introduction To Infection Flashcards
What is an infection
The invasion of a host’s tissues by micro-organisms
Disease can be caused by microbial multiplication, toxins and host response
How do people get infections
Environment (water, food, air, surfaces)
A lot of infections are caused by patients own microbial system - they get in the wrong place (e.g. UTI) - microorganisms on skin and mucosal surface are usually harmless but transfer to other sites can be
Animals could also be another way that a pathogen is transported from the surrounding environment to the patient or leave something in the surrounding environment that is picked up by the patient
A lot of people who carry pathogen around will never have disease as a consequence of that
Physical contract required for some infections e.g. sexually transmitted infections
Airborne spread may be sufficient for other infections e.g. chicken pox
A vector or host may be necessary e.g. mosquito for malaria
Transmission due to ingestion of contaminated food/ water
Inhalation of air contaminated by environmental organisms
Contact with contaminated surfaces including medical devices
Modes of horizontal transmission Contacts - direct, indirect, vectors Inhalation - droplets and aerosols Ingestion - faecal to oral transmission Vertical transmission - mother to child before or at birth
How do micro-organisms cause disease
Continuous spread - spreading locally via direct transmission
Haematology spread - spreading via blood
Tissue to trophism - disease prefers a specific type of tissue to divide in
E.g. enters viruses
Battle between host and bacteria for survival
Micro-organism will adhere to cell wall of cells, then will invade the cells and use the nutrients in the cell to multiply.
Once they have exhausted the nutrient in the cell, it dies, and releases the microorganisms that go and infect other cells in the body
Exotoxins are ‘meant’ to be released by microorganisms in order to aid their invasion of the host organism
e.g. cytolytic, enzymes and superantigens
Endotoxins - are not intended to be released by the microtoxins - but its what the host cell recognises has host cell invasion
e.g. for gram negative bacteria our body can sense the Lipopolysaccaride cell wall - our body reponds to this
Disease determinants
Factors that affect the pathogen - its virulence factors, inoculum size (substance containing pure bacteria to start a new bacteria culture) and antimicrobial resistance
Factors that affect the patient - where the site of infection is and co-morbidities (as you get older you are more likely to pick up chronic conditions)
How do we know patients have an infection
Questions to ask? • Is there an infection? • Where is the infection? • What is the cause of the infection? • What is the best treatment?
How to check if they have an infection
Take a history - checking for symptoms, looking at severity, duration, potential exposures areas that have a higher risk of containing the disease
Do an examination of the patient - looking at organ dysfunctions - e.g. if patients has HEP C, look to see if patient is yellow to check for jaundice indicatiing liver failure
Carry out investigations - specific and supportive
Supportive investigations
Check for - Full blood count - neutrophils, lymphocytes C-reactive protein (CRP) blood chemistry X ray imaging and MRI
Bacteriology
Specimen types - swabs, fluids, tissues
MCS
Microscopy - bacterial cells (e.g. gram stain)
- Patient cells e.g. CSF - lumbar puncture
Culture
Antibiotic susceptibility - antigen detection and nucleic acid detection
Virology
antigen detection - antigens being given off by the virus to check for the virus
Antibody section - by looking for the patients response - if patient is producing specific chemical antibodies that would indicate virus is present
detecting viral nucleic acid (DNA or RNA) - if present in blood or CSF then virus is present
