Microbiology
Infections
Question 77 of 77
A 72 year old patient presents to ED with a fever, headache and neck stiffness. You suspect meningitis. A lumbar puncture is performed and the results shown below. What is the most likely causative infective pathogen:
- WCC: 840 cells x 106/L (neutrophil predominance)
- Protein: markedly elevated
- Glucose: 2.1 mmol/L (blood glucose 6 mmol/L)
- Gram stain shows a Gram-positive diplococci
Answer:
The CSF analysis is characteristic of a bacterial meningitis. The most common causes of bacterial meningitis in this age group are Streptococcus pneumoniae (Gram-positive diplococci), Neisseria meningitidis (Gram-negative diplococci) and Listeria monocytogenes (Gram-positive rod).Meningitis
Microbiology / Infections
Last Updated: 16th June 2022
Infective Agents
- Viral causes
- Enteroviruses (Coxsackievirus, poliovirus and Enterovirus)
- Varicella zoster virus
- Herpes simplex virus
- Mumps virus
- Bacterial causes vary by age:
| Age | Pathogens |
|---|---|
| Neonate (< 1 month) | Group B Streptococcus, Escherichia coli, Listeria monocytogenes |
| Children (< 15 years) | Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae |
| Adult (< 55 years) | Streptococcus pneumoniae, Neisseria meningitidis |
| Adult (> 55 years) | Streptococcus pneumoniae, Neisseria meningitidis, Listeria monocytogenes |
| Immunosuppressed | Mycobacterium tuberculosis, Cryptococcus |
Clinical Disease
- Headache
- Photophobia
- Fever
- Neck stiffness
- Poor feeding/irritability
- Altered consciousness or confusion
- Kernig's sign (extension of flexed knee causes pain and resistance to movement)
- Brudzinski's sign (passive neck flexion causes bilateral hip and knee flexion)
- Bulging fontanelle
Diagnosis
- Lumbar puncture for CSF analysis, Gram-stain, microscopy and culture
- Blood for culture, rapid antigen detection and glucose determination
- CT head to exclude encephalitis
CSF Interpretation
- Physical characteristics
- Opening pressure: normally 10 - 20 cm H2O, may be elevated in infection or bleed
- Colour: clear and colourless is normal
- Turbidity: cloudy or turbid CSF may indicate the presence of WBCs, RBCs, microorganisms or an increase in protein levels
- Viscosity: ‘thick’ CSF may be seen in infection
- Biochemistry
- CSF glucose: usually about 2/3s that of serum glucose, may be decreased in bacterial or TB infection but usually remains normal in viral infection
- CSF protein: increase in protein may be seen in infection
- CSF lactic acid: usually raised in bacterial infection, but normal in viral infection
- CSF lactate dehydrogenase (LDH): usually raised in bacterial infection, but low or normal in viral infection
- CSF xanthochromia (bilirubin): seen following subarachnoid haemorrhage
- Microscopy
- CSF RBC count: presence of red blood cells may indicate bleeding into the CSF or a ‘traumatic tap’
- CSF WBC count: raised in infection or inflammation of the CNS
- CSF WBC differential: neutrophils increased in bacterial infection, an increase in lymphocytes with viral or TB infection
- Microbiology
- CSF Gram stain
- CSF culture and sensitivity
- CSF viral PCR testing
- Other specific tests depending on which organisms are suspected
| CSF Analysis | Normal (adults) | Bacterial | Viral | TB |
|---|---|---|---|---|
| Appearance | Clear and colourless | Turbid | Normal | Fibrin web |
| WCC (mm3) | 0 - 5 | High | High | High |
| Predominant cell type | - | Neutrophils | Lymphocytes | Lymphocytes |
| Glucose (mmol/L)
CSF:Serum Ratio |
2.5 - 4.4 mmol/L
0.6 |
Low | Normal | Low |
| Protein (g/L) | 0.2 - 0.4 | High | Normal or High | High |
Treatment
| Infection | Treatment |
|---|---|
| Initial empirical treatment for suspected meningitis |
|
| Meningitis caused by Meningococci spp. |
|
| Meningitis caused by Pneumococci spp. |
|
| Meningitis caused by Haemophilus influenzae |
|
| Meningitis caused by Listeria |
|
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
