IStock Photo 1324463 © Robert Musser

The initial symptoms of meningitis can easily be mistaken for the flu.

The term meningitis simply refers to an inflammation (“itis”) of the membrane (“meninges”) and fluid that surround the brain and spinal cord. Sometimes called spinal meningitis, the disease is usually caused by a bacterial or viral infection that leads to its hallmark symptoms of a stiff neck, headache, and high fever.

Meningitis outbreaks make headlines for two reasons. First, the disease can progress at breakneck speed. Some who catch it initially seem only mildly sick; hours later, they are hospitalized—often facing life-threatening complications like vein collapse, gangrene, and organ failure. Second, although anyone can catch meningitis, it strikes a disproportionately high number of young, otherwise healthy people, often during late high school or their freshman year of college.

The odds a person will die from meningitis—viral or bacterial—in a given year are 1 in 472,200. Those odds are based on statistics from the US in 2006; of all the deaths that occurred that year, 1 in 3,827 was due to meningitis. However, meningitis is relatively common in the deaths of children: it was to blame for 1 in 467.7 infant deaths, 1 in 231.6 deaths of children between 1 and 4 years old, and 1 in 409.9 deaths of kids 5–14 years old. As we age, we become more likely to die of something else.

Fortunately, viral meningitis, which is not susceptible to antibiotics, packs less of a punch than its bacterial counterpart. Enteroviruses cause about 90% of viral meningitis cases, most of which are mild. Patients usually make a full recovery in a week or two.

The usual suspects in the more severe bacterial meningitis are Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type b (Hib). Hib used to be the leading cause of bacterial meningitis in children under five years, but widespread vaccination of infants dramatically dropped the disease’s incidence. Vaccines against Neisseria and Streptococcus are also available; however, they are not universally required and do not protect against all variants of these bacteria. Streptococcus pneumonia is now the most common cause of meningitis in young children and infants.

Neisseria causes a form of meningitis known as meningococcal disease, which is often the cause of highly publicized meningitis outbreaks in college dorms.

Patients with bacterial forms of meningitis are treated with antibiotics, but things may get much worse before they get better. As the drugs kill the bacteria, dead bacterial cells break apart and release toxic compounds called endotoxins into the body. Reactions to these toxins cause some of the worst symptoms of meningococcal disease and are often fatal.

The odds a person will be diagnosed with invasive meningococcal disease in a year are 1 in 250,800. For males, the odds are 1 in 240,100; for females, 1 in 263,600. According to the Centers for Disease Control, 10–14% of those with meningococcal disease will die, while 11–19% of survivors will face serious complications that may be permanent, such as limb amputations, hearing loss or deafness, and brain damage.