hospitalization but recurred within a week of returning home. He was a lifelong nonsmoker, and had a cat and a dog as pets at home. He denied history of travel outside of New Mexico or of unusual occupational or environmental exposures. On further questioning, he stated he had daily use of an indoor hot tub that he had self-built a few years prior and patient often used the hot tub in place of his daily shower. In fact, he had increased his use of the hot tub since feeling poorly, as he thought it may help his symptoms. He underwent an outpatient bronchoscopy with transbronchial biopsies. Histological examination showed cellular interstitial pneumonitis and well-formed non-necrotizing granulomas. Bronchoalveolar lavage was smear negative but culture grew M. asiaticum. The patient abstained completely from his hot tub and was not given any pharmacological therapy. A month later, his symptoms resolved; he resumed his daily exercise routine of walking two miles. His Chest X-ray normalized though his pulmonary function abnormality improved but did not completely resolve two months out.
DISCUSSION:M. asiaticum was first reported as causing human disease in the early 1980s; since then only a few cases have been reported in the literature 2. The largest case series described 24 patients from Australia. All patients had either pre-existing bronchiectasis or underlying lung disease such as COPD and hot tub exposure was not described. Most patients were treated with anti-tuberculous drugs. In addition, there have been rare case reports of M asiaticum causing soft tissue infections or lymphadenitis. We present the first reported case in the literature of hypersensitivity pneumonitis-like granulomatous lung disease caused by M. asiaticum. We hypothesize that there is likely a common antigenic component among various NTM species that can trigger hypersensitivity pneumonitis.
CONCLUSIONS: Physicians need to be thus alerted to the possibility of ‘hot tub lung’ being caused by various NTM species other than M. avium complex.
Reference #1 Sood, Akshay et al. 2007. Hypersensitivity Pneumonitis-like Granulomatous Lung Disease with Nontuberculous Mycobacteria from Exposure to Hot Water Aerosols. Environmental Health Perspectives 115(2)262-266
Reference #2 Grech, Miriam et al. 2010. Clinical Significance of Mycobacterium asiaticum Isolates in Queensland, Australia. Journal of Clinical Microbiology 48(1) 162-167
Reference #3 Falkinham, Joseph O. 2003. Mycobacterial Aerosol and Respiratory Disease. Emerging Infectious Diseases 9(7) 763-767.
DISCLOSURE: The following authors have nothing to disclose: Theresa Heynekamp, Akshay Sood, Helen Busby
No Product/Research Disclosure Information