Bacterial Meningitis Flashcards
what is the definition of bacterial meningitis?
Bacterial meningitis is a serious inflammation of the meninges caused by various bacteria. Streptococcus pneumoniae, Neisseria meningitidis and Haemophilus influenzae type b (Hib) are the predominant causative pathogens in adults.
what is the epidemiology of bacterial meningitis?
More common in africa
Vaccine against flu = reduction by 99% of this pathogen causing meningitis
what is the aetiology of bacterial meningitis?
The routine use of Haemophilus influenzae type b (Hib) and conjugate pneumococcal vaccines in the UK and other developed countries has markedly reduced the overall incidence of bacterial meningitis.
Streptococcus pneumoniae is the most common cause of bacterial meningitis in many countries worldwide. (PCV13 vaccine reducing incidence)
Neisseria meningitidis serogroup B is the predominant cause of meningococcal meningitis in Europe, the US, and the Western Pacific. Meningococcal serogroups C and W are most common in most of Africa and Latin America. Serogroup Y cases mostly occur in Nordic countries
Listeria monocytogenes is a common cause of bacterial meningitis in patients using immunosuppressive drugs, people who misuse alcohol, and patients with diabetes mellitus
what are the risk factors for bacterial meningitis?
Older age Crowding Exposure to pathogens Immunosuppressed Cranial anatomical defects/ ventriculoperitoneal shunt Cochlear implants Sickle cell
what is the pathophysiology for bacterial meningitis?
Bacteria reach the central nervous system either by haematogenous spread (the most common route) or by direct extension from a contiguous site. The bacteria multiply quickly once they have entered the subarachnoid space. Bacterial components in the cerebrospinal fluid induce the production of various inflammatory mediators, which in turn enhance the influx of leukocytes into the cerebrospinal fluid. The inflammatory cascade leads to cerebral oedema and increased intracranial pressure, which contribute to neurological damage and even death.
what are the key presentations of bacterial meningitis?
Headache Neck stiffness Fever Altered mental states Vomiting Confusion Photophobia Seizures Risk factors
what are the first line and gold standard investigations for bacterial meningitis?
Blood culture - positive
Serum pneumococcal and meningococcal PCR - positive for specific antigen
Blood glucose - hypo or hyper
FBC - leukocytosis anaemia and thrombocytopenia
Serum urea creatinine and electrolytes - acidosis, hypokalaemia, hypocalcaemia, hypomagnesaemia, low sodium may indicate tuberculous meningitis
Venous blood gas - shock may be indicated by a lactate concentration of >4 mmol/L
LFTs - raised
Coagulation screen - evidence of disseminated intravascular coagulation (prolonged thrombin time, elevated fibrin degradation products or D-dimer, low fibrinogen or antithrombin levels)
Serum HIV - if positive they may have a predisposition for meningitis
Serum procalcitonin - elevated or normal
Serum CRP - high
Cerebrospinal fluid protein - usually elevated >0.5
CSF lactate - >35 mg/dL suggests bacterial rather than viral meningitis
CSF glucose - CSF glucose concentration is <2.5 mmol/L (<45 mg/dL), or <40% of simultaneously measured serum glucose in bacterial meningitis
CSF microscopy - organisms seen on microscopy and cultures evident on culture medium
CSF cell count - polymorphonuclear pleocytosis with WBC count typically >1.0 x 109/L in untreated bacterial meningitis
CSF PCR for pneumococcus - may be positive
what are the differential diagnoses for bacterial meningitis?
Encephalitis Viral meningitis Drug-induced meningitis TB meningitis Fungal meningitis
how is bacterial meningitis managed?
Haemophilus influenzae:
Ceftriaxone or cefotaxime IV, moxifloxacin and corticosteroid
Enterobacteriaceae:
Ceftriaxone or cefotaxime or chloramphenicol IV
Streptococcus pneumoniae:
Ceftriaxone or cefotaxime or benzylpenicillin sodium or chloramphenicol IV and corticosteroid
Listeria monocytogenes:
Amoxicillin IV
Staphylococcus aureus:
non-MRSA = flucloxacillin and rifampicin IV
Penicillin allergic = vancomycin and rifampicin IV
MRSA = vancomycin or linezolid IV
how is bacterial meningitis monitored?
Repeat lumbar punctures to monitor treatment are not necessary if the patient is improving. Indications for repeated lumbar puncture include no clinical response after 48 hours of appropriate antimicrobial therapy and cerebrospinal fluid shunt infection, to ensure that the infection is responding to therapy
what are the complications of bacterial meningitis?
Shock
Elevated ICP
Hydrocephalus
what is the prognosis for bacterial meningitis?
The mortality rate of community-acquired bacterial meningitis is approximately 20% for all causes and up to 30% for pneumococcal meningitis. The mortality rate increases with age.
