Bacterial Infection and Sepsis

• Meningitis and sepsis are medical conditions.
• Stephen Ritchie can be contacted via [email protected]

Brain Anatomy

• The brain is protected by the skull and several layers of membranes called meninges.
• The meninges consist of the dura mater, arachnoid mater, and pia mater.
• Cerebrospinal fluid is found in the subarachnoid space, between the arachnoid and pia mater which extends around the surface of the brain.

Meningitis

• Meningitis is the inflammation of the subarachnoid space.
• The cerebrospinal fluid contains bacteria, white blood cells, inflammatory proteins, and cellular debris.

Causes of Meningitis

• Meningitis can result from viruses, bacteria, fungi, protozoa, or other factors.
• Viral meningitis is common, mild, and often improves spontaneously.
• Examples of viruses causing meningitis include enteroviruses, influenza, and HSV2.
• Bacterial meningitis requires immediate medical attention.
• Bacteria include N. meningitidis and Streptococcus pneumoniae.
• Rare bacterial causes include Haemophilus influenzae, Listeria monocytogenes, and Mycobacterium tuberculosis.
• Fungi like Cryptococcus neoformans are rare causes usually found in AIDS or cancer patients.
• Protozoa: A rare instance as a result of accidental ingestion of worm eggs or larvae like Angiostrongylus cantonensis.
• Other causes encompass drugs, trauma, neurosurgery, and cancer.

Bacterial Meningitis

• Bacterial meningitis is preceded by nasopharyngeal colonization.
• 10-20% of young adults are colonized with N. meningitidis.
• Bacteria enter the subarachnoid space.

Symptoms of Meningitis

• Inflammation of the meninges results in headache, photophobia, and neck stiffness.
• Systemic inflammatory responses lead to fever, drowsiness, and septic shock.
• Rash is a sign of Neisseria meningitidis.

Diagnosing Meningitis

• Meningitis diagnosis involves clinical suspicion.
• Symptoms may appear late in the illness.
• Samples include cerebrospinal fluid, blood cultures, throat swab, and PCR testing for bacterial DNA.
• Kernig's sign involves lifting the legs slowly, indicating meningitis if sore hamstrings are present.

Cerebrospinal Fluid

• Cerebrospinal fluid is obtained via lumbar puncture.
• In bacterial meningitis, glucose levels decrease, protein and WBC levels increase, cells are neutrophils, and Gram stain and culture tests may be positive.
• In viral meningitis, glucose is normal, protein may be normal or increased slightly, WBC levels increase slightly, cells are lymphocytes, and Gram stain and culture tests are negative.
• Lumbar puncture involves passing a needle between spinous processes into the subarachnoid space below the spinal cord.

Meningococcal Disease

• Meningococcal disease is an infection caused by Neisseria meningitidis.
• There was a disease epidemic during the 1990s.
• Cases often occur in winter.
• It is especially prevalent in young Māori and Pacific children.
• Meningococcal disease can be deadly.

Management of Bacterial Meningitis

• Management includes giving IV antibiotics, resuscitation efforts, and taking blood cultures when the IV line is placed.
• Transfer to a hospital setting.
• Pain relief, fluids, IV antibiotics and droplet precautions are also required.

Management of Viral Meningitis

• Reassurance, analgesia, and rest at home are required.

Sepsis

• Infections such as N. meningitidis or appendicitis can lead to sepsis.
• Sepsis triggers a systemic response involving lipopolysaccharides in the bacterial cell wall interacting with human cells.
• Bacterial cell wall has lipopolysaccharide which is a substance foreign to the human body.
• Lipopolysaccharide and other bacterial components interact with human cells like endothelial cells, platelets, and white blood cells via toll-like receptors.
• Phagocytes engulf and kill bacteria.
• Human cells triggered by bacterial components release cytokines such as interferon, tumor necrosis factor, and interleukins.
• Cytokines induce changes in neighboring vessels, attracting immune cells to the infection site (chemotaxis).
• Spaces open up between endothelial cells, which express proteins like P-selectin, making them stickier.
• Neutrophils bounce along the endothelium, squeezing through gaps between epithelial cells (diapedesis) to move towards the infection site (chemotaxis).
• Antibodies bind to bacterial sugars and proteins, stimulating human immune cells.
• A complement cascade is triggered by antibodies and bacterial components.
• Activated complement enhances chemotaxis, forms spontaneously on the surface of bacteria, opsonizes bacteria for increased immune recognition, and creates holes in bacterial cell walls to kill the bacteria.
• Vasodilation increases blood flow for oxygen, nutrients, and immune cells.
• If infection worsens, further vasodilation occurs and may lead to shock, reduced blood pressure, tachycardia, and reduced organ perfusion.

Shock in Sepsis

• High bacterial load and a fully activated immune system can cause neutrophils to release their DNA into small blood vessels.
• DNA is sticky, trapping bacteria, red blood cells, and platelets.
• Small blood vessels in organs become clogged which leads to decreased blood flow and oxygenation.

Sepsis Symptoms

• Fever, drowsy state, confusion and agitation.
• Increased breathing rate and reduced urine output.
• Low blood pressure with skin grey and cold, and aches.

Management of Septic Shock

• Septic shock is an emergency.
• Mild cases have a mortality rate of 10-15%.
• Mortality increases to 40-50% with organ failure.
• Treatment goals are to maintain organ function and resolve the infection.
• Management includes IV fluids and oxygen.
• Antibiotics, surgery are also management.
• Early recognition is essential.