What are the causes of meningitis?

From the Guidelines

Meningitis is caused by a variety of infectious agents, including bacteria, viruses, fungi, and parasites, as well as non-infectious triggers, with the most common causes being Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type b for bacterial meningitis, and enteroviruses, herpes simplex virus, and arboviruses for viral meningitis. The causes of meningitis can be broadly categorized into:

• Bacterial meningitis, which is commonly caused by Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type b 1
• Viral meningitis, which is frequently caused by enteroviruses, herpes simplex virus, and arboviruses 1
• Fungal meningitis, which typically affects immunocompromised individuals and is caused by Cryptococcus, Candida, and Histoplasma 1
• Parasitic meningitis, which is rare but can be caused by organisms like Angiostrongylus cantonensis 1
• Non-infectious causes, including certain medications (NSAIDs, antibiotics), autoimmune conditions (lupus, sarcoidosis), and cancers that spread to the meninges 1

The route of infection varies, with pathogens entering through the bloodstream, direct spread from nearby infections like sinusitis or ear infections, or through trauma that allows pathogens to bypass the blood-brain barrier 1. Understanding these diverse causes is essential for proper diagnosis and treatment, as management approaches differ significantly depending on the underlying cause. For example, viral meningitis is often treated supportively with analgesia and fluids, while bacterial meningitis requires prompt antibiotic treatment 1.

Some key considerations for specific demographic groups include:

• Young adults: viral meningitis is more common than bacterial, especially in women in their 20s-40s, and there is a second peak of meningococcal disease in late teens/early 20s 1
• Older adults: pneumococcal disease is more common in over 50s, and Listeria is more common in over 60s but remains rare 1
• Immunocompromised individuals: Cryptococcal meningitis is commonest in those with a CD4 count <100, and TB meningitis is an important consideration at all CD4 counts 1

It is also important to consider the patient's travel history, as certain infections may be more common in specific regions, such as Toscana Virus in the Mediterranean or Tick Borne Encephalitis Virus in Central and Eastern Europe 1.

From the Research

Causes of Meningitis

The causes of meningitis can be categorized into several types, including:

• Bacterial meningitis: caused by bacteria such as Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae 2, 3, 4
• Viral meningitis: caused by viruses such as enteroviruses, herpesviruses, and influenza viruses 5
• Fungal meningitis: caused by fungal infections, although less common than bacterial and viral meningitis 5

Bacterial Meningitis Causes

Bacterial meningitis is caused by several types of bacteria, including:

• Streptococcus pneumoniae 2, 3, 4
• Neisseria meningitidis 2, 3, 4
• Haemophilus influenzae 2, 3, 4
• Streptococcus agalactiae (group B Streptococcus) 4

Viral Meningitis Causes

Viral meningitis is caused by several types of viruses, including:

• Enteroviruses 5
• Herpesviruses 5
• Influenza viruses 5

Other Causes

Other causes of meningitis include fungal infections, although these are less common than bacterial and viral meningitis 5. The exact cause of meningitis can be determined through laboratory tests, such as cerebrospinal fluid (CSF) culture and PCR 3, 6.