Bacterial meningitis (BM) is a severe infectious disease, which causes significant morbidity and mortality up to 30%. BM can be classified into community-acquired or nosocomial form. Post-neurosurgical meningitis (PNM), a subtype of nosocomial BM, can occur after neurosurgical operations. PNM prolongs treatment periods and causes significantly more costs. BM causes a substantial health economic burden. The implementation of vaccinations have caused a decrease in the incidence of BM worldwide.

The aim of this thesis was to describe the incidence, characterize the clinical picture, identify the causative bacteria, study the predisposing factors, and define the indicators of unfavorable outcome in pediatric and adult populations with BM.

This thesis consists of three different studies. In the first two studies the medical records of 185 patients diagnosed with BM and in the third 345 patients undergoing glioma surgery in Turku University Hospital, were retrospectively studied between 2011-2018. The included patients had either a cerebrospinal fluid (CSF) culture positive- or negative BM. The outcome was evaluated with Glasgow Outcome Scale, and unfavorable outcome was defined as a score from one to four.

The incidence of BM was slightly higher than previously reported. Streptococcus pneumoniae was the most frequent causative pathogen in children and adults, while Streptococcus agalactiae and Escherichia coli dominated the etiology in infants. Staphylococcus epidermidis was the most frequently found pathogen in PNM patients. The proportion of nosocomial BM was high, and so was the frequency of pre-diagnostic antibiotic use. Headache and administration of pre-diagnostic antibiotics were associated with unfavorable outcome in adult population, and pretermity and nosocomial BM with pediatric population. Repetitive surgeries were risk factors for PNM, and the rate of PNM was higher among low-grade glioma patients compared to patients with high-grade glioma. The frequency of unfavorable outcome of patients was either compatible with previous studies or lower. The management of BM patients is at good international class in Southwestern Finland.