Bacterial Meningitis is the most common form of suppurative CNS infection. It causes decreased consciousness, seizures, raised intracranial pressures and stroke and fever. The organism most often responsible are:
- Streptococcus pneumoniae (50%)
- Neisseria meningitides (25%)
- Group B streptococci (15%)
- Listeria monocytogenes (10%)
- Haemophilous influenza type b (Hib) less than 10%
- Ecoli, etc
All bacterial meningitis are not contagious. But those which are contagious, the infectivity of the disease depends on the virulence of the bacteria and host immune defense mechanism.
Meningococcus Infections – Who are at Risk?
Meningococcus infections are initiated by nasopharungeal colonization, which is due to spread of infection from one person to another by sharing respiratory or throat secretions (saliva or spit) or coughing, kissing and living in close contacts. Individuals with deficiency of any complement components, including properdin are highly susceptible to meningococcal infection.
Gram Negative Infections
Gram negative bacilli causes meningitis in individuals with chronic and debilitating diseases such as diabetes, cirrhosis , or alcoholism and in those with chronic urinary tract infections. Gram negative meningitis can also complicate neurosurgical procedures, particularly craniectomy and head trauma associated with CSF rhinorrhea or otorrhoea.
Ottitis, mastoidites, sinusitis are predisposing and associated conditions for meningitis due to streptococcal species, gram negative anaerobes, staphylococcus aureus, haemophilus sp. and enterobacteriacae.
Other Types of Meningitis Infections:
- Person suffering from endocarditis may develop meningitis due to HACEK Group (Haemophilus sp, Actinobacillus actinomycetemcomitans, cardiobacterium hominis, Eiknella corrodens, Kingella-kingae)
- Listeria monocytogenes is an important cause of meningitis in neonates (less than 1 month in age), pregnant women and individuals of less than 60 years and immune compromised of all ages. Infection is acquired by ingesting food contaminated by listeria.
- aureus and Coagulase negative Staphylococci are important causes of meningitis that occurs following invasive neurosurgical procedures, particularly shunting procedures for hydrocephalous or due to use of ommaya reservoirs.
- Group B streptococcus or streptococcus agalaetiae was previously responsible for meningitis in neonates but now it has been reported with increasing frequency in individuals less than 50 years of age particularly those with underlying diseases.
- influenza meningitis has been decreasing due to vaccinations.