Bacteria that enter the bloodstream of the brain and spinal cord cause acute bacterial meningitis. But this can also happen if bacteria penetrate directly into the meninges. This can be caused by an ear infection or sinusitis, a skull fracture or, more rarely, following certain surgeries. Multiple bacterial strains can cause acute bacterial meningitis, mostly:
This bacterium is the leading cause of bacterial meningitis in infants, toddlers, and adults in the United States. It usually causes pneumonia or infections of the ear or sinuses. A vaccine can help prevent this infection.
This bacterium is another major cause of bacterial meningitis. These bacteria usually cause upper respiratory infection but can cause meningococcal meningitis when they enter the bloodstream. It is a highly contagious infection that affects mostly adolescents and young adults. Local epidemics can occur in student dormitories, boarding schools, and military bases. A vaccine can help to prevent infections.
Haemophilus influenzae (Haemophilus).
The bacterium Haemophilus influenzae type B (Hib) was once the leading cause of bacterial meningitis in children. However, new vaccines against Hib have drastically reduced the number of cases of this type of meningitis.
Listeria monocytogenes (Listeria).
These bacteria can be found in unpasteurized cheese, hot dogs and cold cuts. Meningitis most common in pregnant women, newborns, the elderly and people with weakened immune systems. Listeria can cross the placental barrier and end of pregnancy infections can be fatal to the baby.
Viral meningitis is usually benign and often disappears by itself. In the United States, most cases are caused by a group of viruses called enteroviruses. These viruses occur more frequently in late summer and early autumn. Viruses such as herpes simplex virus, HIV, mumps, West Nile virus and others can also cause viral meningitis.