No 50 - 2010

Tuberculosis 2009, part II

TB among Greenlanders in Denmark

An increase has been observed in the occurrence of TB among Greenlanders in Denmark.

The number of cases detected in 2009 was 40. In the 2006-2009 period, the number of Greenlanders in DK increased slightly. Taking into account such increase, the incidence up to and including 2008 was 200/100,000 after which it rose to nearly 300/100,000 in 2009.

The share of notified cases who were infected in Denmark has not increased in the same period, indicating a general increase in the TB occurrence among Greenlanders in Denmark.

The increase continues into 2010 and has currently reached nearly 400/100,000.

Microbiological diagnosis

In 2009 TB diagnosis was confirmed by culture and subsequent identification of species in 242 of 329 (74 %) notified cases, including 88 of 114 (77 %) Danish cases and 154 of 215 (72 %) immigrant cases. On the basis of the EU disease definition, EPI-NEWS 51/09 (pdf), a total of 242 (74 %) were confirmed cases, 14 (4 %) probable cases and 73 (22 %) were possible cases.

Among a total of 260 notified cases of pulmonary TB (± other localisation), 200 (77 %) cases were verified by culture, including 81 of 100 (81 %) Danish cases and 119 of 160 (74 %) immigrant cases.

Among 81 Danes with culture-verified pulmonary TB (± other localisation) and a minimum of one sputum or tracheal secretion test, 51 (63 %) had positive microscopy and were regarded as infectious. This proportion was 59 % in immigrants (70 of 119).

Tree immigrants had culture-verified M. africanum detected, the rest (239) had classical M. tuberculosis.

Resistance

Drug resistance results were available for all 242 culture-verified cases. Among 209 patients (77 Danes and 132 immigrants) notified with confirmed TB for the first time, 12 patients, five Danes and eight immigrants, had isoniazid mono-drug-resistance, and multi-drug-resistance was detected in one patient from Latvia (isoniazid and streptomycin).

Among 41 patients notified with previously treated TB, a total of three cases of isoniazid mono-drug-resistance were detected in one Danish and two immigrant patients.

MDR TB

In 2009, two cases of multi-drug-resistant TB (MDR-TB) were detected, i.e. as a minimum resistance to rifampicin and isoniazid and possibly to other antibiotics.

Furthermore, resistance to pyrazinamid and streptomycin was detected. A new case of non-infectious pulmonary TB was detected in a young Somalian male. DNA typing showed the same profile as that detected in an infectious Somalian with pulmonary TB in 2004, but no epidemiological link was established.

The second MDR case was detected in a previously treated Vietnamese male. He had disseminated disease including meningitis, and resistance to pyrazinamid, streptomycin and ethionamid was also established.

Presently, no cases of Extremely Drug Resistant TB (XDR-TB) have been detected in DK. The new WHO treatment outcome definitions on MDR-TB and non-MDR-TB are presented in Table 1.

New typing method

A new quick typing method has been introduced. It is known as "Mycobacterial Interspersed Repetitive-Unit — Variable Number of Tandem Repeats" (MIRU-VNTR), and is based on 24 loci in the mycobacterial DNA.

The MIRU-VNTR method has the same capacity of discrimination as the previously used, but time-consuming "Restriction Fragment Length Polymorphism" (RFLP) method. Results may be expected within 1-2 weeks after the specimen has turned culture-positive.

Comments to parts I and II

The overall trends in TB of the past decade have been favourable, Figure 1 (EPI-NEWS 49/10).

TB occurrence among immigrants from countries with a high TB occurrence has decreased by approx. 50 %, mirroring the decrease observed in immigration.

The occurrence among Danes has followed a slightly decreasing trend over the past 20 years to reach a historically low level in 2009. However, the decrease among Danes remains slower than that which may be expected in countries with a good national TB control programme, where an annual decrease in the order of 5-7 % is habitually seen.

The WHO's objective to eliminate TB (< 1 case per 1,000,000) by 2050 seems unrealistic despite the current trend. The slow decrease is primarily caused by the infection chain MIRU 1112-15 (RFLP cluster 2), seen among middle-aged Danish males who are socially exposed or suffer from alcohol dependence.

Traditional infection tracing remains necessary, particularly among the above-mentioned groups - and systematic monitoring of treatment outcomes is also essential. Furthermore, the efforts made to detect TB among Greenlanders in Denmark should be intensified.

2009 saw an unusually high number of occupationally infected and in none of these cases the source of infection could be identified. It is important that TB notification is accompanied by specific information on the source of infection so that infection patterns may be mapped by comparing the DNA types of isolates.
(D. Bang Mycobacteria Laboratory, P.H. Andersen, Dept. of Epidemiology)

Individually notifiable diseases and selected laboratory diagnosed infections (pdf) 

15 December 2010