NTM to blame for outbreak of ‘hot tub lung’

Infectious diseases

By Michael Woodhead

12 Nov 2020

Respiratory specialists in Queensland say vigilance is needed for ‘hot tub lung’ following a cluster of five cases in family members secondary to aerosolised non‐tuberculous mycobacteria (NTM) from an indoor swimming pool.

The diagnosis of NTM proved to be a challenge, according to Dr David Deller and Dr Matthew Corbitt of the Gold Coast Respiratory & Sleep Clinic, who said the case came to light after a 17-year old previously healthy young man was hospitalised for breathing difficulties, cough and fever.

Writing in Respirology Case Reports, they said the patient had tachypnoea with exercise‐induced hypoxaemia (SpO2: 82%) and supplemental oxygen was required via nasal cannula at 3 L/min to maintain oxygen saturations above 90%. On examination, there were extensive crackles bilaterally on chest auscultation without additional signs of heart failure.

Pulmonary function tests showed a restrictive pattern of impairment with significant reductions in FEV1 of 2.52 L (64% predicted), FVC of 3.42 L (72% predicted) without bronchodilator reversibility, and DLCO of 19.54 mL/min/mmHg (67% predicted). A CT scan of the chest demonstrated bilateral, symmetrical, diffuse patchy ground‐glass opacities with associated small volume adenopathy; however, no micronodularity was seen.

Microbiological tests were all negative.

Further investigation revealed that four other members of his family had also experienced persistent cough with varying degrees of dyspnoea and had gas transfer values of 50–60% predicted with radiological changes consistent with NTM disease.

After extensive investigations by local authorities, Mycobacterium intracellulare was cultured from the indoor pool water, and also from washings of the patient’s BAL sample.

The underlying cause of the NTM was presumed to be a switch from chlorine to non-chlorine disinfection system of the indoor pool in the family home.

The patient was managed conservatively, without antimicrobial or steroid treatment and made a gradual recovery , with his lung function tests improving to become stable at low normal values after two years.

“This case highlights the importance of considering environmental sources of pulmonary injury when disease clusters are encountered,” the report authors said.

They noted that NTM are found widely in the environmental including soil and water supplies, but respiratory transmission is usually uncommon. However NTM can be aerosolised and inhaled as part of steam from hot tubs or similar, and this appeared to be the case in the cluster in the family from the indoor pool.

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