Meningitis is an infection that causes inflammation of the protective membranes covering the brain and spinal cord.

The inflammation can result from three types of infectious agents, bacteria, viruses, or fungi. Sometimes, the diseases can be the result of noninfectious agents that include chemical reactions, drug allergies, some types of cancer and inflammatory diseases, such as systemic lupus erythematosus.

Several risk factors, such as age, can increases the chance of developing meningitis, but people with a weakened immune system are at the highest risk.

When the infected agent finds its way to the brain, the blood-brain barrier is disrupted and infection-fighting particles start to enter the meninges and brain, leading to swelling.

The common symptoms of meningitis include fever, headache, and stiff neck. other symptoms may appear, including nausea, vomiting, sensitivity to light, and confusion. Newborns and infants who have meningitis may not show the previously mentioned symptoms, as they may suffer from irritability, vomiting, loss of appetite, soft spot on the infant’s head, and abnormal reflexes.

Cases of meningitis can vary from mild to severe. In mild cases, the patient usually recovers within days by following proper treatment, but severe cases can become life-threatening.

Diagnostic tests used to identify meningitis include blood cultures, ultrasound, and spinal tap.

Some forms of meningitis are preventable through vaccines and following good hygiene practices.

Meningitis is spread worldwide. According to the US Centers for Disease Control and Prevention, developing countries have a higher incidence of meningitis than that in developed countries. The African meningitis belt is an area where meningitis breaks in periodic epidemics. 

Meningitis is an inflammation of the meninges, the membranes that surround and protect the brain and spinal cord. Meningitis is usually caused by an infectious agent, bacteria for example, that infects the fluid surrounding the brain and spinal cord and leads to the swelling that causes the symptoms.

There are three common types of meningitis categorized according to the infections agent causing each type. These types are bacterial meningitis, viral meningitis, and fungal meningitis. Noninfectious meningitis is another type that can be caused by the body’s immune reaction to a noninfectious agent, such as certain drugs.

There are three types of organisms that can infect the fluid surrounding the brain and spinal cord and lead to meningitis, followed by bacterial infections and, infrequently, fungal infections.

• Viral meningitis: Viruses are the most common cause of meningitis. Viral meningitis is typically mild and the body can deal with it. Enteroviruses are the most common cause of viral meningitis, but other viruses have been implicated, such as herpes simplex virus, HIV, mumps, West Nile virus and others.
• Bacterial meningitis: This type occurs when invasive bacteria enter the bloodstream and reach the brain and spinal cord, causing acute bacterial meningitis. In some cases, bacterial meningitis occurs when bacteria directly attack the meninges. These direct infections can be caused by an ear or sinus infection, a skull fracture, or, rarely, following some surgeries. The most common strains of bacteria that can cause acute bacterial meningitis include:

1. Streptococcus pneumoniae (pneumococcus): This strain of bacteria usually causes pneumonia or ear or sinus infections, but in some cases it causes meningitis.
2. Neisseria meningitidis (meningococcus): Usually, these bacteria cause an upper respiratory infection, but when they invade the bloodstream, they can cause meningitis. Mainly teenagers and young adults are infected. These bacteria may cause local epidemics in college dormitories, boarding schools and military bases.
3. Haemophilus influenzae (haemophilus): Meningitis in children may result from Haemophilus influenzae type b (Hib) bacterium.

Listeria monocytogenes (listeria): People with a compromised immune system, such as pregnant women, newborns and older adults are more susceptible to listeria infections. Listeria is invasive and can pass the placental barrier.

• Fungal meningitis: Meningitis arising from fungal infectious agents is rare. It can lead to chronic meningitis. Fungal meningitis isn’t transmissible from person to person. The familiar form of fungal meningitis is cryptococcal meningitis, which mainly infects immunocompromised people. If the patient does not receive treatment with antifungal medications, the disease may become life-threatening.

Meningitis can sometimes result from noninfectious causes, such as chemical reactions, drug allergies, some types of cancer and inflammatory diseases, such as sarcoidosis; these can cause an immune response leading to inflammation of the meninges.

Immunocompromised people are at a higher risk of developing any type of infectious meningitis. Other risk factors are divided according to the pathogen:

• Bacterial meningitis:

1. Age: Infants are at high risk for bacterial meningitis compared to people in other age groups.
2. Community settings: Meningitis spreads quickly through large groups by the respiratory route, so people living together in large numbers are at risk.
3. Working with meningitis-causing pathogens: Microbiologists who are exposed to meningitis-causing bacteria are at high risk for developing the disease.
4. Skipping vaccinations: People who did not complete their vaccination schedule are more prone to have meningitis than others.
5. Travelling: People traveling to certain areas may be at a higher risk for meningococcal disease caused by N. meningitidis. These areas include the meningitis belt in sub-Saharan Africa, particularly during the dry season, and Mecca during the annual Hajj and Umrah pilgrimage.

• Viral meningitis:

1. Children under 5 years old

• Fungal meningitis:

1. Premature infants with very low birth weights are at risk of Candida blood stream infection which may spread to the brain.
2. Living in certain areas may increase the risk for fungal lung infections, which can also cause meningitis.

Meninges produce a barrier between the bloodstream and the brain to protect the brain from the body’s immune system. In normal cases this barrier prevents the immune system from attacking the brain. In meningitis, the blood-brain barrier becomes disrupted. When the infected agent finds its way to the brain, the body starts to fight the infection and the blood vessels start to leak fluid, white blood cells, and other infection-fighting particles that enter the meninges and brain. As a result of this process, the brain becomes swelled and blood flow may diminish parts of the brain. In severe cases of bacterial meningitis, the blood-brain barrier is breached, leading to widespread cortical destruction.

Most cases of meningitis are caused by an infectious agent that colonizes or establishes a localized infection in another place in the host. Potential sites of infection include the skin, the nasopharynx, the respiratory tract, the gastrointestinal tract, and the genitourinary tract.  An infectious agent can gain access to the central nervous system and cause meningeal disease via any of the three following major pathways:

• The infectious agent invading the bloodstream of the central nervous system is the most common pathway for most agents. This pathway is characteristic of meningococcal, cryptococcal, syphilitic, and pneumococcal meningitis.

• In rare cases, meningitis may arise from invasion via septic thrombi or osteomyelitic erosion from infected contiguous structures. Meningeal seeding may also occur with a direct bacterial inoculate during trauma, neurosurgery, or instrumentation. Meningitis in the newborn may be transmitted by pathogens that have colonized the maternal intestinal or genital tract, or from nursery personnel or caregivers at home.

• Direct contiguous spread (e.g., sinusitis, otitis media). Local extension from contiguous extracerebral infection is a common cause. Pathogens can follow one of these pathways to migrate from the middle ear to the meninges:

• The bloodstream
• Preformed tissue planes (e.g., posterior fossa)
• Temporal bone fractures
• The oval or round window membranes of the labyrinths

The signs and symptoms of meningitis may include:

• Fever
• Headache
• Stiff neck
• Nausea and Vomiting
• Lack of energy
• Sleepiness
• Increased sensitivity to light
• Altered mental status or confusion

In newborns and infants, the main symptoms of meningitis are absent or not easy to notice.  The infant becomes irritable and may vomit and lose its appetite. In young infants, doctors look for a soft spot on the infant’s head or look for abnormal reflexes.

Doctors analyze the medical history of the patient and perform the following test to diagnose meningitis:

• Physical exam: The doctor will perform a physical exam and check the patient for any signs of infection or inflammation around the ears, the back of the head, and along the spine.
• Blood culture test: This test is performed by monitoring a blood sample for the growth of microorganisms, especially bacteria. The blood sample may also be stained with Gram's stain and then studied under the microscope.

• Head imaging: The doctor may resort to computerized tomography or magnetic resonance scans of the head to detect swelling or inflammation. X-rays or CT scans of the chest or sinuses may also show infection in other areas that may be associated with meningitis. A head ultrasound may be performed on babies younger than six months to detect meningitis because soundwaves can still penetrate fontanel, the soft spot on top of their head.

• Spinal tap (lumbar puncture) test: This test is used for a conclusive diagnosis of meningitis. It is performed by collecting a cerebrospinal fluid sample through a spinal tap. Patients infected with meningitis have low blood glucose levels and increased white blood cell count and protein levels in cerebrospinal fluid.

The treatment of meningitis depends on the cause:

• Bacterial meningitis: This type must be treated as soon as possible to prevent complications including brain swelling and seizures. It is treated by a number of antibiotics and corticosteroids. The exact antibiotics are prescribed according the type of bacteria causing the infection
• Viral meningitis: The majority of viral meningitis cases do not require a specific treatment. Dealing with these cases may only require:

1. Bed rest
2. Drinking plenty of fluids
3. Taking over-the-counter pain medications to reduce fever and relieve body aches

Most cases of viral meningitis resolve within 7 to 10 days. In some cases, corticosteroids are used to decrease swelling in the brain, and anticonvulsants are used to control seizures. If meningitis is caused by the herpes virus, antiviral medication may be used. If the case becomes severe, the patient should be hospitalized.

• Fungal meningitis: Antifungal medications taken intravenously in the hospital are used to treat fungal meningitis. The length of the treatment period depends on the severity of the case, i.e. the strength of the patient’s immune system and the type of fungus causing the infection. Immunocompromised patient’s take longer time to recover than others. As a result of serious side effects of antifungal medications, doctors prefer to delay treatment until a laboratory test confirms that the cause is in fact fungal.
• Noninfectious meningitis: This type is caused by an allergic reaction or an autoimmune disease. Corticosteroids are usually used to treat this type, but, in some cases, no treatment may be required because the condition can resolve on its own.
• Cancer-related meningitis: This type requires treatment for the cancer itself.

Left untreated, meningitis can lead to serious complications due to permanent neurological damage that include:

• Partial or total hearing loss
• Partial or total vision loss
• Multiple seizures
• Memory problems
• Learning difficulties
• Behavioral problems
• Balance and coordination issues
• Gait problems

Other complications related to meningitis may arise from infection spreading in the body. These complications include:

• Kidney problems which may develop to kidney failure.
• Limb amputation to stop the infection from spreading.
• Inflammation in the joints.
• Shock, which is a life-threatening condition when blood flow decreases significantly in the body.

The methods used to prevent meningitis are classified according the cause:

Bacterial meningitis: Vaccination is the most effective method to defend against certain types of bacterial meningitis. People should follow their vaccines schedule. Vaccines that help prevent bacterial meningitis include:

• HIB vaccine
• Pneumococcal conjugate vaccine (PCV13)
• Pneumococcal polysaccharide vaccine (PPSV23)
• Meningococcal conjugate vaccine

Vaccines do not offer a 100% protection against these bacteria, and do not protect against all types of bacteria, so there is still a chance to develop bacterial meningitis even with vaccination. Maintaining good health practices may help in preventing bacterial meningitis, these practices include:

• Stopping smoking and avoiding cigarette smoke because it negatively effects the immune system.
• Avoiding close contact with people who have the disease.
• Getting sufficient rest. 

Pregnant women in 35 to 37 weeks of pregnancy should get tested for group B Streptococcus test; if the test result is positive, the pregnant woman must take antibiotics during labor in order to prevent group B Streptococcus from passing to their newborn. To reduce the risk of meningitis caused by Listeria monocytogenes, pregnant women should avoid certain foods, including:

• Soft cheeses made with unpasteurized milk
• row Sprouts
• Melons
• Cold cut meats.
• smoked sea food

Viral meningitis:  Vaccinations are available for some diseases that can lead to viral meningitis, such as measles, mumps, chickenpox, and influenza. Vaccination are not available for non-polio enteroviruses, which are the most common cause of viral meningitis. Following good hygienic practices are helpful in decreasing the probability of getting infected with non-polio enteroviruses, these practices include:

1. Frequent hand washing with soap and water.
2. Refraining from touching the face with unwashed hands.
3. Keeping away from close contact such as kissing, hugging, or sharing cups or eating utensils with people who are sick.
4. Using a tissue or upper shirt sleeve, not the hands, to cover coughs and sneezes.
5. Taking measures to avoid mosquito and other insect bites that may carry the diseases and infect humans.
6. Cleaning and disinfecting frequently touched surfaces.

- Fungal meningitis: There’s no specific measure to protect against fungal meningitis, but keeping away from soil and other environments that are likely to contain fungus may help reduce the chance. Immunocompromised people should try to avoid bird droppings and avoid digging, particularly if they live in a geographic region where fungi like Histoplasma, Coccidioides, or Blastomyces exist.

Patients with meningitis who have a decreased level of consciousness or have seizures accompanying the disease, especially if seizures extend for a long period of time or are difficult to control, are at higher risk for neurologic disability or death.

In bacterial meningitis, different risk factors are related with the prognosis of patient status. These factors include the following variables related to a bad clinical outcome:

• Old age
• High heart pulse
• Lower Glasgow Coma Scale score
• Cranial nerve palsies
• Cerebrospinal Fluid Analysis leukocyte count less than 1000/μL
• Gram-positive cocci on CSF Gram stain

Half of all patients with bacterial meningitis develop several complications within days to weeks after infection happens; these complications can lead to brain damage, coma, and death.

In viral meningitis, patients usually recover within 7 to 10 days on their own.

According to the Centers for Disease Control and Prevention, developing countries have a higher incidence of meningitis than that in developed countries.  

The African meningitis belt is an area that extends from Senegal to Ethiopia where meningitis occurs in periodic epidemics. One reason for this is that developing countries have less access to preventive measures, such as vaccination.

The World Health Organization reports that 900,000 cases of meningitis occurred in the 26 countries along the African meningitis belt between 1995 and 2014. According to the organization, 10% of these cases were fatal, while 10-20% resulted in lasting neurological complications.