Acute Bacterial Meningitis

In neonates Neonatal Bacterial Meningitis Neonatal bacterial meningitis is inflammation of the meninges due to bacterial invasion. Signs are those of sepsis, central nervous system irritation (eg, lethargy, seizures, vomiting, irritability... read more and young infants, the most common causes of bacterial meningitis are

In older infants, children, and young adults, the most common causes of bacterial meningitis are

N. meningitidis meningitis occasionally causes death within hours. Sepsis caused by N. meningitidis sometimes results in coagulopathy and bilateral adrenal hemorrhagic infarction (Waterhouse-Friderichsen syndrome).

Haemophilus influenzae type B, previously the most common cause of meningitis in children < 6 years and overall, is now a rare cause in the US and Western Europe, where the H. influenzae vaccine is widely used. However, in areas where the vaccine is not widely used, H. influenzae is still a common cause, particularly in children aged 2 months to 6 years.

In middle-aged and in older adults, the most common cause of bacterial meningitis is

Less commonly, N. meningitidis causes meningitis in middle-aged and older adults. As host defenses decline with age, patients may develop meningitis due to L. monocytogenes or gram-negative bacteria.

In people of all ages, Staphylococcus aureus occasionally causes meningitis.

Routes of entry include the following:

Having any of the above conditions increases the risk of acquiring meningitis.

Overall, the most common causes of bacterial meningitis in immunocompromised patients are

But the most likely bacteria depend on the type of immune deficiency:

In very young infants (particularly preterm infants) and older adults, T-cell immunity may be weak; thus, these age groups are at risk of meningitis due to L. monocytogenes.

Unless contraindicated, lumbar puncture Lumbar Puncture (Spinal Tap) Lumbar puncture is used to do the following: Evaluate intracranial pressure and cerebrospinal fluid (CSF) composition (see table Cerebrospinal Fluid Abnormalities in Various Disorders) Therapeutically... read more (see also How To Do Lumbar Puncture How To Do Lumbar Puncture In lumbar puncture (LP), a needle is inserted into the lumbar subarachnoid space to collect cerebrospinal fluid (CSF) for laboratory testing, to measure CSF pressure, and sometimes to give intrathecal... read more ) is done immediately to obtain CSF for analysis, the mainstay of diagnosis.

Contraindications to immediate lumbar puncture are signs suggesting markedly increased intracranial pressure (ICP) or an intracranial mass effect (eg, due to edema, hemorrhage, or tumor). Thus, lumbar puncture should be considered high risk with any of the following:

In such cases, lumbar puncture may cause brain herniation Brain Herniation Brain herniation occurs when increased intracranial pressure causes the abnormal protrusion of brain tissue through openings in rigid intracranial barriers (eg, tentorial notch). Because the... read more and thus is deferred until neuroimaging (typically CT or MRI) is done to check for increased ICP or a mass effect. When lumbar puncture is deferred, treatment is best begun immediately (after blood sampling for culture and before neuroimaging). After ICP, if increased, has been lowered or if no mass effect or obstructive hydrocephalus is detected, lumbar puncture can be done.

CSF should be sent for analysis: cell count, protein, glucose, Gram staining, culture, PCR, and other tests as indicated clinically. A multiplex film-array PCR panel can provide rapid screening for multiple bacteria and viruses plus Cryptococcus neoformans in a CSF sample. This test, which is not always available, is used to supplement, not replace, culture and traditional tests. Simultaneously, a blood sample should be drawn and sent to have the CSF:blood glucose ratio determined. CSF cell count should be determined as soon as possible because white blood cells (WBCs) may adhere to the walls of the collecting tube, resulting in a falsely low cell count; in extremely purulent CSF, WBCs may lyse.

Typical CSF findings in bacterial meningitis include the following (see table ):

A CSF:blood glucose level of < 50% suggests possible meningitis. A CSF glucose level of ≤ 18 mg/dL or a CSF:blood glucose ratio of < 0.23 strongly suggests bacterial meningitis. However, changes in CSF glucose may lag 30 to 120 minutes behind changes in blood glucose. In acute bacterial meningitis, an elevated protein level (usually 100 to 500 mg/dL) indicates blood-brain barrier injury.

CSF cell count and protein and glucose levels in patients with acute bacterial meningitis are not always typical. Atypical CSF findings may include

When initial CSF findings are equivocal, a repeat lumbar puncture 12 to 24 hours later can sometimes clarify which direction CSF changes are heading or whether there was a laboratory error.

Identification of the causative bacteria in CSF involves Gram staining, culture, and, when available, PCR. Gram staining provides information rapidly, but the information is limited. For bacteria to be reliably detected with Gram stain, about 10⁵ bacteria/mL must be present. Results may be falsely negative if any of the following occur:

If clinicians suspect an anaerobic infection or other unusual bacteria, they should tell the laboratory before samples are plated for cultures. Prior antibiotic therapy can reduce the yield from Gram staining and culture. PCR, if available, and latex agglutination tests to detect bacterial antigens may be a useful adjunctive tests, especially in patients who have already received antibiotics.

Determination of antibiotic sensitivity requires bacterial culture.

Until the cause of meningitis is confirmed, other tests using samples of CSF or blood may be done to check for other causes of meningitis, such as viruses (particularly herpes simplex), fungi, and cancer cells.

Samples from other sites suspected of being infected (eg, urinary or respiratory tract) should also be cultured.

Antibiotics must be bactericidal for the causative bacteria and must be able to penetrate the blood-brain barrier.

If patients appear ill and findings suggest meningitis, antibiotics (see table ) and corticosteroids are started as soon as blood cultures are drawn and even before lumbar puncture. Also, if lumbar puncture is delayed pending neuroimaging results, antibiotic and corticosteroid treatment begins before neuroimaging.

Appropriate empiric antibiotics depend on the patient's age and immune status and route of infection (see table ). In general, clinicians should use antibiotics that are effective against S. pneumoniae, N. meningitidis, and S. aureus. In pregnant women, neonates, older patients, and immunocompromised patients, Listeria meningitis is possible; it requires specific antibiotic treatment, usually ampicillin. Herpes simplex encephalitis can clinically mimic early bacterial meningitis; thus, acyclovir is added. Antibiotic therapy may need to be modified based on results of culture and sensitivity testing.

Commonly used antibiotics include

Dexamethasone is used to decrease cerebral and cranial nerve inflammation and edema; it should be given when therapy is started. Adults are given 10 mg IV; children are given 0.15 mg/kg IV. Dexamethasone is given immediately before or with the initial dose of antibiotics and every 6 hours for 4 days.

Use of dexamethasone is best-established for patients with pneumococcal meningitis.

The effectiveness of other measures is less well-proved.

Patients presenting with papilledema or signs of impending brain herniation are treated for increased ICP with the following:

Hyperventilation is used until other measures become effective and is not used for more than 24 hours. When stopped, the PCO2 should be gradually increased to normal because a sudden increase may cause a significant increase in ICP.

Usually, adults are given mannitol 1 g/kg IV bolus over 30 minutes, repeated as needed every 3 to 4 hours or 0.25 g/kg every 2 to 3 hours, and children are given 0.5 to 2.0 g/kg over 30 minutes, repeated as needed.

Additional measures can include

Keeping patients in respiratory isolation (using droplet precautions) for the first 24 hours of therapy can help prevent meningitis from spreading. Gloves, masks, and gowns are used.

Vaccination can prevent certain types of bacterial meningitis.

A conjugated pneumococcal vaccine Pneumococcal Vaccine Pneumococcal disease (eg, otitis media, pneumonia, sepsis, meningitis) is caused by some of the > 90 serotypes of Streptococcus pneumoniae (pneumococci). Vaccines are directed against... read more effective against 13 serotypes, including > 80% of organisms that cause meningitis, is recommended for all children (see table ).

Routine vaccination against H. influenzae type b Haemophilus influenzae Type b (Hib) Vaccine Haemophilus influenzae type b (Hib) vaccines help prevent Haemophilus infections but not infections caused by other strains of H. influenzae bacteria. H. influenzae causes... read more is highly effective and begins at age 2 months.

A quadrivalent meningococcal vaccine Meningococcal Vaccine The meningococcal serogroups that most often cause meningococcal disease in the US are serogroups B, C, and Y. Serogroups A and W cause disease outside the US. Current vaccines are directed... read more is given to

During a meningitis epidemic, the population at risk (eg, college students, a small town) must be identified, and its size must be determined before proceeding to mass vaccination. The effort is expensive and requires public education and support, but it saves lives and reduces morbidity.

The meningococcal vaccine does not protect against serotype B meningococcal meningitis; this information should kept in mind when a vaccinated patient presents with symptoms of meningitis.

Anyone who has prolonged face-to-face contact with a patient who has meningitis (eg, household or day care contacts, medical personnel and other people who are exposed to the patient's oral secretions) should be given postexposure chemoprophylaxis.

For meningococcal meningitis, chemoprophylaxis consists of one of the following:

For meningitis due to H. influenzae type b, chemoprophylaxis is rifampin 20 mg/kg orally once a day (maximum: 600 mg/day) for 4 days. There is no consensus on whether children < 2 years require prophylaxis for exposure at day care.

Chemoprophylaxis is not usually needed for contacts of patients with other types of bacterial meningitis.