Acute Bacterial Meningitis
What is meningitis?
Meningitis is the infection and inflammation of the meninges (covering of the brain and spinal cord: duramater, arachnoid and piamater) and the cerebrospinal fluid. Meningitis is usually caused by bacteria. Virus and fungi can also cause meningitis. Knowing whether meningitis is caused by a virus or bacterium is important because the severity of illness and the treatment differ. Viral meningitis is generally less severe and resolves without specific treatment, while bacterial meningitis can be quite severe and may result in brain damage, hearing loss, or learning disability.
What causes meningitis?
The causative organism that involved in meningitis varies with the age of the patient. In newborn it is due to gram-negative bacilli (E.Coli and klebsiella pneumoniae) and group B Streptococcus whereas Haemophilus influenza type b (Hib) is the leading cause in children aged between 2 months to 4 years. In adults the causative organism are Neisseria meningitides and streptococcus pneumoniae. Tuberculosis is now rare cause of meningitis in U.S. but may increase due to epidemic of AIDS.
How does the organism reach the CSF?
The organism may reach the meninges and CSF (cerebrospinal fluid- fluid that surrounds the brain) through bloodstream; by retrograde propagation from the nasopharynx or direct spread from adjacent foci of infection (like osteomyelitis of skull or sinusitis). It may also be caused by a fracture of the base of skull with a tear in the duramater resulting CSF leak. The integrity of the meninges is a major factor in our resistance to acquisition of meningitis.
Symptoms and diagnosis of meningitis
Many cases of bacterial meningitis are preceded by symptoms of upper respiratory infection. But usually symptoms present for less than 72 hours before admission. High fever, severe generalized headache, photophobia (sensitivity to light), confusion and neck stiffness are common findings. Nausea, vomiting and anorexia (lack of interest in drinking and eating) may also be present. Back pain and muscle pains are frequently present and may be very severe. A meningitis patient may be alert at the onset but may rapidly deteriorate through delirium and obtundation to coma. In young children, there may be history of exposure to another person with systemic infection caused by meningococcus or Haemophilus. A patient with meningitis may look very ill. There is always high fever, often above 39 degree Celsius. Signs of meningeal inflammation, including neck stiffness and positive Kernig's and Brudzinki's sign are usual. In infants and neonates, the manifestations are different. Neck stiffness is often absent and the temperature may be low or normal. Irritability may be the only finding.
What are the lab investigations for meningitis?
Diagnosis is primarily based on examination of CSF. A sample of CSF is obtained through spinal tap. Isolation and identification of the organism is the definitive step in the management of the patient with meningitis. In acute bacterial meningitis, culturing of blood samples before starting of treatment yields organisms in 50-70 percent of the patients. Throat swab must be also sent for culture. Cell count in CSF will be more than 500cells/cu.mm and protein more than 100mg/dl while glucose is reduced (less than 40mg/dl).
What other disease may be confused with meningitis?
In a person suffering from acute bacterial meningitis several complications can arise. These complications include, cerebral edema (fluid retention in the brain leading to increased brain pressure), seizures, venous thrombosis (clot in the blood vessels or brain), brain abscess, subdural effusion and shock.
How do you treat meningitis?
Treatment is aimed at providing adequate support to the critically ill patient and to eradicate the infecting organism with antimicrobial therapy. The ideal antibiotic for treatment of bacterial meningitis should have three characteristics: good penetration into the CSF, bactericidal activity in the CSF, and proven efficacy in clinical practice. Penicillin remains the drug of choice for meningococcal meningitis. Third generation cephalosporins are currently the drug of choice for meningitis of unknown cause in otherwise healthy adults.
How to prevent meningitis?
There are vaccines against Hib and against some strains of N. meningitidis and many types of Streptococcus pneumoniae. The vaccines against Hib are very safe and highly effective.
There is also a vaccine that protects against four strains of N. meningitidis, but it is not routinely used in the United States. The vaccine against N. meningitidis is sometimes used to control outbreaks of some types of meningococcal meningitis in the United States. Meningitis cases should be reported to state or local health departments to assure follow-up of close contacts and recognize outbreaks. College freshman, especially those who live in dormitories are at higher risk for meningococcal disease and should be educated about the availability of a safe and effective vaccine, which can decrease their risk. Although large epidemics of meningococcal meningitis do not occur in the United States, some countries experience large, periodic epidemics. Overseas travelers should check to see if meningococcal vaccine is recommended for their destination. Travelers should receive the vaccine at least 1 week before departure, if possible. Information on areas for which meningococcal vaccine is recommended can be obtained by calling the Centers for Disease Control and Prevention at (404)-332-4565.