An assessment of nucleic acid amplification testing for active mycobacterial infection

Background

Tuberculosis

Tuberculosis (TB) is an infectious disease caused by the bacterial genus Mycobacterium. The majority of disease is caused by MTB-complex species (including M. tuberculosis, M. africanum, M. bovis, M. microti, M. canettii, M. caprae, M. pinnipedii and M. mungi). However, disease caused by NTM, such as M. avium, M. kansasii, M. xenopi and M. malmoense, also occurs. It is a major global health problem; in 2012 an estimated 8.6 million people developed TB and 1.3 million died from the disease, including 320,000 deaths among human immunodeficiency virus (HIV)-positive people (WHO 2013). Even though Australia has a low rate of TB, with 4.7–6.5 cases per 100,000 population in 2010–12 (Lumb et al. 2013; WHO 2013), the total number of TB cases increased by 33% between 1998 and 2008, with most new cases occurring in arrivals from countries where TB is endemic (National Tuberculosis Advisory Committee 2012).

In Australia TB is a notifiable disease.National guidelines have been developed on the public health management of this disease (CDNA 2013). TB continues to pose ongoing challenges due to an increasing incidence of multidrug-resistant TB (MDR-TB) and extensively drug-resistant strains. A major concern articulated in the Australian Government TB policy is the entry into Australia of individuals infected with drug-resistant TB from Papua New Guinea via the Torres Strait (Marais, Sorrell & Britton 2012).

TB is transmitted through respiratory droplets from persons with active pulmonary or laryngeal TB. In rare cases invasion of MTB may occur through mucous membranes or damaged skin. It most commonly affects the lungs but may affect almost any organ or system, including the lymph nodes, central nervous system, liver, bones, genitourinary tract, and gastrointestinal tract (Cruz-Knight & Blake-Gumbs 2013; Garcia-Monco 2014). Extrapulmonary TB occurs in 10–42% of patients, depending on their ethnic background, age and immune status, as well as the presence or absence of underlying disease and the genotype of the MTB strain (Zumla et al. 2013). Table lists the clinical symptoms associated with the classic presentation of TB.

Table Clinical presentations of TB