Meningitis and Encephalitis: Infection Around or Within the Brain

Meningitis is inflammation of the protective layers around the brain and spinal cord. Encephalitis is inflammation of brain tissue itself. Both can become life threatening quickly, and their early features may resemble less serious infections.

Two different sites of inflammation The brain and spinal cord form the central nervous system. They are covered by protective layers called the meninges. Meningitis means inflammation of these protective layers and the fluid filled spaces around them. Infection is a common cause, although inflammation can occasionally have another cause. Encephalitis means inflammation within the brain tissue itself. Viruses are important causes, but encephalitis can also result from the immune system mistakenly attacking the brain. This lesson focuses mainly on infectious encephalitis because it belongs within the Infection and Immunity module. Autoimmune encephalitis is not caused by an organism, even though its presentation can overlap with infection. Meningitis and encephalitis can occur together. Clinicians may use the term meningoencephalitis when both the meninges and brain tissue appear to be involved. Why the distinction matters Inflamed meninges commonly produce headache, neck discomfort, vomiting and sensitivity to bright light. Inflammation within brain tissue is more likely to alter brain function directly. Encephalitis may cause confusion, unusual behaviour, personality change, speech difficulty, seizures, hallucinations or weakness affecting part of the body. These features can also occur during severe meningitis, so symptoms do not always separate the conditions cleanly. Both illnesses can increase pressure within the skull, provoke seizures and disrupt consciousness. They require urgent hospital assessment because deterioration can occur over hours. A person does not need to have every recognised feature. The pattern also differs between babies, children, adults and older people. What causes meningitis Bacteria and viruses are the most common infectious causes of meningitis in the UK. Fungi, tuberculosis bacteria and other organisms cause a smaller proportion of cases. Bacterial meningitis is generally more likely than viral meningitis to cause rapid deterioration, death or lasting complications. It requires immediate intravenous antibiotics. Many cases of viral meningitis are less severe and improve with supportive care. However, bacterial and viral meningitis cannot be reliably distinguished at home from symptoms alone. Different organisms are more likely at different ages and in different clinical circumstances. Vaccination, immune function, recent surgery and anatomical problems can also alter risk. What causes encephalitis Encephalitis is often caused by a virus. Herpes simplex virus and varicella zoster virus are important treatable causes, although encephalitis remains a rare complication of these common infections. Other viral causes include enteroviruses and viruses associated with measles, mumps or rubella. Some viruses are transmitted by mosquitoes, ticks or infected mammals, usually in particular geographical settings. Bacteria, fungi and parasites cause encephalitis less often. In many people, the exact cause is not identified despite appropriate testing. Autoimmune encephalitis develops when the immune system attacks proteins within the brain. It may follow an infection, occur with a tumour or develop without a clear trigger. Encephalitis itself is not normally passed from one person to another. However, an infection capable of causing encephalitis may sometimes spread between people. Meningococcal disease is not the same as all meningitis Meningococcal disease is caused by the bacterium Neisseria meningitidis. It can cause meningitis, meningococcal sepsis, or both at the same time. Meningococcal sepsis occurs when invasive infection affects the bloodstream and circulation. It can progress rapidly even without obvious signs of meningitis. Other bacteria can also cause meningitis, including pneumococcal bacteria and Haemophilus influenzae type b. A person can therefore have bacterial meningitis without having meningococcal disease. Meningococcal bacteria can be carried harmlessly in the nose or throat. Transmission usually requires close or prolonged contact, rather than simply passing someone briefly. The non blanching rash and its limitations Meningococcal disease can cause red or purple spots where bleeding occurs beneath the skin. These spots may not fade when pressed firmly with the side of a clear glass. A rapidly spreading non blanching rash or larger purple areas is an emergency. The person may have meningococcal sepsis with or without meningitis. The absence of a rash does not exclude meningococcal disease. A rash may never develop, may appear late or may initially fade before becoming non blanching. Do not wait for a rash before seeking emergency help. The glass test does not rule out meningitis or encephalitis and should never delay calling 999. Rashes can be harder to see on brown, black or tanned skin. Check the whole body, including nappy areas, palms, soles, inside the eyelids and the roof of the mouth. The recognised meningitis pattern Fever, headache, neck stiffness and altered consciousness together form an important red flag combination for bacterial meningitis. Altered consciousness includes confusion, delirium, unusual drowsiness or reduced responsiveness. Having all four features makes bacterial meningitis particularly concerning. However, NICE states that bacterial meningitis may still be strongly suspected when the full combination is absent. Other possible features include vomiting, photophobia, seizures, limb or body pain, irritability and an ill appearance. A person may have a very high temperature, a low temperature or no recorded fever. Fever and neck stiffness are less common in babies. Fever can also be less prominent in older adults, while arthritis, dementia or communication difficulties may make neck stiffness or headache harder to identify. Young adults with confusion or unusual behaviour may mistakenly be assumed to have used alcohol or drugs. A sudden change still requires medical assessment. Babies and young children may look different Babies cannot describe headache, neck stiffness or sensitivity to light. Their illness may first appear as a change from their normal behaviour. Possible features include reduced feeding, repeated vomiting, unusual irritability, lethargy or difficulty waking. A baby may become floppy, unusually stiff or poorly responsive. A weak, high pitched or continuous cry can be concerning. The soft spot on the head, called the fontanelle, may bulge, although this sign is not always present. Breathing may become rapid or irregular. Grunting, pauses in breathing, pale or mottled colour, cold hands and feet, reduced urine and delayed capillary refill can suggest severe illness or meningococcal sepsis. Seizures, focal weakness and reduced consciousness raise concern about meningitis, encephalitis or another neurological emergency. Classic signs may be absent, especially in young babies. Parent or carer concern matters. Someone who knows the child may notice that feeding, crying, movement or interaction is markedly different from usual. Encephalitis affects how the brain works Encephalitis may begin with fever, headache, nausea and muscle aches. Sometimes the first recognised features are neurological or behavioural. New confusion, disorientation, marked drowsiness or loss of consciousness can occur. Some people develop agitation, personality change, hallucinations or behaviour that appears psychiatric. Seizures may involve the whole body or begin in one part. Focal neurological signs include weakness on one side, speech difficulty, loss of sensation or abnormal movements. These features are not specific to encephalitis. Stroke, metabolic disturbances, poisoning, epilepsy, brain tumours, meningitis and several other illnesses can produce similar changes. The combination of fever or recent infection with altered brain function raises concern, but diagnosis requires hospital investigation. Who is more vulnerable Meningitis and encephalitis can affect anyone. Babies, young children and older adults have a greater risk of severe illness or an atypical presentation. Teenagers and young adults have an increased risk of meningococcal disease, particularly when living in large shared accommodation. Close contact can facilitate transmission among people carrying meningococcal bacteria. Risk also increases with weakened immune function, reduced or absent spleen function and certain complement disorders. Missing relevant vaccines leaves a person without protection those vaccines would otherwise provide. A cerebrospinal fluid leak, cochlear implant, recent neurosurgery or previous meningitis can increase the risk of bacterial meningitis. These factors do not establish the diagnosis by themselves. Travel and environmental exposure can change the possible infectious causes. Clinicians may ask about mosquito or tick bites, animal exposure and recent travel. How clinicians assess suspected disease Assessment begins with immediate attention to the airway, breathing, circulation, consciousness and seizures. Clinicians also look for sepsis, shock and raised pressure within the skull. They ask how quickly symptoms developed and whether there was fever, headache, vomiting, neck discomfort, rash, unusual behaviour or a seizure. Family members may provide essential information about recent changes. The examination includes vital signs, alertness, pupils, limb strength and other neurological functions. The clinician checks the whole skin surface for petechiae or purpura and examines babies for feeding, tone and fontanelle changes. Meningitis, encephalitis and meningococcal sepsis overlap with many other emergencies. The first assessment therefore addresses immediate danger while keeping several possible diagnoses open. Blood tests, lumbar puncture and brain tests There is no single bedside test that immediately confirms or excludes meningitis or encephalitis. Hospital investigations are interpreted together with the clinical pattern. Blood tests may include cultures, blood cell counts, inflammatory markers, glucose and polymerase chain reaction tests. Normal inflammatory markers or a normal white cell count do not exclude bacterial meningitis. A lumbar puncture removes a sample of cerebrospinal fluid from the lower back. The fluid can be examined for inflammatory cells, protein, glucose, bacteria and genetic material from infectious organisms. Lumbar puncture is performed before antibiotics when it is safe and does not cause a clinically significant delay. Antibiotic treatment must not wait when the procedure is unsafe or would delay urgent care. Brain imaging is not required routinely before every lumbar puncture. CT or MRI may be needed first when focal neurological signs, abnormal pupils, severely reduced consciousness or another feature raises concern about pressure or a space occupying problem. MRI can support the diagnosis of encephalitis and show patterns of brain inflammation. An electroencephalogram records electrical activity and may identify seizures or other abnormal brain activity. No scan, blood result, cerebrospinal fluid value or electrical recording answers every diagnostic question alone. Early results may need repeating or reinterpreting as the illness develops. Emergency treatment principles Suspected bacterial meningitis or meningococcal disease requires emergency transfer to hospital. NICE recommends starting intravenous antibiotics within one hour of arrival when bacterial meningitis is suspected. Blood samples and a lumbar puncture are obtained first when this is safe and does not create a significant delay. Treatment proceeds immediately when diagnostic procedures cannot be completed safely. People older than three months with strongly suspected or confirmed bacterial meningitis are usually given intravenous dexamethasone with or close to the first antibiotic dose. Antibiotics are not delayed while waiting for dexamethasone. Strongly suspected herpes simplex encephalitis is treated with intravenous aciclovir. Antiviral treatment is not given routinely for every suspected meningitis case because it only benefits particular viral causes. Other care may include oxygen, intravenous fluids, seizure treatment, respiratory support and intensive care. Autoimmune encephalitis may require medicines that suppress or modify the immune response. Treatment is refined when cultures, PCR results, scans and the clinical course provide more information. Specialist infection, neurological, paediatric or critical care teams may be involved. Public health action after meningococcal disease Suspected meningococcal disease triggers urgent public health involvement. UKHSA works with the treating team to identify people who meet the definition of a close contact. Selected close contacts are offered preventive antibiotics to clear meningococcal carriage and reduce further transmission. Vaccination may also be recommended in defined circumstances. Not everyone who attended the same school, workplace or event automatically needs antibiotics. Public health teams assess the nature and duration of contact. Preventive antibiotics do not replace symptom awareness. A close contact who becomes unwell still needs urgent assessment even after taking prophylaxis. Recovery and possible lasting effects Many people recover from meningitis, especially when treatment begins promptly. Recovery depends on the organism, severity, age, complications and speed of treatment. Bacterial meningitis can cause hearing loss, seizures, weakness, cognitive difficulty and developmental or learning problems. Meningococcal sepsis can also damage skin, limbs, kidneys and other organs. Encephalitis may cause persistent problems with memory, personality, language, swallowing, mood, concentration, balance or movement. Some people develop epilepsy or prolonged fatigue. Recovery from encephalitis can take months or longer. Rehabilitation may involve neurology, physiotherapy, occupational therapy, speech and language therapy, psychology and educational support. Follow up after bacterial meningitis or meningococcal disease includes assessment for hearing, neurological and developmental complications. Some difficulties become apparent only when a child reaches a new educational stage. Vaccination reduces but does not remove risk The UK vaccination programme protects against several important causes of meningitis. These include meningococcal, pneumococcal, Haemophilus influenzae type b, measles and mumps infections. No vaccine prevents every type of meningitis or encephalitis. A vaccinated person with concerning symptoms still needs emergency assessment. Additional vaccines may be recommended for particular medical conditions, travel destinations or outbreaks. Current NHS and UKHSA advice should be followed because schedules and eligibility can change. What this lesson should not be used for This lesson explains two serious forms of central nervous system inflammation. It cannot determine the cause of headache, fever, confusion or a rash at home. Do not wait for neck stiffness, a rash or every classic symptom. Suspected meningitis or encephalitis requires emergency assessment rather than home monitoring or an online score.

Meningitis affects the protective meninges around the brain and spinal cord, while encephalitis affects brain tissue itself. Both are medical emergencies when suspected. A non blanching rash is an important meningococcal warning sign, but its absence never excludes meningococcal disease or bacterial meningitis.