Bacterial meningitis is an acute infection responsible for many deaths and neurological sequelae. The bacterium Neisseria meningitidis , also called meningococcus, has great epidemiological importance, because it presents a constant risk of epidemics and high rates of morbidity and mortality. However, with therapeutic advances and advanced support measures, they have reduced lethality, which now ranges from 5 to 20%. Therefore, early diagnosis and treatment is of fundamental importance.
THE CHALLENGES OF CLINICAL DIAGNOSIS
Meningitis means inflammation of the meninges, which are the protective layers that surround the brain and spinal cord. It can be caused by viruses, bacteria, fungi, or by non-infectious processes, such as lesions and tumors. However, the most frequent forms are viral and bacterial meningitis, which also concentrate the most serious cases and with the highest mortality rate. Therefore, both are considered an important public health issue, due to their ability to cause outbreaks.
The symptoms of the two forms are very similar: febrile syndrome with neurological signs, often mistaken for the flu. In the case of meningococcal disease, patients may develop febrile hemorrhagic syndrome , and be confused, for example, with a condition of dengue .
In viral cases, the symptoms develop more slowly and without so much severity, and there is no specific treatment, since the disease usually resolves on its own after a few weeks, as with other viruses. On the other hand, the bacterial progresses very fast and can be fatal if not treated quickly. Therefore, late treatment can result in sequelae such as brain damage, hearing and vision loss and even limb amputation.
In controlling bacterial disease, the most effective measure is not related to treatment, but prevention, the use of vaccines, specifically against Haemophilus influenzae B . The effectiveness is unquestionable. In addition, it is known that any bacteria can cause meningitis in a susceptible individual. But Haemophilus influenzae type B, Neisseria meningitidis and Streptococcus pneumoniae (pneumococcus) are the agents responsible for approximately 95% of the cases.
THE IMPORTANCE OF CAUSING AGENT DIFFERENTIATION
The treatment measures are different for each type of meningitis, so knowing whether the cause is bacterial is very important, since it determines the severity of the disease as well as the appropriate treatment.
The laboratory diagnosis of bacterial meningitis is carried out through the study of CSF cerebrospinal fluid (CSF), blood, as well as scraping of petechial lesions, characteristic of meningococcal disease.
The CSF aspect, although not considered an examination, works as an indication. Normal CSF is clear and colorless. However, in infectious processes, there is an increase in figured elements (cells), causing turbidity, the intensity of which varies according to the quantity and type of these elements.
The main tests for the diagnostic clarification of suspected cases of meningitis are:
- Chemocytological examination of CSF
- Direct bacterioscopy (liquor and other fluids)
- Culture (liquor, blood, petechiae)
- Cross-immunelectrophoresis – CIE (CSF and serum)
- Agglutination by latex (liquor and serum)
The most used methodologies for the differentiation of the etiologic agent are direct bacterioscopic exams (Gram method) and growth in culture medium, which is considered the gold standard. However, the difficulty lies in the sensitivity of both methods, which can vary from 60 to 85% in direct examination and from 70 to 85% in culture. In addition to the direct visualization of the bacteria, the presence of more common bacterial antigens can be investigated through latex testing. This method, combining both speed and great sensitivity, uses latex particles marked with specific bacterial antibodies, which on contact with a CSF sample containing bacterial antigen reacts with agglutination visible to the naked eye.
| CSF Analysis in Bacterial Meningitis | |
| Aspect | Cloudy |
| Color | Milky white or slightly xanthochromic |
| Clot | Presence or absence |
| Chlorides | Decreased |
| Glucose | Decreased |
| Total Proteins | Increased |
| Globulins | Positive (Gamma Globulin) |
| Leukocytes | 200 to thousands (neutrophils) |
| Counterimmunoelectrophoresis (CIE) | Reagent |
| Latex | Reagent |
| Microscopy | Positive for DGN, BGN, CGP, BGPb or not |
| Culture | Growth in chocolate agar |
Table: Guide to epidemiological surveillance / Ministry of Health, Health Surveillance Secretariat, Department of Epidemiological Surveillance. – 7. ed. – Brasília: Ministry of Health, 2009.
THE NEXT STEP: MOLECULAR DIAGNOSIS FOR MENINGITIS
Today we know that, with the advancement of medicine, new knowledge about pathophysiology, the emergence of new antibiotics and growing bacterial resistance have resulted in changes in the diagnosis and treatment of various diseases.
Thus, in this scenario, laboratory tests by molecular biology are important allies of medical treatment: through the PCR technique (Polymerase chain reaction), they identify through the genetic material the agents that cause meningitis and other infectious diseases, offering results faster and with high sensitivity and specificity. In addition, multiplex panels also allow the detection of several pathogens simultaneously in a single test, with a single sample
