Pulmonary Nontuberculous Mycobacterial Disease: Changing Epidemiology : Abstract and Introduction

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Changing Epidemiology of Pulmonary Nontuberculous Mycobacteria Infections CME
Rachel M. Thomson, MD

Authors and Disclosures

CME Released: 09/21/2010; Valid for credit through 09/21/2011

Abstract
Nontuberculous mycobacteria (NTM) disease is a notifiable condition in Queensland, Australia. Mycobacterial isolates that require species identification are forwarded to the Queensland Mycobacterial Reference Laboratory, providing a central opportunity to capture statewide data on the epidemiology of NTM disease. We compared isolates obtained in 1999 and 2005 and used data from the Queensland notification scheme to report the clinical relevance of these isolates. The incidence of notified cases of clinically significant pulmonary disease rose from 2.2 (1999) to 3.2 (2005) per 100,000 population. The pattern of disease has changed from predominantly cavitary disease in middle-aged men who smoke to fibronodular disease in elderly women. Mycobacterium intracellulare is the main pathogen associated with the increase in isolates speciated in Queensland.

Introduction
Worldwide, pulmonary disease caused by nontuberculous mycobacteria (NTM) appears to be increasing,[1–4] yet accurate data to support this assumption are difficult to produce. Patients traditionally described are middle-aged men with underlying chronic lung disease, such as chronic obstructive pulmonary disease, who have upper lobe cavity formation and nodules of various sizes. An increasing number of patients have nodules, bronchiolitis, and bronchiectasis involving the middle lobe and lingula. These patients are more commonly female nonsmokers and have no preexisting lung disease.[5,6]

NTM disease is not a reportable condition in most countries because no evidence of human-to-human transmission exists; therefore, it is not considered a public health concern. However, the organisms are ubiquitous in the environment, and substantial evidence shows that the environmental niche for Mycobacterium intracellulare (the most common pulmonary pathogen) is in biofilms lining suburban water pipes. Many NTM pathogens have been isolated from drinking water.[7] Some clinicians believe the condition should be classified as an environmental health concern, similar to that caused by Legionella spp.

Globally, geographic variability in environmental exposure and prevalence of NTM disease is significant.[8] Without detailed clinical information, differentiating between contamination of specimens, colonization/infection, and disease is difficult; laboratory reports of isolates do not always reflect the true incidence of disease. To determine if disease is present, sputum specimens and often a bronchoscopic sample of a patient’s lower respiratory tract must be collected. In addition, computed tomography scanning and clinical appointments with primary care providers and specialists are needed. Because this investigative process is costly to the healthcare system and the patient, accurate epidemiologic data on this condition should be of interest to public health experts.

Studies of avian versus human Mantoux testing in schoolchildren have shown that exposure to NTM organisms is common in Queensland.[9–11] Therefore, since the introduction of TB control services, disease caused by NTM in Queensland has been notifiable. This practice has been continued primarily to avoid confounding of smear-positive cases with TB. The notification process provides a unique opportunity to study the clinical significance of isolates positive for NTM and the features such as age and sex, symptoms, underlying conditions, and radiology results of patients with disease, avoiding the inherent bias that occurs in case series that are reported by tertiary and quaternary referral centers. The incidence of clinically reported cases of pulmonary disease caused by M. avium complex (MAC) in Queensland has been increasing (1985, 0.63/100,000 population; 1994, 1.21/100,000; and 1999, 2.2/100,000). In 2005, the Queensland Tuberculosis Control Centre (QTBCC) revised the notification process to ensure collection of meaningful clinical data and follow-up of clinically significant NTM cases.

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Pulmonary Nontuberculous Mycobacterial Disease: Changing Epidemiology : Abstract and Introduction