Written by Laura Murphy
This article is a comprehensive review of the epidemiology, pathophysiology, presentation, diagnosis, treatment, and complications of community-acquired bacterial meningitis.
Why does this matter?
Bacterial meningitis is a highly morbid disease. Prompt recognition and treatment is essential to improve patient outcomes. The article is worth a read in its entirety, but some of the key points are summarized below.
Bacteria on the brain
Epidemiology: Conjugate vaccines against the three most common pathogens (Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae) have reduced the incidence of bacterial meningitis, but the emergence of non-vaccine serotypes and antimicrobial resistance continues to pose a challenge. Furthermore, the burden of disease varies substantially based on geographical region, with a strong association with poverty. The incidence is 0.9 per 100,000 in high-income countries, but it is much higher in low and middle-income countries with dense populations (20-80 cases per 100,000) and highest in the Sahel region in west/central Africa (1,000 cases per 100,000).
Diagnosis: The classic triad of neck stiffness, fever, and altered mental status is present in only 40-50% of patients with bacterial meningitis. The gold standard for diagnosis is CSF culture, which returns positive in 85% of cases. Other findings include decreased CSF glucose and elevated protein levels, CSF WBC and neutrophil counts as well as elevated opening pressure. PCR testing can be used to identify specific pathogens more rapidly. CSF lactate can help to discriminate bacterial meningitis from aseptic meningitis. Blood cultures are positive in 75% of cases. Neuroimaging should be obtained prior to lumbar puncture in patients with concern for space-occupying lesion (e.g. new-onset seizure, focal neurologic deficit, immunocompromise, or impaired consciousness). However, this is a known risk factor for delayed antibiotic treatment and poor disease outcomes, so be sure to initiate treatment prior to CT imaging.
Treatment: Empiric antimicrobial treatment should be initiated as soon as possible, ideally within 1 hour, and should be targeted at the most likely pathogens. Adjunctive dexamethasone therapy is recommended in patients with bacterial meningitis beyond the neonatal period in countries with high levels of medical care, as it has been shown to decrease complications due to S. pneumoniae. See summary table below for recommended agents.
Complications: Patients are at risk for hearing loss, hydrocephalus, seizures and cerebrovascular complications such as stroke, cerebral venous thrombosis, and intracerebral hemorrhage. Imaging should be obtained in patients with a decline in mental status or who fail to improve within 48 h after appropriate antibiotic therapy. Co-existing septic shock is a predictor for poor outcome.
Community-acquired bacterial meningitis. Lancet. 2021 Sep 25;398(10306):1171-1183. doi: 10.1016/S0140-6736(21)00883-7. Epub 2021 Jul 22.
WHO roadmap toward defeating meningitis by 2030