brain, spinal cord, and nerve disorders
Acute Bacterial Meningitis
Causes of Acute Bacterial Meningitis
Different species of bacteria can cause meningitis. The bacteria most likely to be the cause depends on How old people are How they acquired meningitis (the route) How strong their immune system is Acute bacterial meningitis can develop in infants and children, particularly in geographic areas where children are not vaccinated. As people age, acute bacterial meningitis becomes more common. Innewborns and young infants,the most common causes of bacterial meningitis are Group B streptococci, particularlyStreptococcus agalactiae and related bacteria (called Overview of Gram-Negative Bacteria ) Listeria monocytogenes If meningitis develops within the first 48 hours after birth, it is usually acquired from the mother. It may be transmitted from mother to newborn as the newborn passes through the birth canal. In these cases, meningitis is often part of a serious bloodstream infection ( Sepsis and Septic Shock ). Inolder infants, children, and young adults,the most common causes are (also called Meningococcal Infections ) (also called Pneumococcal Infections ) Neisseria meningitidisoccasionally causes a rapid, severe infection called meningococcal meningitis, resulting in coma and death within hours. This infection commonly occurs when bacteria from an upper respiratory infection enter the bloodstream. Meningococcal meningitis is highly contagious. Small epidemics of meningococcal meningitis may occur among people living in close quarters, as occurs in military barracks and college dormitories.Neisseria meningitidisbecomes less common as people age. Haemophilus influenzaetype B is now a rare cause of meningitis in the United States and Western Europe because most children are vaccinated against this bacteria. However, in areas where the vaccine is not widely used, these bacteria are a common cause, particularly in children aged 2 months to 6 years. Inmiddle-aged and older adults,the most common cause is Streptococcus pneumoniae As people age,the immune system weakens, increasing their risk of meningitis due to other bacteria, such asListeria monocytogenes,E. coli, or other gram-negative bacteria. Inpeople of all ages,Staphylococcus aureusoccasionally causes severe meningitis. Bacterial meningitis can be acquired in different ways, including When the bacteria spread through the bloodstream from an infection in another part of the body (the most common route) When bacteria spread to the meninges from another infection in the head, such as sinusitis or an ear infection (often caused byStreptococcus pneumoniae) After a wound penetrates the skull or meninges (often caused byStaphylococcus aureus) When surgery is done on the brain or spinal cord (often caused by gram-negative bacteria) When a drain (shunt), placed in the brain to relieve increased pressure in the skull, becomes infected When bacteria enter through a birth defect in the skull or spine (such as Neural Tube Defects and Spina Bifida ) Having any of the above conditions increases the risk of developing bacterial meningitis. Which bacteria are likely to cause meningitis depends on whether the immune system is normal or weakened. Conditions that can weaken the immune system increase the risk of developing bacterial meningitis. Such conditions include Treatment with corticosteroids or other drugs that suppress the immune system ( Secondary immunodeficiency disorders ), which are used to treat autoimmune disorders and cancer or to prevent rejection of a transplanted organ Chemotherapy Human Immunodeficiency Virus (HIV) Infection or AIDS Removal of the spleen (splenectomy) Sickle Cell Disease None Primary immunodeficiency (when children are born with a disorder that weakens the immune system) Which bacteria (or fungi) are likely to cause meningitis also depends on what is weakening the immune system and which part of the immune system is weakened, as in the following examples: , the bacteria that cause tuberculosis, or fungi (particularly Cryptococcosis ) Problems producing antibodies (which help the body fight infection) or removal of the spleen:Streptococcus pneumoniaeor, less often,Neisseria meningitidis, which may cause a rapid, severe form of meningitis Recent chemotherapy for cancer:Pseudomonas aeruginosaor gram-negative bacteria such asE. coli In very young infants (particularly premature infants) and older people, certain parts of the immune system may be weak, increasing the risk of meningitis due toListeria monocytogenes. 