Bacterial meningitis: Aetiology, risk factors, disease trends and severe sequelae during 50 years in Sweden

Background Bacterial meningitis (BM) is a rare but severe infection. Few population-based studies have characterised BM episodes and sequelae over long periods. Methods This was a population-based observational cohort study with national coverage, using data on aetiological pathogens, sex, premorbid conditions, steroid pretreatment, severe sequelae and birth, death and diagnosis dates collected from 10,339 patients with BM reported to the National Board of Health and Welfare in Sweden between 1964 and 2014. Results During the 50-year study period, the incidence of BM decreased in young children, but not in the elderly. The most common cause of BM was pneumococci (34%), followed by Haemophilus influenzae (26%), and meningococci (18%), mainly community acquired. Premorbid conditions were found in 20%. After the H. influenzae type b vaccine was introduced in 1993, the BM incidence decreased by 36%. Following pneumococcal conjugated vaccine introduction in 2009, the incidence and 30-day mortality from pneumococcal meningitis decreased by 64% and 100%, respectively, in previously healthy children, and the 30-day mortality decreased by 64% among comorbid adults. The BM incidence in immunosuppressed patients increased by 3% annually post vaccine introduction. The 30-day mortality was 3% in children and 14% in adults, and the rate of severe sequelae was 44%. On average, patients lost 11 years of healthy life due to BM. Conclusion The introduction of conjugated vaccines into the childhood vaccination program has reduced the incidence of BM in young children, but not in adults. Post vaccine introduction, patients present with more premorbid conditions and other bacterial causes of BM, emphasising the need for a correct diagnosis when treating these infections.

Automated summary

This study conducted a 50-year investigation on the epidemiology of bacterial meningitis in Sweden and found that the incidence rate in children decreased while it remained unchanged in adults. The main pathogens were Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis. The introduction of vaccines led to a decrease in incidence and mortality in previously healthy children, but an increase in immunosuppressed patients. The study highlights the importance of correct diagnosis when treating these infections.