Bacterial meningitis is an acute purulent infection of the meninges and subarachnoid space. If the brain parenchyma is also involved in the inflammatory reaction, meningoencephalitis develops.^[1] In adults, the majority of bacterial meningitis in Europe is caused by S. pneumoniae (53%), followed by N. meningitidis (27%). L. monocytogenes (4%) is the third most common cause in adults and is associated with old age and immunosuppression. H. influenzae (3%) in adults has been associated with concomitant conditions such as otitis and sinusitis. Staphylococcus aureus association with meningitis is rare (1-2%).^[2] Bacterial meningitis in children in Europe is due to N. meningitidis (50%), S. pneumoniae (37%), and H. influenzae (5%). In China, the main etiological agent in this age group is S. pneumoniae (33.2%), followed by Escherichia coli (10.9%), Enterococcus spp. (10%), Streptococcus group B (8.2%), S. aureus (4.1%), Pseudomonas aeruginosa (4.1%), Salmonella spp. (3.6%).^[3]

Bacterial meningitis in children usually begins with fever (93%). Headache is registered in 75% of children over 5 years; vomiting in 61%; rash - 60%; neck stiffness - 61%. Seizures occur in 33% of children, alteration in consciousness in 34.5%, and focal neurological deficit in 13.5%.^[4] The most common symptoms associated with the disease in adults are headache, fever, neck stiffness, and changes in consciousness. Data from European studies (1996–2010) show that in adults fever occurs on average in 90% of cases; headache in 77%; vomiting - 60%; rash - 33%; seizures - 22.5%; neck stiffness - 75%, impaired consciousness - 57% (coma - 13%), and focal deficits in 23%.^[5,6] Concomitant diseases occur in 48% of adults, with otitis or sinusitis (25%) and pneumonia (12%) being among the most common.^[7,8]

There are significant differences in the etiological spectrum, clinical presentation and outcome of bacterial meningitis in the age groups, and their recognition is important for early diagnosis and adequate therapy.

The aim of the study was to establish the differences in the etiology and clinical course of bacterial neuroinfections between children and adults.

The study included 90 patients with bacterial neuroinfection admitted to St George University Hospital in Plovdiv from January 1, 2016 to September 31, 2019. There were 25 children (up to 17 years of age) and 65 adults (range 18–87 years). The diagnosis was based on the clinical presentation, cerebrospinal fluid (CSF) examination, and microbiological testing.

Only patients with typical CSF abnormalities consistent with bacterial meningitis were included in the study (cell count >100×10⁶/l, protein >1 g/l, CSF/serum glucose ratio ≤0.4) and/or identified etiology by the CSF microbiological analysis.

We used in the study:

1. Epidemiological data about age and sex;

2. Clinical analysis;

3. Microbiological testing included CSF Gram stain and culture. Multiplex PCR for viral and bacterial agents was performed in 28 of the patients with bacterial neuroinfection. It is based on the detection of specific target genes of the most common causative agents by Biofire FilmArray Multiplex PCR (bioMerieux, France). The panel simultaneously identifies the following bacterial pathogens: S. pneumoniae, Streptococcus agalactiae, N. meningitis, L. monocytogenes, H. influenzae, Escherichia coli K1.

4. Statistical analysis: descriptive methods; parametric and non-parametric methods: Fisher’s exact test and χ²; Kolmogorov-Smirnov test. The significance level of the null hypothesis is p<0.05. Statistical data analysis was performed using the software product SPSS v.17 (IBM, USA).

Streptococcus pneumoniae remains the most common etiologic agent of purulent meningitis in adults, although there has been a reduction in the incidence after the introduction of the pneumococcal vaccines. Unexpectedly high frequency was found for Staphylococcus spp. (18.5%), which according to other studies is quite a rare cause of neuroinfections.^[9–11] This is probably due to a large number of patients with sepsis, in which staphylococcal meningitis followed. Listeria monocytogenes, which is the third leading cause of bacterial neuroinfections in our patients and according to numerous European studies, will be increasingly important in the near future, because of the growing number of people with concomitant oncological and autoimmune diseases and immunosuppression.

Similar to European data^[2,12], the main causative agents of bacterial meningitis in children are Neisseria meningitidis and Streptococcus pneumoniae, but no case of Haemophilus influenzae was observed, in contrast to studies in Poland and Turkey, reporting an incidence of 18%.^[13,14] There is still a high incidence of meningitis due to Haemophilus influenzae in countries with incomplete immunization programs such as Iran and Pakistan (12.4%).^[15,16]

In our study, there is a high proportion of etiologically unidentified neuroinfections (40%). May be due to the fact that a significant proportion of patients were initiated on antibiotic therapy before undergoing a lumbar puncture, that makes it difficult to identify the cause by CSF culture

The distribution of patients by gender showed a male prevalence regardless of age. According to other authors, men and women suffer equally often, with insignificant differences.^[5,17]

The analysis of the clinical presentation showed that fever was the most common symptom (96.7%). While vomiting was more prevalent in children (80% vs. 43.1% in adults), the headache was more common in adults (66.2% vs. 40%). Similar data on the main clinical symptoms have been reported by a number of researchers in Europe.‌^[8,13,18,19] Photophobia had an unexpectedly low frequency (17.8%). Our patients had a skin rash in 24% of children and 15.4% of adults. Many authors reported a significantly higher frequency of rash in both children (39-51%) and adults groups (20-26%).^[17,20-22]

In the observed patients neck stiffness, Kernig and Brudzinski’s signs are more widespread in adults. Seizures are more common in children (24%) than in adults (18.5%). These findings correlate with the data of many European authors.^[6,23-25]

The frequency of cranial nerve palsy in the studied patients (7.8%) was several times lower compared to the data of Van de Beek et al. (28%).^[8] The incidence of focal neurological deficit (10%) is also lower when compared to other European studies, reporting 15–34%.^[17,20,26]

Comorbidities were more common in adults (53.8%) than in children (36%). Weisfelt et al. reported 32.5% for otitis or sinusitis, 15.2% pneumonia, and 13% sepsis, similar to our results.^[6,7] The disease prognosis was more favourable for children. The mortality rate was much higher in adults, which is in accordance with the literature.^[7,16,17]

The most common etiological agents of bacterial agents are Streptococcus pneumoniae in adults, and Neisseria meningitidis and Streptococcus pneumoniae in children. Headache and disturbances in consciousness are more common in adults, while vomiting and ear pain are more typical in children. Because of the high mortality and sequelae in patients with bacterial neuroinfections, rapid clinical recognition and laboratory diagnosis are needed in order to begin adequate treatment as soon as possible.