Infection Tests Flashcards
System specific infection symptoms
Cough (respiratory) Neck stiffness (CNS) Bony pain (orthopaedic) Skin pain/redness (skin and soft tissue) Dysuria (urinary)
Non-specific infection symptoms
Fever/ “burning up”
Shaking episodes/chills
Sweating/night sweats
Feeling muddled/confused
Social history regarding infection
To help identify potential pathogens
Travel (inside or outside UK with details if outside UK)
Occupation (farmer, fishmonger, vet, air steward etc.)
Animal contact (which animals)
Hobbies/pasttimes
Sexual history
System specific signs of infection
Lung crackles (respiratory) Meningism (clinical syndrome of headache, neck stiffness, and photophobia, often with nausea and vomiting) (CNS) Bony tenderness (orthopaedic) Skin erythema (SST) Loin tenderness (urinary)
Non-specific signs of infection
Pyrexia
Witnessed rigor/chills
Sweating
Confusion
FBC findings in bacterial infection
Possible anaemia if chronic
Raised WCC (can be low in severe sepsis)
Normal or low lymphocytes
Raised neutrophils
FBC findings in viral infection
Possible anaemia if chronic
Normal WCC (can be low in severe sepsis)
Raised lymphocytes
Normal neutrophils
Normal C-reactive protein
<5mg/l
Raised in infection
Normal procalcitonin
<0.5μg/l
Reasons to use testing
To improve outcome
To provide epidemiological data
Otherwise testing should not be used
What does serology test for?
An antibody response
Direct detection
Detection of a whole organism, antigen or genomic material
Principles of culturing
Isolation of viable pathogen enables:
Identification (immediate or by further testing)
Typing (to establish organism relatedness)
Sensitivity testing (to direct antimicrobial therapy)
Not applicable to non cultivable microorganisms
Needs to be done before antibiotics are started
Gram-negative stain colour
Pink (or colour of counter-stain)
Gram-positive stain colour
Purple
Principle of sensitivity testing
Requires viable microorganisms (usually bacteria or fungi)
Culture of microorganism in presence of antimicrobial agent
Work out if the concentration of antimicrobial that will be available in the body is high enough to kill the microorganism
Solid or liquid media
Uses of sensitivity testing
To inform decisions on targeted antimicrobial therapy (initial treatment is usually empiric, with subsequent being targeted)
Limitations of sensitivity testing
Correlation between antimicrobial sensitivity and clinical response is not absolute
Uses of culture
Establishes the presence of a microorganism at a specific site
Allows the use of empiric and targeted antimicrobial therapy
Provides epidemiological and typing information
Limitations of culture
Is usually slower than direct detection (days)
Principles of direct detection
Detection of whole organism via microscopy or detection of component of organism, via antigen or nucleic acid
Uses of direct detection
Establishes the presence of a microorganism at a particular site (both cultivable and non-cultivable)
Allows the use of appropriate empiric antimicrobial therapy
Is usually the fastest diagnostic method
Limitations of direct detection
Does not give any information on antimicrobial susceptibility or typing
Principle of immunological tests
Detection of immune response to infection
Antibody detection:
IgM
Seroconversion (change from negative to positive result in subsequent tests)
Fourfold rise in titre
