A 66-year-old woman was taking drugs meant to calm an overactive immune reaction in her lungs, but her lung disease was not getting better. The likely reason turned out to be inside her home: an indoor hot tub she used every day.
The case, published Sept. 15 in Respirology Case Reports, describes a patient first diagnosed with hypersensitivity pneumonitis, an inflammatory lung condition triggered by inhaled substances. Only after a lung biopsy and a closer look at her daily habits did doctors identify the probable culprit, Mycobacterium avium complex (MAC), a group of environmental bacteria that thrive in warm water.
After the exposure stopped and she began antimycobacterial treatment, her symptoms and lung scans eventually cleared completely, according to the report.
A Diagnosis That Was Close but Incomplete
Hypersensitivity pneumonitis was not a wild guess. The illness known as hot tub lung closely resembles it, and doctors have long debated whether hot tub lung is mainly an allergic-type reaction to inhaled bacteria, a true infection, or a mix of both.
In this case, standard immune-suppressing therapy did not bring improvement. A lung biopsy then showed granulomas, small clusters of immune cells that form around something the body is trying to wall off. Inside them, pathologists found a small number of MAC organisms.
That finding sent the medical team back to the patient's history. A detailed review of her exposures uncovered her daily use of an indoor hot tub, a setting repeatedly tied to the disease in the medical literature.
Warm Water, Jets and a Room Full of Mist
MAC bacteria are common in water, and people frequently inhale them, but they rarely cause illness in healthy people. Hot tubs change the equation because warm water and powerful jets can turn the bacteria into a fine mist that lingers in enclosed spaces.
A 2007 review in the NIH-published journal Environmental Health Perspectives described hot tub lung as a granulomatous lung disease seen in people with normal immune systems after exposure to hot water aerosols from hot tubs, showers, and indoor pools. The authors noted that prevention relies largely on ventilation and good use practices. Mayo Clinic researchers have also pointed out that chlorine loses much of its disinfecting power in water warmer than about 84 degrees Fahrenheit.
Those Mayo researchers reported two cases in 2002 in Mayo Clinic Proceedings. Both patients kept using their hot tubs as their breathing worsened. Both had received steroids based on biopsies that suggested other diagnoses, sarcoidosis in one and eosinophilic bronchiolitis in the other, with little improvement. Once they stopped using their hot tubs, both improved quickly, without antimycobacterial drugs.
A Disease That Hides Behind Other Labels
Mistaken identity appears to be common. In a Mayo Clinic series of 21 patients with hot tub lung, the most common diagnoses patients arrived with were sarcoidosis, bronchitis, and asthma. Every patient improved once exposure stopped. Along the way, 13 received corticosteroids, one received antimycobacterial drugs, two received both, and five needed no medication at all.
The typical symptoms, cough and breathlessness, overlap with many common lung problems. Imaging can mislead, too. A CT study of 12 patients with hot tub lung, published in the American Journal of Roentgenology, found hazy ground-glass areas, small nodules and air trapping that looked much like findings in hypersensitivity pneumonitis. Patients in that study ranged from 13 to 66 years old, a reminder that the disease is not confined to one age group. Without a specific question about hot tub use, the key clue can go unasked.
The new case adds a treatment wrinkle. The authors of the 2006 Mayo series concluded that antimycobacterial drugs did not appear necessary for most patients. This patient, however, received antimycobacterial therapy along with exposure removal, reflecting ongoing uncertainty about how to manage cases in which organisms are seen in lung tissue and anti-inflammatory treatment has not worked.
A single case cannot settle that debate. It does show how biopsy findings and a careful exposure history can redirect care when a patient is not responding.
Keeping Hot Tubs from Becoming a Lung Risk
Hot tub lung is considered uncommon, and most hot tub users will never develop it. Still, warm water systems can harbor more than one lung threat. The CDC has linked poorly maintained hot tubs to Legionnaires' disease, including two outbreaks tied to private balcony hot tubs on cruise ships that sickened 12 travelers.
Owners can lower their risk by following manufacturer and public health guidance on disinfectant levels, filter changes, draining, and cleaning. Good ventilation matters for indoor units.
Anyone who develops a persistent cough, unexplained shortness of breath, fatigue, or fever, especially after regular hot tub, spa, or indoor pool use, should mention that exposure to a clinician. It may be the single detail that changes the diagnosis.
Key Questions Answered
What is hot tub lung?
It is a lung disease linked to inhaling mist containing nontuberculous mycobacteria, most often Mycobacterium avium complex, from hot tubs and similar warm water sources.
Why did the woman's first treatment fail?
She was treated for hypersensitivity pneumonitis with immunosuppressive drugs while her hot tub exposure continued. She improved after the exposure stopped and she received antimycobacterial treatment.
Is hot tub lung contagious?
No. It comes from environmental exposure to contaminated water mist, not from contact with another person.
Does everyone with hot tub lung need antibiotics?
Not necessarily. In earlier studies, many patients improved with exposure avoidance alone or with steroids. Treatment decisions depend on the individual case and should be made with a lung specialist.
What should hot tub users watch for?
A lingering cough, worsening shortness of breath, fatigue or fever. People with these symptoms should tell their clinician about hot tub or spa use.
