This 49 year old patient was admitted with several weeks of worsening dyspnoea and dry cough. He had no history of previous respiratory illness. Further history revealed that several months prior he and his wife installed a hot tub in their bathroom. His HRCT chest showed widespread areas of ground glass opacity. Bronchoalveolar washings grew mycobacterium avium intracellulare (MAI). The diagnosis of hot tub lung was made and the patient’s symptoms rapidly resolved with corticosteroids. Interestingly, his wife was admitted with similar symptoms a few weeks later.

Hot tub lung is a hypersensitivity pneumonitis to MAI. MAI grows well in high water temperatures and is inhaled when the organism is aerosolised by the bubbles and steam generated from the hot tub. Poor hot tub maintenance with infrequent cleaning and changing of the filters contributes to the disease.

Hypersensitivity pneumonitis (extrinsic allergic alveolitis) is a hypersensitivity reaction to inhaled antigens. In the acute setting it is a type 3 hypersensitivity reaction that causes acute interstitial changes, most commonly ground glass opacities or centrilobular nodules, with a predilection for the lower lobes. Resolution occurs with removal of the offending agent +/- corticosteroids. In the chronic setting it is a type 4 hypersensitivity reaction that causes progressive pulmonary fibrosis with a predilection for the upper lobes.

1.Rickman OB, et al. Hypersensitivity Pneumonitis Associated With Mycobacterium avium Complex and Hot Tub Use. Mayo Clinic Proceedings 2002;77:1233-1237
2. Weissleder R, et al. Primer of Diagnostic Imaging. 3rd edition, Mosby 2003

Credit: Dr Donna D’Souza