A Prospective Observational Study of Parameters Related to the Clinical Outcomes of NTM Pulmonary Disease in Prince of Wales Hospital

Non-tuberculous mycobacteria (NTM) are a large group of ubiquitous microorganisms in the natural environment as well as household water systems . Over 180 different species have been identified but only 32 are reported to cause diseases in human or animals. NTM infection can affect the lung, skin and soft tissue, lymph node or cause disseminated diseases in the immunocompromised. NTM pulmonary diseases are the most important disease entity, accounting for 75-94% of all clinically important NTM cases.

The predominant species and their pathogenicity vary in different countries. While Mycobacterium avium-intracellulare complex (MAC) is most prevalent in the USA, Canada, Australia, Japan, Taiwan and Hong Kong, M. abscessus complex is more common in Singapore and M. Kansasii in European counties, respectively. Recently reports showed an increasing trend in importance of NTM PD in a few countries.

NTM can cause chronic and debilitating pulmonary disease with increased morbidity and even mortality. Healthy individuals can be affected though many have underlying structural lung diseases or immunodeficient conditions. Patients usually present with nonspecific symptoms, including productive cough, dyspnea, hemoptysis, fever, weight loss and malaise. Therefore, the diagnosis of NTM pulmonary disease (NTMPD) is challenging requiring comprehensive clinical, microbiological and radiological data according to in the American Thoracic Society and Infectious Diseases Society of America (ATS/IDSA) 2007 guidelines. Treatment of NTMPD is also a difficult decision because some remain stable for a long period without treatment while the others progress to severe and even fatal diseases. A prolonged course of antibiotic involving multiple agents with potential adverse effects is needed but a cure cannot be guaranteed. Moreover, the treatment regimens might be different from those recommended by the international guidelines after balancing multiple factors, including patients' comorbidities, disease severity, and the species and antimicrobial susceptibility of the causative organism. Therefore, whom to treat, when to start and how to treat is a clinical dilemma. Epidemiological data of NTM remains unclear although an increase in prevalence and incidence are consistently observed globally. It is not a notifiable disease in most of the countries and data mainly comes from sentinel surveillance and microbiological results.

Local epidemiological data of NTM infection in Hong Kong is largely scarce apart from a small study done 25 years ago in 1995. Further local investigation on the epidemiology, disease course and clinical practice is needed to optimize their management.