Laboratory Diagnosis of Meningitis
Meningitis is an infection of the membranes (meninges) surrounding the brain and spinal cord. Meningitis is usually of multiple etiology-bacterial, fungal or viral yet bacteria remain the common etiological agent (Reid & Fallon, 1992). Meningitis can be acute, with a quick onset of symptoms, or chronic, lasting a month or more, or can be mild or aseptic, but the emphasis should be on identification of cause so that appropriate interventions can be applied. Bacterial meningitis continues to be a potentially life threatening emergency with significant morbidity and mortality throughout the world and is an even more significant problem in many other areas of the world, especially in developing countries (Carbonnelle, 2009, Brouwer et al., 2010). Types of bacteria that cause bacterial meningitis vary by age group. Currently, the average age of contracting meningitis is above 25 years with Streptococcus pneumoniae, Neisseria meningitidis and Haemophilus influenzae being the most common pathogens (Ogunlesi et al., 2005, Brain, 2004 as cited in Maleeha Aslam et al., 2006). Trauma to the skull gives bacteria the potential to enter the meningeal space. Similarly, individuals with a cerebral shunt or related device are at increased risk of infection through those devices. In these cases, infections with Staphylococci, Pseudomonas aeruginosa and other gram-negative bacilli are more likely. Recurrent bacterial meningitis may be caused by persisting anatomical defects, either congenital or acquired, or by disorders of the immune system. (Brouwer et al., 2010) Tuberculous meningitis (TBM), is common in those from countries where tuberculosis is common, and is also encountered in those with immune problems, such as AIDS. Despite advancement in vaccine development and chemoprophylaxis bacterial meningitis remains a major cause of death and neurological disabilities which can be prevented by rapid and accurate diagnosis with prompt treatment which is essential for good outcome (Carbonnelle, 2009). Viral meningitis is generally less severe and clears up without specific treatment. Viral ("aseptic") meningitis is serious but rarely fatal in people with normal immune systems. Usually, the symptoms last from 7 to 10 days and the patient recovers completely. Often, in early phases of viral meningitis and bacterial meningitis, the symptoms are almost similar (Carbonnelle, 2009). Fungal meningitis is rare, but can be life threatening. Although anyone can get fungal meningitis, people at higher risk are those who have AIDS, leukemia, or other forms of immunodeficiency. The most common cause of fungal meningitis in HIV, is Cryptococcus spp. In the last two decades, more elaborative use of intensive care units for serious medical disorders, advancements in transplant procedures and concomitant use of immunosuppressive therapies as well as the pandemic spread of HIV, etc. have increased the incidence of Central Nervous System (CNS) fungal infections which present with various clinical syndromes: meningitis commonly. The clinical picture may mimic TBM and therefore, needs careful evaluation. The CNS mycoses carry higher risks of morbidity and mortality as compared to other infective processes and therefore promptly require precise diagnosis and appropriate medical and/or surgical management strategies to optimize the outcome (Raman Sharma, 2010). Chemical meningitis can develop after neurosurgical procedures and can be differentiated from bacterial meningitis by Cerebrospinal fluid (CSF) glucose levels and CSF White Blood Cell (WBC) values. The causes of non–infectious meningitis include cancers, systemic lupus erythematosus, drug induced, head trauma, brain surgery etc.