What's the difference between bacterial and viral meningitis?

June 2019

Meningitis can be a very scary word for people to hear. It is important to know that there are different types of meningitis. The different types have different implications in terms of treatment and the risk of passing it on, as well as what the outcome for the patient might be.

Meningitis means inflammation of the meninges (meninges is the medical term for lining of the brain). Inflammation of the meninges, or meningitis, is most often caused by an infection, but can be caused by other things such as medications or other medical conditions.

Meningitis that is caused by an infection is normally caused by either a bacteria or a virus. This blog will explain the main differences between the two.

What is viral meningitis?
 
Viral meningitis is the most common type of meningitis in adults and older children. It can be caused by many different viruses, but the most common are the herpes simplex virus (normally the same type of virus that causes genital herpes), the chickenpox or shingles virus (also known as varicella zoster virus), and the enterovirus. Out of these, enteroviruses are the most common. The MRF fact sheet on viral meningitis provides more information about these different types.
 
Viral meningitis presents with similar symptoms to bacterial meningitis such as fever, headache, dislike of lights and neck stiffness. It can present with a rash, but this is normally quite different to the rash seen in bacterial meningitis with meningococcal disease.
 
Viral meningitis is almost never life-threatening.
 
What is bacterial meningitis?
 
Bacterial meningitis is less common than viral, but it can still happen to anyone of any age. Many different bacteria can cause meningitis but the most common worldwide are meningococcal, pneumoccocal, Haemophilus influenzae. Bacterial meningitis can occur alongside sepsis, which is the more life threatening form of the disease and often involves the bacteria invading the blood as well. Sepsis can occur with or without bacterial meningitis.

Bacterial meningitis and sepsis are serious, life threatening illnesses. The first symptoms are often non-specific and include fever, vomiting, headache and feeling unwell. Limb pain, pale skin, and cold hands and feet often appear earlier than the rash, neck stiffness, dislike of bright lights and confusion.

An image of the meningococcal bacteria, which is the leading cause of bacterial meningitis in the UK and Ireland.
 
How can you tell the difference between viral and bacterial meningitis?
 
To determine whether a person is suffering from viral or bacterial meningitis, doctors will have to perform a lumbar puncture. This involves collecting a sample of the cerebrospinal fluid (CSF) that surrounds the brain and spinal cord to find out what is causing the meningitis. If the results of the lumbar puncture identify a specific virus or bacteria then the diagnosis is clear. Often, however, the specific bug is not identified and the doctor will need to rely on several ‘clues’ in the CSF to decide. If they are unsure they will normally opt to treat for bacterial meningitis, ‘just in case’.

The clues that the doctor uses are the levels of white cells, protein and glucose in the CSF. Typically in bacterial meningitis the white cell count is much higher than in viral meningitis (and is a different type of white cell), the protein is much higher and the glucose is much lower than in viral meningitis.

It is important to know whether the cause is viral or bacterial as this will determine how to treat the patient. In bacterial meningitis antibiotics are essential but in viral meningitis antibiotics will not have any effect. Unfortunately there are no proven treatments for viral meningitis, however, sometimes a doctor might give a drug called Aciclovir which has been shown to be of benefit in other conditions caused by the herpes simplex virus or the chickenpox virus.

Patients with viral meningitis may feel quite unwell for a while after the illness, with symptoms of fatigues, headache and anxiety. However, viral meningitis almost never kills people.  Bacterial meningitis on the other hand can be rapidly fatal or cause devastating after effects, so it is important to treat these cases with antibiotics as soon as possible.
 
Viral meningitis is not passed on to others by being in close contact – unlike the meningococcal form of bacterial meningitis – so no preventive treatment is needed for relatives.

What should I do if I think I have meningitis?
 
If you suspect that you, or someone you know, might be suffering from meningitis it is important to seek medical attention as soon as possible. Trust your instincts and don’t be afraid to seek a second opinion.
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About the author

Dr Fiona McGill
Academic Clinical Lecturer

Dr Fiona McGill works at the Institute of Infection and Global Health at the University of Liverpool.

Learn more by visiting https://www.liverpool.ac.uk/infection-and-global-health/staff/fiona-mcgill/.

Tel: +44 (0)151 795 9649

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