1. Introduction To Infection Flashcards
What is an infection?
Invasion of a host’s tissues by micro organisms
What is disease caused by?
Disease caused by:
• microbial multiplication
• toxins
• host response
How do people get infections?
- From the source
- From an intermediary from the source
- From the patient themselves
- From the environment from the source
- From animals
What is microbiota?
Microbiota = “commensals”
Microorganisms carried on the skin and mucosal surfaces.
- Normally harmless/ beneficial unless transferred to other sites (can become harmful)
How do patients get infections from themselves?
• transfer to other sites can be harmful - An example would be cystitis where bacteria from the bowel is transferred into the bladder resulting in discomfort and pain during urination
What is the advantage of microorganisms that exist on people normally?
- can provide vitamins
- prevent invasion by more dangerous pathogens
- bacterial colonisation of newborn infants acts as a powerful stimulus for the immune system
How do people get infections from the source and intermediary.
Contact and intermediary may be infected or colonised.
• Physical contact required for some infections, e.g. sexually transmitted infections
• Airborne spread may be sufficient for other infections, e.g. chickenpox
• Vector may be necessary, e.g. mosquito for malaria
What role does the environment play in the infection of a patient?
- Transmission due to ingestion of contaminated food or water
- Inhalation of air contaminated by environmental organisms
- Contact with contaminated surfaces, including medical devices
What are the two types of transmission?
Horizontal
Vertical
What are the 3 types of horizontal transmission?
- contact
- inhalation
- ingestion
What are the 3 types of contact transmission?
- direct
- indirect e.g the touching of a contaminated surface
- vectors e.g malaria from mosquitos
What are the two types of inhalation transmission
- droplets e.g coughs andsneezes
* aerosols - remains suspended until the air for hours - e.g. chicken pox
What is vertical transmission?
mother to child, before or at birth - e.g. HIV transmitted through breast milk
How do microorganisms cause disease?
- Exposure
- Adherence
- Invasion
- Multiplication
- Dissemination
What are the two determinants of disease?
Pathogen and patient
How is the pathogen a determinant of disease?
- virulence factors
- inoculum size - amount of microorganism present
- antimicrobial resistance
What are examples of virulence factors? What are the two main types?
Exotoxins: active secretions of microorganisms that cause direct cellular damage
- cytolytic
- AB toxins
- superantigens
- enzymes
Endotoxins: components of the microorganisms (e.g. antigens) which cause cellular damage by activation of inflammatory response.
What are exo/endotoxins? How to do they work?
Exotoxins = synthesis by microorganisms specifically to be released into host environment. Directly damages hosts cells or disrupts host cell metabolism.
Endotoxins = lipopolysaccharides. Elicits strong immune response in host (too much) leading to sepsis. Not intended to be released out of microorganism, but host are specifically able to recognise them
- indicate infection
What is the 2 types of host cellular damage
- Direct(caused by the pathogen)
- Consequent to host immune system (immune system into overdrive and causes more damage)
How is the patient a determinant of disease?
- site of infection
- co-morbidities - people with chronic diseases are more susceptible to infection. E.g diabetes, cancer, rheumatoid arthritis(immunosuppressants)
What are the questions to answer to know if a patient has an infection?
- Is there an infection?
- Where is the infection?
- What is the cause of the infection?
- What is the best treatment?
How do we know if a patient has an infection?
History: - symptoms • focal, systemic • severity • duration - potential exposures -(where have they been, with whom, doing what, any animals)
Examination:
- organ dysfunctions
Investigations:
- specific
- supportive
What are supportive investigations?
Give evidence towards the probability of an infection being present
• Full blood count – neutrophils, lymphocytes
• C-reactive protein (CRP)
• blood chemistry – liver and kidney function tests
• imaging – x-ray, ultrasound, magnetic resonance imaging (MRI)
• histopathology
What is the difference between haematologous and contiguous spread
H- microorganism in blood stream causing widespread infection (tissue trophisms, microorganism may have preference to certain tissues to grow)
C- spreading locally in a direct growth from site
Give the 2 types of specific investigation that can be used to determine the exact type of bacteria involved in the infection
- Bacteriology - aim to identify organism
2. Virology
How can bacteriology be used to determine the exact type of pathogen present?
• Specimen types
- swabs, fluids, tissues
• "M,C&S": • microscopy - bacterial cells (e.g.Gram stain) - patient cells e.g. cerebrospinal fluid (CSF) • culture • antibiotic susceptibility
- Antigen detection (immunological tests)
- Nucleic acid detection
What are focal symptoms?
In a specific area, unlike systemic symptoms
How can virology be used to detect the exact pathogen causing the disease?
- antigen detection (the virus)
- antibody detection (the patient’s response)
- detecting viral nucleic acid (DNA or RNA)
Difference btwn supportive and specific investigations?
Specific - ID name of organism
Supportive - support probability that infection is at a particular site
Who is involved in managing
infections?
• All clinicians encounter patients with infections • Specialities whose primary interest is infection: infectious diseases medical microbiology and virology genitourinary medicine health protection
What does norovirus cause?
viral gastroenteritis
Define zoonosis.
A disease that can be transmitted to humans from animals.
Give an example of a zoonosis.
- Rabies.
- toxocara (animals contaminate environment)
What is horizontal transmission?
Transmission of infections between members of the same species that are not in a parent-child relationship
What is vertical transmission?
From mother to child
- before or at birth
How can vertical transmission occur before birth?
If membrane surrounding fetus as its developing in the uterus get ruptures, or if there is holes, microorganisms can ascend into the amniotic fluid.
What are acute phase proteins?
Acute-phase proteins are a class of proteins whose plasma concentrations increase or decrease in response to inflammation. - e.g. C reactive protein
