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Infectious Disease and Microbiology - Acute Meningitis
Acute meningitis is a rapidly developing inflammation of the meninges that typically evolves over hours to days. It may resolve spontaneously in viral cases or require urgent treatment when bacterial in origin. Despite advances in therapy, it remains a medical emergency due to its potential for rapid deterioration and severe complications.
Meningitis occurs worldwide and can affect individuals of all ages, including previously healthy people. The overall incidence in the United States is approximately 2–10 cases per 100,000 population annually, with significantly higher rates in neonates and young children. Among bacterial causes, Neisseria meningitidis is unique in its ability to cause epidemics. Vaccination programs have significantly reduced cases of Haemophilus influenzae type B meningitis.
Risk factors include extremes of age, crowded living conditions, close contact with infected individuals, head trauma, neurosurgical devices (e.g., shunts), immunosuppression, and chronic illnesses. Specific conditions predispose to certain pathogens—for example, asplenia increases risk for pneumococcal and meningococcal infections, while complement deficiencies increase susceptibility to meningococcal disease. Tick exposure may lead to Lyme meningitis.
The pathogenesis begins with colonization of the nasopharynx, followed by invasion into the bloodstream and crossing of the blood–brain barrier into the cerebrospinal fluid (CSF), where pathogens multiply. Inflammation in the subarachnoid space leads to increased intracranial pressure and neurologic dysfunction.
Etiologically, most cases are viral, particularly due to enteroviruses. However, bacterial meningitis is more severe and commonly caused by Streptococcus pneumoniae, Neisseria meningitidis, Group B Streptococcus, Listeria monocytogenes, and Haemophilus influenzae. Other pathogens include viruses (e.g., herpesviruses, HIV), spirochetes such as Treponema pallidum, and Borrelia burgdorferi.
Clinically, patients often present with fever, headache, vomiting, and altered mental status. Classical meningeal signs include nuchal rigidity, Kernig’s sign, and Brudzinski’s sign, although these may not always be present. A petechial or purpuric rash suggests meningococcal infection. Severe cases may progress to seizures, coma, or focal neurologic deficits.
Presentation may be atypical in elderly patients and neonates.
Diagnosis requires urgent evaluation. Initial laboratory tests include blood work and cultures, followed by lumbar puncture to analyze CSF. In bacterial meningitis, CSF typically shows high white blood cell count with neutrophil predominance, low glucose, and elevated protein. In viral meningitis, lymphocytes predominate, and glucose is usually normal. PCR testing improves detection of both bacterial and viral pathogens. A CT scan of the head is indicated before lumbar puncture in patients with risk factors for increased intracranial pressure or focal neurologic signs.
Treatment must be initiated immediately, often before confirmation of the causative organism. Empiric therapy typically includes a third- or fourth-generation cephalosporin combined with vancomycin, with the addition of ampicillin when Listeria is suspected. Therapy is later tailored based on culture results. Adjunctive corticosteroids may be beneficial in certain cases, particularly pneumococcal meningitis, to reduce inflammation and neurologic complications.
All patients require hospitalization for close monitoring and supportive care. Prognosis depends on factors such as age, underlying health, pathogen, and timeliness of treatment. Mortality and morbidity increase with delayed therapy, altered consciousness, or severe disease at presentation.
Complications can be severe and include seizures, hydrocephalus, brain abscess, hearing loss, cognitive impairment, paralysis, and even death. Survivors often require long-term neurologic follow-up and rehabilitation.
Acute meningitis is a rapidly developing inflammation of the meninges that typically evolves over hours to days. It may resolve spontaneously in viral cases or require urgent treatment when bacterial in origin. Despite advances in therapy, it remains a medical emergency due to its potential for rapid deterioration and severe complications.
Meningitis occurs worldwide and can affect individuals of all ages, including previously healthy people. The overall incidence in the United States is approximately 2–10 cases per 100,000 population annually, with significantly higher rates in neonates and young children. Among bacterial causes, Neisseria meningitidis is unique in its ability to cause epidemics. Vaccination programs have significantly reduced cases of Haemophilus influenzae type B meningitis.
Risk factors include extremes of age, crowded living conditions, close contact with infected individuals, head trauma, neurosurgical devices (e.g., shunts), immunosuppression, and chronic illnesses. Specific conditions predispose to certain pathogens—for example, asplenia increases risk for pneumococcal and meningococcal infections, while complement deficiencies increase susceptibility to meningococcal disease. Tick exposure may lead to Lyme meningitis.
The pathogenesis begins with colonization of the nasopharynx, followed by invasion into the bloodstream and crossing of the blood–brain barrier into the cerebrospinal fluid (CSF), where pathogens multiply. Inflammation in the subarachnoid space leads to increased intracranial pressure and neurologic dysfunction.
Etiologically, most cases are viral, particularly due to enteroviruses. However, bacterial meningitis is more severe and commonly caused by Streptococcus pneumoniae, Neisseria meningitidis, Group B Streptococcus, Listeria monocytogenes, and Haemophilus influenzae. Other pathogens include viruses (e.g., herpesviruses, HIV), spirochetes such as Treponema pallidum, and Borrelia burgdorferi.
Clinically, patients often present with fever, headache, vomiting, and altered mental status. Classical meningeal signs include nuchal rigidity, Kernig’s sign, and Brudzinski’s sign, although these may not always be present. A petechial or purpuric rash suggests meningococcal infection. Severe cases may progress to seizures, coma, or focal neurologic deficits.
Presentation may be atypical in elderly patients and neonates.
Diagnosis requires urgent evaluation. Initial laboratory tests include blood work and cultures, followed by lumbar puncture to analyze CSF. In bacterial meningitis, CSF typically shows high white blood cell count with neutrophil predominance, low glucose, and elevated protein. In viral meningitis, lymphocytes predominate, and glucose is usually normal. PCR testing improves detection of both bacterial and viral pathogens. A CT scan of the head is indicated before lumbar puncture in patients with risk factors for increased intracranial pressure or focal neurologic signs.
Treatment must be initiated immediately, often before confirmation of the causative organism. Empiric therapy typically includes a third- or fourth-generation cephalosporin combined with vancomycin, with the addition of ampicillin when Listeria is suspected. Therapy is later tailored based on culture results. Adjunctive corticosteroids may be beneficial in certain cases, particularly pneumococcal meningitis, to reduce inflammation and neurologic complications.
All patients require hospitalization for close monitoring and supportive care. Prognosis depends on factors such as age, underlying health, pathogen, and timeliness of treatment. Mortality and morbidity increase with delayed therapy, altered consciousness, or severe disease at presentation.
Complications can be severe and include seizures, hydrocephalus, brain abscess, hearing loss, cognitive impairment, paralysis, and even death. Survivors often require long-term neurologic follow-up and rehabilitation.
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