Microbiology
Infections
Question 55 of 180
A one week old infant is brought to ED unwell. She is pyrexic, floppy and unresponsive with a bulging fontanelle. Empirical antibiotics are started and a lumbar puncture is performed which demonstrates Gram-negative rods. What is the most likely causative pathogen:
Answer:
Group B streptococcus (Gram positive cocci) and Escherichia coli (Gram negative rods) are the most common causes of neonatal meningitis. Another less common cause of neonatal meningitis is Listeria monocytogenes (Gram positive rods).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 |
