20 Tuberculosis

20.3 Epidemiology

20.3.1 Global burden of disease

Worldwide the incidence rate of TB is slowly falling by about 2 percent per year, but tuberculosis remains a major global health problem.4 The WHO estimates there were 8.6 million new TB cases in 2012 and 1.3 million deaths; 320,000 of these deaths were in HIV-positive individuals.4 The majority of the TB burden exists in 22 high-burden countries.4

The peak age for TB infection in most Western countries is adults over 50 years. However, among ethnic and racial minorities, rates are higher and often more common in young adults and children. Certain environments tend to make TB incidence much higher: poverty, poor nutrition, poor access to health care and crowded conditions.

20.3.2 New Zealand epidemiologyTop

The overall rate of active TB in New Zealand is low compared with many countries, although TB remains one of the most common notifiable infectious diseases. Cases of TB in New Zealand declined substantially between 1980 and 2007, but they have remained relatively stable since then (Figure 20.1).5 In 2013 there were 278 notifications (6.2 per 100,000 population), compared to 294 notifications in 2012 (6.6 per 100,000).

Most cases in 2012 were associated with people born in Asia, Africa and the Pacific Islands, particularly recent immigrants from these areas. Risk factors for being diagnosed with TB include being born overseas in a high-prevalence country, recent immigrant, prior or recent contact with TB, and identified as living in an area of higher deprivation.5

Figure 20.1: Notification rate of tuberculosis disease, 1980–2013

Figure 20.1: Notification rate of tuberculosis disease, 1980–2013

Source: Institute of Environmental Science and Research

Bovine infection with M. bovis has spread to feral possums, placing cattle and deer herds at risk. At present, because of herd testing and the widespread pasteurisation of milk, this causes very few cases of human M. bovis disease (fewer than 10 cases were reported each year between 2008 and 2012).

In 2012 there were 294 TB notifications, including 279 new cases and 15 relapses/reactivations. The 2012 notification rate was 6.6 cases per 100,000 population, a slight decrease from the 2011 rate (7.0 per 100,000). Ethnic-specific notification rates were higher in the Asian (41.4 per 100,000) and Middle Eastern/Latin American/African (31.8 per 100,000) ethnic groups, lower for Pacific peoples (12.4 per 100,000) and even lower for Māori (5.4 per 100,000) and European/Other (0.9 per 100,000) groups. Over 60 percent of new cases resided in the four most deprived deciles (NZDep 7–10). There is significant regional variation in rates.5

Of the 279 new TB disease cases in 2012, 65 were born in New Zealand and 214 were born overseas. The highest disease rate was among those born in Southern and Central Asia (152.5 per 100,000), followed by those born in South-East Asia (89.2 per 100,000), then the Pacific Islands (21.3 per 100,000) and Sub-Saharan Africa (20.3 per 100,000).5

The most commonly reported risk factor was being born overseas (76 percent of all cases) and current or recent residence with a person born outside of New Zealand (68.8 percent of cases). Prior contact with a confirmed case of TB was recorded in 21.6 percent of cases.5

The date of arrival was recorded for 181 of the 214 new TB cases born outside of New Zealand. The interval between the date of arrival and the TB notification date ranged from two days to 64 years, with a mean interval of 7.7 years and median interval of 4 years (Figure 20.2).5

Figure 20.2: Tuberculosis notifications (new cases) born outside of New Zealand, by number of years since arrival in New Zealand, 2012

Figure 20.2: Tuberculosis notifications (new cases) born outside of New Zealand, by number of years since arrival in New Zealand, 2012

Note: The date of arrival was not recorded for 38 cases.

Source: Institute of Environmental Science and Research