Infectious meningitis and encephalitis in adults in Denmark: A prospective nationwide observational cohort study (DASGIB)

OBJECTIVES: To monitor epidemiological trends of infectious meningitis (bacterial and viral) and encephalitis in Denmark.

METHODS: Nation-wide prospective observational study of all cases with proven community-acquired infectious meningitis and encephalitis in adults treated in all departments of infectious diseases in Denmark from 1st of January 2015 to 30th of June 2016. We included data on symptoms, aetiology, treatment and outcome assessed by the Glasgow Outcome Scale (GOS) 30-days after discharge. GOS 1-4 was categorised as unfavourable outcome.

RESULTS: During 18 months of observation, we identified 252 cases of viral meningitis (3.6/100,000/year), 214 cases of bacterial meningitis (3.1/100,000/year), and 96 cases of infectious encephalitis (1.4/100,000/year). In bacterial meningitis, Streptococcus pneumoniae was most frequent (n=101) followed by Staphylococcus aureus (n=24) and β-haemolytic streptococci (n=14). Meningococcal meningitis was rare (n=11). In encephalitis, Herpes simplex virus-1 was most common (n=37) followed by Varicella zoster virus (n=20), while Varicella zoster virus (n=61) was most common in viral meningitis followed by enterovirus (n=50) and Herpes simplex virus-2 (n=46). Case fatality and unfavourable outcome occurred in 31/214 (15%) and 96/214 (45%) with bacterial meningitis and in 5/96 (5%) and 55/89 (62%) with encephalitis. For viral meningitis, unfavourable outcome occurred in 41/252 (17%).

CONCLUSIONS: The epidemiology and clinical presentation of the examined central nervous system (CNS) infections differed considerably and bacterial meningitis was more frequent than previously estimated. Overall prognosis remains poor for bacterial meningitis and encephalitis. Prospective nationwide clinical databases of CNS infections may be superior to epidemiological monitoring based on notifications or laboratory systems.