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Meningitis, Encephalitis, and Sepsis

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Meningitis and Encephalitis

Meningitis is one of the most serious infections you can have. It is also one of the scariest -- understandably, since untreated some forms of meningitis can cause death or lasting impairment.

The meninges are membranes that enclose the brain and spinal cord. There are actually three layers of membrane: the "dura", which is a tough outer layer; the "arachnoid", which is a lacy, web-like middle layer; and the "pia", which is a delicate, fibrous inner layer containing many of the blood vessels that feed the brain and cord.

Meningitis, strictly speaking, is an inflammation of the meninges. (The suffix "-itis" stands for "inflammation".) Encephalitis is inflammation of the brain tissue itself: "encephal-" refers to the brain tissue. There are many causes for inflammation of tissue, and the meninges are no exception. However, the most common cause of meningeal inflammation is irritation caused by infection with bacteria or viruses. These organisms usually enter the meninges through the bloodstream from other parts of the body. Many meningitis-causing bacteria are carried in the nose and throat, often without the carrier having symptoms.

Viral meningeal infections are usually (but not always) less severe than bacterial infections. This is quite fortunate, since there are no antibiotic treatments available for most viruses and we must therefore let viral meningitis run its course by itself. Bacterial meningitis, on the other hand, must be treated with antibiotics in most cases to avoid severe consequences. Unfortunately the only way to confirm that meningitis is not bacterial is to culture the spinal fluid (actually the cerebrospinal fluid, since it bathes both the spinal cord and the brain) and see if there are bacteria in it. This can take 2-5 days. Since a bacterial meningitis can do a LOT of damage in 2-5 days, we always start antibiotics immediately after doing the spinal tap and keep giving the antibiotics until the culture has shown no bacteria for 2-5 days. This may seem wasteful (especially to bean-counters), but it is far better to treat all suspected meningitis patients promptly than to have to treat the long-term consequences of an untreated meningitis.

Since inflammation and resulting swelling seem to be the main cause of brain damage from meningitis, steroids have been used in some cases to help lessen the inflammation. Steroids usually are given along with antibiotics or just before the antibiotics are given, and may not be appropriate in all cases of meningitis.


"Sepsis" is the term we use for an overwhelming bacterial infection. Sepsis usually includes "bacteremia", or bacteria in the blood, although bacteremia can happen without sepsis (you will have bacteria in your blood briefly every time you brush your teeth...). Usually we reserve the term "sepsis" for patients whose infections are so severe that they are in shock; such infections happen more often when the immune system isn't working quite right (because of cancer, AIDS, malfunctioning organs or bone marrow, or other diseases). Very young babies do not have fully-functioning immune systems either and are thus susceptible to sepsis; this is why we routinely give IV antibiotics to any child under 2 months old who has a fever -- we cannot risk leaving sepsis untreated.

Among common bacterial causes of meningitis and sepsis are:

Neisseria menigitidis (Meningococcus)

Meningococcus is a bacteria often carried in the nose and throat without symptoms. It can be spread by droplets coughed or sneezed out by an infected person or by a carrier; many outbreaks of meningococcal infection occur in people living in close quarters (like schools, colleges, and military installations). It takes 1-10 days (most often 4 days or less) after exposure to show symptoms; patients are usually contagious until they have been treated for at least 24 hours.

Infection with meningococcus can cause meningitis, sepsis, or both. Oddly, someone with meningococcal infection with meningitis may do better than s/he would with sepsis and no meningitis; this does not always happen, though. Signs of meningococcal infection may include fever with chills and a rash; the classic rash of meningococcal infection is "petechial", caused by tiny blood clots just below the skin surface. In severe cases the infection can result in shock and death within a few hours even if treated. Also, as antibiotics kill the meningococci, the breakdown products of the dead bacteria can cause inflammation and abnormal blood clotting. Blood clotting in the wrong places can block blood flow to large parts of the body, and many patients with meningococcal sepsis lose fingers or toes, and sometimes hands, feet, or larger parts of their arms or legs, because of these clots.

In the past meningococcal infection was treated successfully with penicillin G. Unfortunately, some strains of meningococcus are resistant to penicillin G and must be treated with other antibiotics such as the third-generation cephalosporins.

There are many different groups or "serotypes" of meningococci, at least 8 of which can infect people. The most common infectious groups are labelled A, B, C, X, Y, Z, 29-E, and W-135 (and no, I don't know exactly how the labels were assigned...). Groups B and C are the groups most often seen in the United States. Unfortunately we do not yet have a good vaccine for group B. We do, however, have vaccines that protect against groups A, C, Y, and W-135.

The Advisory Committee on Immunization Practices and the Centers for Disease Control and Prevention now recommend that all children be vaccinated with the new meningococcus vaccine at age 11 or 12, and (as they have in the past) that all students entering college be vaccinated against groups A, C, Y, and W-135. The American Academy of Pediatrics also recommends that all entering college students get the vaccine, and many colleges and universities require their new students to be vaccinated. Travelers to countries where meningococcus is more common should also receive the vaccine, as should patients whose spleens have been removed or no longer work properly (such as patients with sickle-cell anemia, whose spleens eventually fail). Certain groups of people, such as military personnel, routinely receive the vaccine. Please see my meningococcus page for more information on meningococcus and the vaccines.

Streptococcus pneumoniae (Pneumococcus)

Pneumococci are even more common than meningococcus; in fact pneumococci are the most common cause of ear infections and sinus infections, as well as the most common bacteria found in the blood of children under 2 years old with fevers, many of whom have no obvious site of infection. Again, like meningococcus, many people have pneumococci in their noses and throats but have no symptoms. The bacteria is transmitted from one person to another, usually by droplets. Like viral upper respiratory infections, pneumococcal infections are more common in winter. Infection can begin as little as 1-3 days after exposure.

The signs of pneumococcal meningitis and sepsis can be the same as those of meningococcal meningitis. Often, however, pneumococcal infection can appear first as a high fever with a very high white-blood-cell count (where almost all of the white cells are neutrophils or bacteria-fighting cells) and no obvious site of infection.

Again, like meningococcus, pneumococcal infections could be treated with penicillin G, but penicillin-G-resistant pneumococci have become more and more common, especially with antibiotic overuse (this is one reason why we use so many different antibiotics to treat ear infections). We usually start meningitis or sepsis treatment with third-generation cephalosporins such as ceftriaxone until the cultures have been completed and we know what antibiotics can be used.

There are over 80 different know serotypes of pneumococcus. Some are more prevalent in different areas; some are more prevalent in children, while others are more common in adults. There is a vaccine available that protects against 23 of the known serotypes; as with meningococcus, the vaccine is given mainly to those at risk of severe infection, including those whose spleens no longer work properly. This vaccine does not provide complete or lifetime protection, does not work well in infants, and does not necessarily help prevent ear infections. However, there is a vaccine available that is intended for infants and children and that, although it only protects against 13 different serotypes, provides much better immunity. See my pneumococcus page for more information.

Haemophilus influenzae B (HiB)

Haemophilus influenzae B, or HiB, used to be the most common cause of bacterial meningitis in children, as well as a common cause of ear infections. That was before the introduction of vaccines against HiB in the late 1980's. Now we almost never see HiB meningitis -- another good reason to vaccinate. See my HiB page for more information on HiB and the vaccine.

As always, you should talk to your doctor about the vaccines, or about prophylactic antibiotics, and about their pros and cons before deciding whether to get them for your children or yourself.

Meningitis can be caused by other bacteria as well, including staphylococcus (found on everyone's skin) and Escherichia coli (E. coli -- the major bacteria in stool). Encephalitis can also be caused by several bacteria, including Bartonella henselae (the bacteria that causes cat-scratch disease).

Viral Meningitis and Viral Encephalitis

Although it is quite possible to have an overwhelming viral infection, generalized viral infections are common enough -- and usually not dangerous enough -- that we don't often consider viral sepsis as a separate problem. (Besides, we have no antibiotics to treat most viral infections, anyway.)

However, viral meningitis is a separate problem, and a common one at that. We can't treat viral meningitis either, but viral meningitis is usually less severe and causes less damage than bacterial meningitis. (I had viral meningitis myself as a teenager. I'm not quite normal, but it doesn't seem to have done too much damage...) Viral encephalitis, on the other hand, can do a great deal of damage since it attacks the brain tissue itself, and is just as untreatable as viral meningitis unless it is caused by one of the few viruses for which we have antibiotics (such as herpes simplex).

Many commmon viruses can cause meningitis. Among these are enteroviruses (like the polio viruses), varicella (the chickenpox virus), the mumps virus, adenoviruses, and many others. Notice that many of these viruses are ones we have vaccines for; a child who has been properly immunized against these viruses will likely not develop meningitis from them. However, if there is no vaccine for the virus there is no really good way to prevent meningitis caused by that virus except to stay away from people who have the virus -- which can be very hard, because a particular virus may infect hundreds of people but cause meningitis in only 1 or 2 of them.

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PLEASE NOTE: As with all of this Web site, I try to give general answers to common questions my patients and their parents ask me in my (real) office. If you have specific questions about your child you must ask your child's regular doctor. No doctor can give completely accurate advice about a particular child without knowing and examining that child. I will be happy to try and answer general questions about children's health, but unless your child is a regular patient of mine I cannot give you specific advice.

Copyright © 1998, 1999, 2000, 2001, 2003, 2004, 2005, 2006, 2007, 2011 Vinay N. Reddy, M.D. All rights reserved.
Written 02/14/98; major revision 10/11/00; major revision 04/24/05; major revision 09/14/05; last revised 07/05/11 counter