Meningococcal Disease 2021

2021 Annual Report on Meningococcal Disease

In Denmark, invasive meningococcal disease (IMD) is clinically notifiable via the clinical notification system (SEI2) of the Danish Health Authority, and surveillance is handled by the Department of Infectious Disease Epidemiology and Prevention and by the Neisseria and Streptococcal Reference Laboratory, which receives meningococcal isolates and other biological material from the departments of clinical microbiology. IMD covers meningitis, bacteremia and culture or DNA detection of meningococci in material from normally sterile locations, e.g. joints.

In 2021, the Department of Infectious Disease Epidemiology and Prevention received 10 notifications concerning patients with invasive meningococcal disease. A reminder had to be sent out to ensure notification in three of the cases (30%).

Geography, sex and age

In 2021, the IMD incidence was 0.2 per 105 inhabitants, which constitutes a decrease compared with previous years when the incidence was 0.3 (2020) and 1.0 (2019). The limited number of cases was not clustered in a single Danish area. The incidence in the areas where cases were recorded varied from 0.2 to 0.3 cases per pr. 105 inhabitants.


IMD occurred in most age groups, see Table 2. The median age was 26 years (range 1-67 years). The highest incidences were recorded among patients aged 1-2 years. Please note that the incidence was calculated based on very few cases. Slightly more men than women had MD at an M/W ratio of 1.5.



Assessed on the basis of findings in and the type of sampling material, four patients had meningitis and two had meningitis and sepsis.

A total of six patients had IMD caused by group B (60%), two by group C (20%) and one by group W (10%). For one patient, the diagnosis was made exclusively based on the clinical picture (10%).

All patients had become infected in Denmark.

Following the introduction of restrictions aiming to limit infection with SARS-CoV-2 in March 2020, a dramatic decline was observed in the number of IMD cases. This trend continued in 2021, when the lowest number of IMD cases ever recorded was seen. For comparison; the years 2015-2018 recorded approx. 40 annual cases, which increased to 56 cases in 2019.

2019 observed a steep increase of group W cases, and this dominance continued in 2020, when 47% of all cases were caused by group W. Since the introduction of restrictions in March 2020, only two group W cases have been recorded; and in 2021, group B was the dominant group. Figure 1 presents IMD by serogroups for the years 2009-2021.

The 2019 annual report on IMD describes the identification of a Danish sub-clone of group W which has been present since 2016 and which has been detected only in Denmark. In 2019, the Danish sub-clone comprised 15 of 23 group W cases. In 2020, eight of the nine group W cases were genotyped, and seven of the eight cases belonged to the Danish sub-clone. In 2020, the sub-clone was recorded in East Jutland (n=2), North Jutland (n=3), West Jutland (n=1) and in the City of Copenhagen (n=1). All cases were sporadic and no outbreaks with the Danish sub-clone have been recorded. 2020 and 2021 recorded two additional IMD cases caused by group W. It was possible to genotype the case from 2021, and the case belonged to the Danish sub-clone.


In nine of the cases, the diagnosis was made by laboratory verification (culture or PCR). It was possible to group all these cases, as the analysis is conducted at Statens Serum Institut on both isolates and on samples that are only PCR positive. Additionally, in one case, the diagnosis was made based on the clinical picture alone.

Underlying diseases and predispositions

Underlying diseases/predispositions and sequelae were established by linking the civil registration numbers (CPR) recorded during the IMD surveillance to data from the National Patient Registry.

These conditions were categorised into groups based on diagnosis codes. Infections were included as from one month prior to the current IMD case, but no time restrictions were applied for the remaining underlying diseases/predispositions. In five (50%) of the 10 IMD cases recorded in 2021, one or more underlying diseases and/or predispositions were recorded. One child and all persons in the 40+ age group had underlying conditions, whereof pulmonary conditions was the most frequently observed type of condition, followed by cardiovascular diseases and endocrine disorders. The table summarising underlying conditions has not been included in this annual report because of the limited number of IMD cases, but it may be handed out on request provided this can be done in pursuance of data protection regulations.

Mortality and sequelae

One patient died due to IMD in 2021.

Sequelae to IMD were recorded in one patient in 2021 in the form of abnormal involuntary movements.

This annual report is also described in EPI-NEWS no. 40-41/2022.