Etiology
Different factors influence the cause and development of acute bacterial meningitis. They include the patient’s immune status, entry route, and patient’s age. In babies, the leading causes include B streptococci, Listeria monocytogenes, and Escherichia coli, among other gram-negative bacteria. In older kids and young people, Neisseria meningitis and Streptococci pneumoniae are the primary acute bacterial meningitis pathogens. N. meningitidis causes Waterhouse-Friderischsen syndrome and death within a short time. S. pneumoniae is the leading cause of the disease in adults and older people. In some cases, meningitis due to L. monocytogenes is common as the patient’s immune declines with age. Notably, Staphylococcus aureus causes acute meningitis in individuals of all ages.
Several routes of entry for acute bacterial meningitis exist. They include hematogenous spread, through head wounds, infected structures surrounding the head such as mastoid process, middle ear, and sinuses, infections after neurosurgical procedures, and acquired or congenital spine and skull defects. These conditions increase the probability of developing meningitis. In most cases, the causative bacteria depend on different immune deficiencies such as Hodgkin lymphoma, HIV/AIDS, and immunosuppression caused by drugs. Mycobacteria or L. monocytogenes depend on the above cell-mediated immunity defects. On the other hand, N. meningitidis and S. pneumoniae depend on splenectomy or humoral immunity defects to cause meningitis. Lastly, P. aeruginosa exploits neutropenia in its mechanism. Older adults with compromised immunity or infants are vulnerable to acute meningitis caused by L. meningitis. Thus, addressing these factors is essential when handling meningitis patients.
Symptoms and Signs
Meningitis symptoms are often visible three to five days after infection. During this phase, the patient develops non-specific signs and symptoms like vomiting, irritability, fever, and malaise. However, acute bacterial meningitis may be fulminant and rapid, making it a disorder that causes death in healthy-looking individuals very fast. Common signs and symptoms include headaches, fever, photophobia, nuchal rigidity, tachycardia, and obtundation, lethargy, and back pains. However, in neonates, nuchal stiffness, headaches, and fever may be absent. Infected neonates display paradoxical irritability. Seizures are frequent in children and adults with acute bacterial meningitis, while up to twelve percent of patients end up in coma or periodical unconsciousness. Chronic meningitis causes papilledema as intracranial pressure increases. However, papilledema can be attenuated or absent, depending on age and other related factors.
Bacteria causes several accompanying systemic infections. They include purpura, petechia, and rashes suggesting meningococcemia, pulmonary consolidation, and heart murmurs, implying endocarditis. Alcoholics or older patients with compromised immunity may not display nuchal rigidity and fever. Older adults often show confusion as the only symptom, especially those with dementia, and were previously alert. In such, similar to neonates and infants, there is a low threshold for performing a lumbar puncture. If a patient presents focal neurologic deficits or increased ICP, doctors can recommend CT scans or brain imaging (MRI). In some cases, symptoms may take long to appear or develop following the development of acute bacterial meningitis due to infections related to the neurosurgical procedure.
Diagnosis
Physicians can perform and lumbar puncture and blood cultures for cerebrospinal fluid analysis when they suspect acute bacterial meningitis. Lumbar puncture is necessary after blood analysis to compare glucose levels in the cerebrospinal fluid and blood. Appropriate treatment follows the following procedure. When a patient displays signs and symptoms suggesting bacterial meningitis, the doctor can administer corticosteroids and antibiotics before performing a lumbar puncture. Where the physician suspects bacterial meningitis and they delay lumbar puncture pending MRI and CT scans, they should prescribe corticosteroids and antibiotics after blood cultures. However, before performing neuroimaging, treatment should be delayed due to the need for confirmation.
Acute bacterial meningitis pathogens often pass through the hematogenous spread to reach the meninges and the subarachnoid space. They may also enter the meninges through an acquired or a congenital spine or skull defect. Since complement, immunoglobulins, white blood cells are usually absent or few in the cerebrospinal fluid, the causative pathogens do not cause inflammation as they multiply initially. Afterward, bacteria release teichoic acid and endotoxins and other chemicals, triggering inflammatory responses through mediators like tumor necrosis factor and white blood cells. As the cerebrospinal fluid (CSF) protein levels increase, the glucose levels drop since bacteria feed on glucose. Acute bacterial meningitis often affects brain parenchyma. Also, cortical ventriculitis and encephalitis accompany the subarachnoid space inflammation.
There are several complications related to acute bacterial meningitis. They include abducens palsy caused by inflammation of the sixth cranial nerve, hydrocephalus, subdural empyema, brain abscess due to infection of the cerebral parenchyma. Other complications are venous or arterial infarcts due to thrombosis and inflammation of veins and arteries in superficial or deep-lying brain regions. Different complications arise from acute bacterial meningitis treatment. Age is a significant consideration factor in this case, with infants and older adults with compromised immune systems at the highest risk. Also, wrong diagnosis or treatment for acute bacterial meningitis leads to severe complications that can be life threatening. These complications include loss of hearing, coma or unconsciousness, stroke, reduced cognition and brain damage, blindness, seizures, paralysis, and sepsis. Notably, adhering to treatment is essential in minimizing further healthcare complications.