Eurosurveillance

ECDC

Tuberculosis in Denmark, 2000

 Rediger
 1 Published: 19.08.04 Updated: 19.08.2004 14:00:48
V. Thomsen, P. Andersen

In 2000 a total of 548 tuberculosis cases were notified in Denmark, as compared with 536 cases in 1999. The overall incidence was 10,3 per 105 . Cases notified from Greenland or the Faroes are not included. An immigrant is defined as a person born abroad or a person under 25 years of age born in Denmark to parents, one or both of whom were born abroad. Greenlanders resident in Denmark are classified as immigrants. On 1 May 2000 the notification criteria for TB were extended to include the entire Mycobacterium tuberculosis complex, i.e. M. tuberculosis, M. africanum, M. microti  and  M. bovis  excluding the BCG strain, 199 cases were notified in native Danes. The incidence in Danes rose to  4,0 per 10 from 3,3 per 105  in 1999. This rise was seen in all age groups, but especially in 15-39-year olds. The male/female  ratio was  2:1. 349 cases were notified in immigrants, with an male/female  ratio of 1:1. The incidence  fell from 102,6 per 105  in 1999 to 92,3 per 105 . Immigrants from Somalia still constituted by far the largest group (47%), followed by Pakistan (10%), Greenland (4%), and 3% each from Turkey, Iraq and Afghanistan.

Compared with the 5-year period 1995-1999, the largest numerical rises were seen in the counties of  Funen (total incidence 13,1, among Danes 4,5 and immigrants 153,6 in 2000), Copenhagen (total incidence 28,0 among Danes 11,7 and immigrants 107,6 in 2000) and Ringkøbing (total incidence 8,4, among Danes 4,2 and immigrants 109,9 in 2000) while the largest falls occurred in West Zealand and North Jutland counties. The rise in Funen was partly due to a doubling of cases in Danes in 2000 in comparison with the previous five years. No major outbreaks were noted.

Localization

397 patients (72%) had pulmonary TB, of  whom 37 also had TB elsewhere. Among native Danes, 174 (87%) had pulmonary TB, the figure for immigrants being 223 (64%). The commonest extrapulmonary manifestations, with or without pulmonary TB, were TB in lymph nodes (14%), bones (5%), intestine (4%) and pleura (3%). 13% of Danes (25) had exclusively extrapulmonary TB. This proportion was 36% in immigrants (126).  This group thus continued to make up a large proportion of cases of extrapulmonary TB. Seven patients, all immigrants, had miliary TB, and five, including two Danes, had tuberculous meningitis.

Risk groups

11 patients, four Danes and seven immigrants, were stated to be HIV positive. Alcohol abuse was noted in 29 patients,  25 Danes and four immigrants. These 25 Danes comprised 18 men and seven women with a median age of 43 and 51 years respectively.

Transmission

Most Danes with TB (93%) were thought to have been infected in Denmark and the majority of immigrants (88%) abroad, typically in their country of origin, 41 immigrants were thought to have been infected in Denmark, including 16 from Somalia, nine from Greenland and five from Pakistan.  13 Danes were stated to have been infected abroad, five in Asia and three in Africa.  39 patients were notified with relapse, 17 Danes (12%) and  22 immigrants. A source of infection within the household during the previous three years was noted in 51 cases (nine Danes and 42 immigrants). A source of infection outside the household during the previous three years was noted in  further 50 cases (31 Danes and 19 immigrants). In 32 patients, 12 Danes and 20 immigrants, a possible infective contact had occurred more than three years earlier. In 376 cases (70%) the source of infection was unknown.
Occupational infection
Nine Danish patients were possibly infected at their place of work; eight of these had positive culture for TB. Two were teachers who had taught refugees; one of these had been subject to exposure two  years previously. In only one case did DNA typing support a source of infection at work. In the seven other cases  in which DNA typing was   possible, no evidence of a definite occupational source of infection was obtained.
Outbreaks

Some small outbreaks  comprising two of three patients were noted. There were four outbreaks with four or more patients each:

  • Nine Somalis, Including seven children. Isolates from the seven cases with positive culture showed the same DNA profile.
  • Four Kosovo-Albanians, including three children below the age of nine years. Isolates from the two cases with positive culture had the same DNA profile.
  • Four Somali siblings aged 11-17 years, all stated to be infected prior to arrival in Denmark. Isolates from the two cases with positive culture had the same DNA profile.

Microbiological diagnosis

The diagnosis was  confirmed by culture in 432 cases (79%), which represents a continuing decline from 1995-99, when the average was 85%. The proportion (316/397) of culture-confirmed cases for pulmonary TB was not significantly different from that for extrapulmonary TB (116/151). In patients with pulmonary     TB (± other localization), the diagnosis was culture-confirmed in 86% of Danish and 74% of immigrant patients. In those with extrapulmonary TB, the corresponding proportions were 76% and 77%. In 42 children below 15 years of age the diagnosis was culture-confirmed in 27 cases (64%). Mycobacterium bovis was found in five Danes: one had pulmonary TB, three had TB of bone and one had  urogenital TB.  13 patients initially notified as having TB were later found to have non-tuberculous mycobacteria on culture. In three cases the diagnosis of TB was upheld on clinical grounds. Of all patients with culture-positive pulmonary TB (± other localization), 186 (59%), comprising 105 Danes and 81 immigrants, had positive microscopy in at least one pulmonary specimen and were regarded as infectious. Positive microscopy in patients with culture-positive pulmonary TB was found in 70% of Danish and 49% of immigrants cases. For patients with culture-confirmed TB, the microbiological diagnosis was made by microscopy (±PCR) in 186 patients (59%) with pulmonary TB (± other localization)  and in 28 patients (24%) with  extrapulmonary TB. PCR for   M. tuberculosis complex was carried out on 28% of all specimens received  and identified a further 46 patients (11%): 27 with pulmonary TB (± other localization)  and 19 with extrapumlonary TB. In 260 patients (60%) provisional diagnosis could thus be made by microscopy of confirmed by PCR within days of receiving the specimen, while diagnosis had to await culture results in 172 cases (40%).

Drug resistance

Resistance to at least one of the primary antituberculous drugs (rifampicin (R), isoniazid (I), ethambutol (E), pyrazinamide (P) or streptomycin (S) was demonstrated in 64 patients (15%) with  culture-confirmed TB, comprising 13 Danes and 51 immigrants. Of 39 patients with relapse, 10(26%) had resistant TB. The remaining 54 patients TB were diagnosed for the first time or information on previous TB was lacking. Monoresistance was demonstrated in 36 patients (8%), to isoniazid in 11 cases (10 immigrants and one Dane), to streptomycin in 18 cases (15 immigrants and three Danes) and to pyrazinamide in seven cases (two immigrants and  five Danes). In five cases pyrazinamide monoresistance was due to  M. bovis, which is naturally resistant to this agent. Resistance to  two or more drugs was demonstrated in 28 patients (6%); I+S in 24 cases (20 immigrants and four Danes), and in one case each to I+E, I+E+P, R+I+E and R+I+E+P+S. These last four cases were in immigrants. Thus two patients were  notified as having multi-drug-resistant (MDR) TB, defined  as TB resistant to at least rifampicin and  isoniazid.
 A Somali woman who arrived in 1998 had MDR TB demonstrated in a cervical lymph node. The DNA profile of the TM isolate was identical with that from other Somali patients  without MDR TB.
 An Iraqi man had fully sensitive TB in 1994, but then developed first isoniazid resistance and then rifampicin and ethambutol resistance as well. After prolonged treatment with secondary drugs, he fell ill again in 2000, having had six negative cultures in 1998-99. All the TB isolates from this patient had an identical DNA profile from 1994 to 2000, which points to relapse. In addition, a Danish man who had been notified in 1999 with rifampicin monoresistant TB, developed MDR TB in 2000.

Comments

The rise in number of TB cases over those of 1999 (536) can be attributed in part to the extended criteria for notification. The number of cases in Danes has risen again, but has previously been at this level during the period 1995-99. Reporting of the number of infectious patients is now based on all primary specimens received, and not as earlier, just on the one specimen that first showed growth of  M. tuberculosis.  Danish patients with infectious (open) pulmonary TB make up a larger group than the equivalent immigrant group, in both relative and absolute terms. The proportion of patients with  resistant TB is comparable with that for the three preceding years, but is still high in relation to 1991-96. The decline in the number of culture-confirmed cases is probably due to the fact that fewer specimens were cultured for mycobacteria. The decline cultured in 2000. Culture and species determination is a prerequisite for the definitive from 30 480 specimens cultured in 1993, is continuing, 19 891 specimens being diagnosis of TB, as well as for DNA fingerprinting and resistance determination. It is unfortunate that it is impossible to determine resistance in an ever increasing number of cases.
( EPI-NEWS 43/44/2001)


 


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