Bacterial Meningitis In Adults

Introduction

Meningitis is an infection of the protective membrane covering the brain and the spinal cord called the meninges. Meningitis can cause a constellation of symptoms in adults and can be potentially life-threatening. These infections can be caused by bacteria, viruses, fungi, or parasites. However, in this article, we will be focusing specifically on bacterial infections causing meningitis.  

It is important to know how to recognise and treat meningitis because it can be potentially life-threatening. If there is any suspicion of meningitis, immediate medical care should be sought out. This is because of the infection's close proximity to the brain and spinal cord. In 2019, there were 2.51 million worldwide cases of meningitis, which led to 236,000 deaths.¹ The number of fatal cases of the condition has dropped over the last 20 years, largely due to better treatment and vaccination.  

In this article, we will look closer at the causes of bacterial meningitis, how it presents in adults, how it is diagnosed, and treatment and prevention of the condition. 

Understanding bacterial meningitis

When the protective layer of the three membranes covering the brain and spinal cord become inflamed, often due to infection, we call it meningitis. Within these layers is a clear-coloured fluid called the cerebrospinal fluid (CSF). Together, the meninges and CSF serve the purpose of protecting the central nervous system, as well as transporting important nutrients to the brain. Infections of the meninges are often transported through this fluid. 

These infections are most commonly caused by viruses but can also be caused by bacteria.² Although less common, bacterial meningitis is more deadly and requires urgent medical attention. It can be difficult to distinguish between the two types of meningitis based on symptoms. The definitive way to know which microorganism is causing the infection is to look at a sample of cerebrospinal fluid under a microscope. 

Many different bacteria can cause meningitis. Here are some of the most common causes:³

• Neisseria meningitidis – the most common cause in adults
• Group B streptococcus – the most common cause in neonates less than 3 months old
• Escherichia coli – another common cause in neonates
• Streptococcus pneumoniae – a common cause in infants less than 10 years old

Symptoms of bacterial meningitis in adults

It is difficult to distinguish between the different types of meningitis based solely on symptoms. The symptoms listed below are similar for all types of meningitis. 

Meningitis can often present similarly to the flu in the early stages. Common symptoms of meningitis may include: 

• Severe headache
• Neck stiffness
• High fever
• Increased sensitivity to light (photophobia)
• Intolerance to loud noises (phonophobia)
• Confusion
• Rash which is ‘non-blanching’ – it does not disappear when pressed with a glass tumbler 

Meningitis presents slightly differently in small children younger than two: 

• High fever
• More irritable than usual 
• Increasingly sleepy 
• Inactive or sluggish 
• Constant crying 
• Poor feeding and vomiting 
• The soft spot on the top of their head bulging
• Stiffness throughout the body. 

Symptoms of meningitis can progress rapidly. If left untreated, the infection can travel into the bloodstream (also known as sepsis) and cause a widespread inflammatory response throughout the body, causing a fall in blood pressure, fast heart rate, and rapid breathing.⁴ As the infection is primarily located around the brain, it can cause a swelling of the brain which increases the pressure in the skull (known as hydrocephalus).⁵ This may reduce a person’s level of consciousness and cause seizures. Meningitis can also increase the likelihood of blood clots forming around the body (known as disseminated intravascular coagulation).

Diagnosis of bacterial meningitis in adults

Symptoms give a clear indication of a diagnosis of meningitis but cannot however conclusively diagnose the condition. Equally, there are no diagnostic physical tests. 

There are several laboratory tests doctors may perform to diagnose meningitis. They may take samples of blood which could show elevated infection markers. They may also take blood cultures to try to sample and grow the bacteria which may be causing the infection. 

However, the most important test for diagnosis is examining a sample of cerebrospinal fluid (CSF). This is obtained through a procedure called a lumbar puncture, whereby a small needle will be used to obtain a sample of spinal fluid from the base of the back. Analysis of CSF will clearly be able to differentiate between different types of meningitis and diagnose bacterial meningitis. 

Imaging of the brain such as CT or MRI may be used at a later stage to look for complications of meningitis. 

Treatment of bacterial meningitis

Anyone with a suspected diagnosis of meningitis should be hospitalised for further investigations. These patients are then often isolated within the hospital, to prevent the spread of infectious diseases to other patients. 

The main treatment of bacterial meningitis is antibiotics. These should be given as soon as the diagnosis is suspected without any delay.⁶ This includes giving them before further tests previously described such as a lumbar puncture. These are given with fluids through a drip to keep the person hydrated. Steroids may also be given in some cases where there is suspected swelling of the brain. 

Prevention of bacterial meningitis in adults

Vaccinations exist against some of the common causes of bacterial meningitis. In the UK, the common strains vaccinated against are:⁷ 

• Haemophilus influenzae – children vaccinated in 4 doses at 8, 12, 16 weeks, and 1 year old
• Meningococcal group B bacteria – children vaccinated in 3 doses at 8 weeks, 16 weeks, and 1 year old
• Pneumococcus – children vaccinated in 2 doses at 12 weeks and 1 year old
• Meningococcal group C bacteria – children vaccinated in 1 dose at 1 year old
• Meningococcal groups A, C, W and Y – teenagers vaccinated in 1 dose at 14 years old

Prophylaxis 

In some cases, doctors may recommend treatment for those who have come into contact with someone who has bacterial meningitis. This will often be in the form of tablet antibiotics. This is called prophylaxis. It is particularly important for those people with underlying health conditions, or those people with weakened immune systems. 

Conclusion

Meningitis is a serious infection of the meninges, the protective layer surrounding the brain and spinal cord. It can affect people of all ages and can be caused by many different microorganisms, including bacteria. It causes a range of symptoms – the most common being headaches, neck stiffness and high temperature. Early recognition and treatment of the condition is important for good outcomes.