Tuberculosis 2021

2021 annual report on tuberculosis

  • 2021 saw a total of 208 notified cases of tuberculosis (TB) in Denmark. This case number prolonged the declining trend observed in the number of cases over the past ten years.
  • The TB incidence in Denmark was 3.5 cases per 100,000 inhabitants, but the regional incidence varied from 4.6 per 100,000 inhabitants in the Capital Region of Denmark to 2.4 per 100,000 inhabitants in Region Zealand.
  • 24% of the TB cases occurred in persons of Danish origin, whereas 76% occurred in persons of non-Danish origin.
  • The median age was 51 years for persons of Danish origin and 42 years for persons of non-Danish origin. Among persons of Danish origin, the highest case number was observed in the age group 50-69 years, whereas the largest number of cases among people of non-Danish origin was seen in the age group 30-49 years of age. Pulmonary TB remains the most frequent presentation (75%), whereas extrapulmonary forms of TB are still more frequent among persons of non-Danish origin.
  • Based on the notifications, a total of 86 cases (41%) presumably became infected in Denmark, whereas 98 cases (47%) were presumably infected abroad; and for 24 cases, (12%) the country of infection remains unknown.
  • An increase is still seen in the share of microscopy-positive patients (from 62% to 69% among Danes), which indicates delayed diagnostics leading to additional spreading of the infection.
  • A single case of “extremely resistant” (XDR) tuberculosis was detected; the third such case ever to be detected in Denmark.
  • A slight decrease was observed in the number of TB cases belonging to the infection chain “Cluster 2”, but its approx. 20% share of all cases remains very high and largely constant.

2021 saw a total of 208 notified cases of TB, including 122 men and 86 women. The median age for new cases was 47 years for males (range: 3-94 years) and 42 years for females (range 2-86 years).

In the past 10-year-period, the TB incidence has generally followed a declining trend, but a relatively larger decrease was seen in 2020 than in the previous years, Figure 1. The decrease observed from 2020 to 2021 follows the trend from previous years. Whether the 2020 decline was affected by COVID-19 lock-downs and/or poorer healthcare access is discussed in Tuberculosis - Report on disease occurrence 2019-20.

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National and regional TB incidence in 2021

The incidence was calculated based on population figures drawn from Statistics Denmark (STD).

In 2021, the total incidence of TB in Denmark was 3.5 cases per 100,000 inhabitants. The Capital Region of Denmark remains the region to record the highest incidence (4.6 per 100,000) and Region Zealand the lowest (2.4 per 100,000), Table 1. All regions have recorded a decline in incidence since 2012, but slight regional differences were observed. In the Capital Region of Denmark and Region Zealand, the incidence increased from 2020 to 2021, Figure 2.

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Origin and country of infection

The expression “of non-Danish origin” comprises immigrants and second-generation immigrants.

Among the 208 notified cases, 49 (24%) were persons of Danish origin: 33 men and 16 women. For persons of Danish origin, the median age was 51 years, range 16-84 years.

A total of 159 (76%) cases were notified among persons of non-Danish origin; 89 men and 70 women. For persons of non-Danish origin, the median age was 42 years, range 2-94 years.

Figure 3 shows the age distribution of TB cases in 2021, by origin. Among TB cases in persons of non-Danish origin, the highest number of cases was observed in the 30-49 years age group; and among TB cases in persons of Danish origin, the highest number was seen in the 50-69 years age group. This trend remains unchanged from previous years.

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Figure 4 presents the TB incidence in Denmark by the countries that recorded the highest TB incidences. As previously, the incidence was highest among persons from Greenland (239 per 100,000 in 2021) and Eritrea (153 per 100,000 in 2021).

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Presumed country of infection

Based on the notifications, 86 (41%) of the cases had probably become infected in Denmark and 98 (47%) abroad. For 24 cases, the country of infection was unknown. The distribution of cases infected in Denmark and abroad has remained unchanged for the past ten years, Figure 5.

Among persons of non-Danish origin for whom information was provided about country of infection, a total of 93 (66%) had become infected abroad and 48 (34%) in Denmark. The corresponding figures for TB cases in persons of Danish origin were five (12%) cases infected abroad and 38 cases (88%) infected in Denmark. Among those persons of non-Danish origin whose notifications stated that they had presumably become infected abroad, 91% (71 of 78) had probably become infected prior to their arrival to Denmark and 9% while travelling (tourist/business travels or stays with family and friends).

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TB localisation

Pulmonary TB is still the most frequently notified presentation among persons of Danish and non-Danish origin alike. Additionally, persons of non-Danish origin more frequently presented with extra-pulmonary types of TB than did people of Danish origin, particularly TB of the lymph nodes (glandular TB), Table 2.

Recurrence

A total of 14 patients (7%) were notified with recurrence. This figure remained unchanged from previous years when 6% (2020) and 7% (2019) of the cases were recurrences.

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TB and HIV infection

Among those notified with TB in 2021, six persons were HIV positives. In all, among the 208 TB cases notified, 101 persons had tested HIV negative, whereas the HIV status of the remaining 101 persons was not provided on the notifications. For these 101 persons, neither HIV notification to Statens Serum Institut (SSI) nor a HIV test result from the Danish Microbiology Database (MiBa) was available. This indicates that these persons had not undergone HIV testing in connection with their TB diagnostics. However, some test results stored in clinical-biochemical systems may not be accessible from the SSI.

TB in children

In 2021, a total of seven children below 15 years of age were notified with TB. The majority had presumably become infected in Denmark by a household member or by a close relative. All of these children were of non-Danish origin All children diagnosed with TB in 2021 had pulmonary TB.

Occupational transmission

In six cases, it was indicated that the person had presumably become infected while working. In 2020, the corresponding figure was three. None of the cases notified in 2021 worked in healthcare.

Microbiological trends

Compared with 2020, a continued increase was observed in the share of microscopy-positive pulmonary TB cases, i.e. in the share of TB patients with infectious pulmonary TB. The increase is more pronounced among people of Danish origin, where the share has increased from 62% to 69%. It remains unclear exactly what is causing the increase, but active screening activity in the risk environments has generally been reduced during the COVID-19 pandemic. Delayed diagnostics generally leads to more serious disease for the individual TB patient, which is reflected in the high share of microscopy-positive patients.

Among those notified for the first time, isoniazid mono-resistance was detected in nine (6%) patients. In 2021, no cases of multiple resistant (MDR) TB were detected, but one case of extremely resistant (XDR) TB was recorded. As stated above, a marked change is expected in 2022 as a total of 11 MDR TB cases have been recorded to date; see news item in Danish language (11 tilfælde af multiresistent tuberkulose i Danmark i år (ssi.dk) (11 cases of multiple resistant tuberculosis in Denmark this year to date (ssi.dk)). However, four of the 11 cases were detected before the patient arrived to Denmark.

Typing of bacteria from 146 of the 163 (90%) culture-positive patients detected in 2021 shows that a single chain of infection, ”C2/1112-15” (also known as Cluster 2), still dominates, accounting for 20% of all typed cases in Denmark. This indicates that the infection is still actively spreading in Denmark as the chain is typically seen among exposed Danes. A slight decrease was seen in the number of cases compared with 2020, but the share has remained largely stable and remains very high.

This report is also described in EPI-NEWS 44/2022.