Friday, October 24, 2008

Bacterial Meningitis

1.1. Bacterial Meningitis
1. Bacterial meningitis is a serious infection of the fluid in the spinal cord and the fluid that surrounds the brain.
2. Bacterial meningitis is most commonly caused by one of three types of bacteria: Haemophilus influenzae type b, Neisseria meningitidis, and Streptococcus pneumoniae bacteria.
3. The bacteria are spread by direct close contact with the discharges from the nose or throat of an infected person.
4. Bacterial meningitis can be treated with antibiotics.
5. Prevention depends on use of vaccines, rapid diagnosis, and prompt treatment of close personal contacts.

1.2. Pathophysiology
Bacteria space by a hematogenous reach the subarachnoid route and may directly reach the meninges in patients with a parameningeal focus of infection.
Once pathogens enter the subarachnoid space, an intense host inflammatory response is triggered by lipoteichoic acid and other bacterial cell wall products produced as a result of bacterial lysis. This response is mediated by the stimulation of macrophage-equivalent brain cells that produce cytokines and other inflammatory mediators. This resultant cytokine activation then initiates several processes that ultimately cause damage in the subarachnoid space, culminating in neuronal injury and apoptosis.

Interleukin 1 (IL-1), tumor necrosis factor-alpha , and enhanced nitric oxide production play critical roles in triggering inflammatory response and ensuing neurologic damage. Infection and inflammatory response later affect penetrating cortical vessels, resulting in swelling and proliferation of the endothelial cells of arterioles. A similar process can involve the veins, causing mural thrombi and obstruction of flow. The result is an increase in intracellular sodium and intracellular water.

The development of brain edema further compromises cerebral circulation, which can result in increased intracranial pressure and uncal herniation. Increased secretion of antidiuretic hormone resulting in the syndrome of inappropriate antidiuretic hormone secretion (SIADH) occurs in most patients with meningitis and causes further retention of free water. These factors contribute to the development of focal or generalized seizures.

Severe brain edema also results in a caudal shift of midline structures with their entrapment in the tentorial notch or foramen magnum. Caudal shifts produce herniation of the parahippocampal gyri, cerebellum, or both. These intracranial changes appear clinically as an alteration of consciousness and postural reflexes. Caudal displacement of the brainstem causes palsy of the third and sixth cranial nerves. If untreated, these changes result in decortication or decerebration and can progress rapidly to respiratory and cardiac arrest.
Aetiology /prevalence/inciden
1. VIRAL MENINGITIS is usually relatively mild. It clears up within a week or two without specific treatment. Viral meningitis is also called aseptic meningitis.
2. BACTERIAL MENINGITIS Acute bacterial meningitis is the most common form of meningitis. Approximately 80 percent of all cases are acute bacterial meningitis. Bacterial meningitis can be life threatening. The infection can cause the tissues around the brain to swell. This in turn interferes with blood flow and can result in paralysis or even stroke.
is much more serious. It can cause severe disease that can result in brain damage and even death.

Cause bacterial meningitis
Meningitis is caused by the following pathogens in each age group:
1. Neonates - Group B or D streptococci, nongroup B streptococci, Escherichia coli, and L monocytogenes
2. Infants and children - H influenzae (48%), S pneumoniae (13%), and N meningitidis
3. Adults - S pneumoniae, (30-50%), H influenzae (1-3%), N meningitidis (10-35%), gram-negative bacilli (1-10%), staphylococci (5-15%), streptococci (5%), and Listeria species (5%)
Risk factors
o Aged 60 years or older
o Aged 5 years or younger, especially children with diabetes mellitus, renal or adrenal insufficiency, hypoparathyroidism, or cystic fibrosis
o Immunosuppressed patients are at increased risk of opportunistic infections and acute bacterial meningitis. Immunosuppressed patients may not show dramatic signs of fever or *meningeal inflammation.
Crowding (eg, military recruits and college dorm residents) increases risk of outbreaks of meningococcal meningitis.
* Splenectomy and sickle cell disease increase the risk of meningitis secondary to encapsulated organisms.
* Alcoholism and cirrhosis: Multiple etiologies of fever and seizures in these patients make meningitis challenging to diagnose.
* Diabetes
*Recent exposure to others with meningitis, with or without prophylaxis
* Contiguous infection (eg, sinusitis)
* Dural defect (eg, traumatic, surgical, congenital)
* Thalassemia major
* Intravenous (IV) drug abuse
* Bacterial endocarditis
* Ventriculoperitoneal shunt
* Malignancy (increased risk of Listeria species infection)
* Some cranial congenital deformities
The bacteria often live harmlessly in a person's mouth and throat. In rare instances, however, they can break through the body's immune defenses and travel to the fluid surrounding the brain and spinal cord. There they begin to multiply quickly. Soon, the thin membrane that covers the brain and spinal cord (meninges) becomes swollen and inflamed, leading to the classic symptoms of meningitis.
The bacteria are spread by direct close contact with the discharges from the nose or throat of an infected person. Fortunately, none of the bacteria that cause meningitis are very contagious, and they are not spread by casual contact or by simply breathing the air where a person with meningitis has been.

Signs And Symptoms Of Bacterial Meningitis
Common symptoms are high fever, headache, and stiff neck. These symptoms can develop over several hours, or they may take 1 to 2 days. Other symptoms can include nausea, vomiting, sensitivity to light, confusion, and sleepiness. In advanced disease, bruises develop under the skin and spread quickly.
In newborns and infants, the typical symptoms of fever, headache, and neck stiffness may be hard to detect. Other signs in babies might be inactivity, irritability, vomiting, and poor feeding.
As the disease progresses, patients of any age can have seizures.

Risk for bacterial meningitis
Anyone can get bacterial meningitis, but it is most common in infants and children. People who have had close or prolonged contact with a patient with meningitis caused by Neisseria meningitidis or Hib can also be at increased risk. This includes people in the same household or day-care center, or anyone with direct contact with discharges from a meningitis patient's mouth or nose.
The diagnosis is usually made by growing bacteria from a sample of spinal fluid. The spinal fluid is obtained by a spinal tap. A doctor inserts a needle into the lower back and removes some fluid from the spinal canal. Identification of the type of bacteria responsible for the meningitis is important for the selection of correct antibiotic treatment.
Advanced bacterial meningitis can lead to brain damage, coma, and death. Survivors can suffer long-term complications, including hearing loss, mental retardation, paralysis, and seizures.

• In general, mortality rates vary with age and pathogen, with the highest being for S pneumoniae. Despite effective antimicrobial and supportive therapy, mortality rates among neonates remain high, with significant long-term sequelae in survivors. Bacterial meningitis also causes long-term sequelae and results in significant morbidity beyond the neonatal period. Mortality rates are highest during the first year of life, decreasing in mid life and increasing again in elderly persons.
• Despite advances in care for patients with bacterial meningitis, the overall case fatality remains steady at approximately 10-30%.

Bacterial meningitis is treated with antibiotics. A general intravenous antibiotic with a corticosteriod to bring down the inflammation may be prescribed even before all the test results are in. When the specific bacteria are identified, your doctor may decide to change antibiotics. In addition to antibiotics, it will be important to replenish fluids lost from loss of appetite, sweating, vomiting and diarrhea.

There is a 10% death rate from bacterial meningitis but if diagnosed and treated early enough, most people recover.
There may be permanent damage to brain stem. Seizures, mental impairment and paralysis may be life long.

1. Vaccines -- There are vaccines against Hib, some strains of Neisseria meningitidis, and many types of Streptococcus pneumoniae.
a. The vaccines against Hib are very safe and highly effective. By age 6 months of age, every infant should receive at least three doses of an Hib vaccine. A fourth dose (booster) should be given to children between 12 and 18 months of age.
b. The vaccine against Neisseria meningitidis (meningococcal vaccine) is not routinely used in civilians in the United States and is relatively ineffective in children under age 2 years. The vaccine is sometimes used to control outbreaks of some types of meningococcal meningitis in the United States. New meningococcal vaccines are under development.
c. The vaccine against Streptococcal pneumoniae (pneumococcal vaccine) is not effective in persons under age 2 years but is recommended for all persons over age 65 and younger persons with certain medical problems. New pneumococcal vaccines are under development.
2. Disease reporting -- Cases of bacterial meningitis should be reported to state or local health authorities so that they can follow and treat close contacts of patients and recognize outbreaks.
3. Treatment of close contacts -- People who are identified as close contacts of a person with meningitis caused by Neisseria meningitidis can be given antibiotics to prevent them from getting the disease. Antibiotics for contacts of a person with Hib disease are no longer recommended if all contacts 4 years of age or younger are fully vaccinated.
4. Travel precautions -- Although large epidemics of bacterial meningitis do not occur in the United States, some countries experience large, periodic epidemics of meningococcal disease. 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.
The CDC recommends the meningococcal vaccine for:
1. All children and adolescents ages 11 through 18
2. College freshmen living in dormitories
3. Military recruits
4. Scientists routinely exposed to meningococcal bacteria
5. Anyone traveling to or living in a part of the world where the disease is common, such as Africa
6. Anyone with a damaged spleen or who has had his or her spleen removed
7. Anyone who has terminal complement component deficiency (an immune system disorder)
The CDC does not recommend the vaccine for:
1. Anyone who has ever had a severe (life threatening) allergic reaction to a previous dose of meningococcal vaccine.
2. Anyone who has a severe (life threatening) allergy to any vaccine component. Tell your doctor if you have any severe allergies.
The CDC recommends that the following individuals wait before receiving the vaccine or talk further with their doctor about the need for the vaccine:
1. Anyone who is moderately or severely ill at the time of their scheduled appointment to receive their shot should wait until they recover.
2. Anyone who has ever had Guillain-Barre syndrome should discuss getting the vaccine with his or her doctor.
3. Pregnant women should only get the vaccine if it is clearly needed. Discuss the need with your doctor.
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