LECTURE 1.1 INTRODUCTION TO INFECTION BLOCK

Microorganisms Causing Disease

• Bacteria, viruses, fungi, protozoa, helminths (worms), and prions can cause disease

Transmission of Infection

• Person to person: influenza, SARS-CoV-2, EBV, HIV
• Water: cholera, Hepatitis A
• Food: E. coli, salmonella
• Insects: Malaria
• Surface: MRSA

History Taking

• Importance of taking detailed history:
  • Symptoms
  • Time since first exposure
  • Contacts (including sexual partners, animals)
  • Environment (damp building, air conditioner, overcrowding)
  • Food/drink
  • Travel

Markers of Infection

• Rise in temperature (in some cases, temperature may go down)
  • Interleukin 1 tells the brain to increase the temperature
• General malaise (lethargy, body ache, head ache, loss of appetite, influenza, etc.)
• Pain (general muscle pain in many infections, abdominal pain in hepatitis, abdomen tender to touch, etc.)
• Breathlessness (chest infection including pneumonia)
• Local skin changes:
  • Impetigo: blisters and sores on the skin
  • Cellulitis: redness, heat, pain at the site of infection
  • Necrotising fasciitis: deep skin infection
• Cough:
  • Dry cough (e.g., whooping cough)
  • Productive cough: purulent sputum (e.g., tuberculosis)
• Confusion (meningitis, sepsis, etc.)

General Tests for Infection

• White blood cell count: generally increases in infection, but may decrease in some cases (e.g., CD4+ cells in HIV)
  • Interleukin 6 is a cytokine involved in this process
• C-reactive protein: increases in infection and inflammation

Tests for Cause of Infection

• Bacteria:
  • Direct microscopy after staining (Gram stain, acid-fast stain)
  • Blood culture (growth and identification)
  • Swabs (direct staining and microscopy, growth in appropriate medium)
  • Nucleic acid amplification/PCR
  • Antigen tests (e.g., hepatitis)
  • Antibody tests
• Viruses:
  • Detection of antigens using Elisa/immunofluorescence
  • Nucleic acid amplifications/PCR
  • Antibody tests

Investigations for Infection

• X-ray (used in chest infections and TB)
• MRI scan
• CT scan

Public Health and Ethical Issues

• Infection control:
  • General public health measures: masks, hand hygiene, etc.
  • Infection control measures in hospitals and healthcare premises
  • Quarantine: effect on all areas of healthcare, effect on mental health
• Ethical issues:
  • Ethical dilemmas around sexually transmitted diseases
  • Who do you tell? When do you tell? Public health measures and freedom of citizens (SARS-CoV-2)

Vaccines

• Passive immunization:
  • Immunoglobulins from human serum (pooled human immunoglobulin or hyperimmune immunoglobulin)
  • Helpful in patients who have no immunity against that particular organism
  • Does not generate memory - antibodies have to be made again
  • Clears from the patient’s system in a few weeks to months
• SARS-CoV-2 vaccines:
  • Examples: Pfizer, Moderna, Oxford/AstraZeneca, and Johnson and Johnson/Janssen vaccines
  • Different approaches:
    • Lipid nanoparticle mRNA
    • DNA
    • Adjuvanted protein
    • Inactivated virus particles
    • Non-replicating viral vectors
  • More than 100 other vaccines were in early pre-clinical development
• Coronavirus vaccines in general use:
  • Pfizer/BioNTech COVID-19 vaccine
  • Pfizer/BioNTech bivalent COVID-19 vaccine
  • Moderna COVID-19 vaccine
  • Moderna bivalent COVID-19 vaccine
  • Novavax COVID-19 vaccine (Nuvaxovid)

SARS and MERS

• SARS:
  • Caused by SARS-CoV (bats to other animals and people)
  • Symptoms: respiratory problems, dry cough, fever, head and body aches
  • Spread through respiratory droplets from coughs and sneezes
• MERS:
  • Caused by MERS-CoV (direct or indirect contact with infected dromedary camels)
  • Symptoms: fever, cough, and shortness of breath
  • Pneumonia is common, but not always present
  • Gastrointestinal symptoms, including diarrhea, have also been reported
  • Some laboratory-confirmed cases of MERS-CoV infection are reported as asymptomatic