09-11-21 - Making an infection Diagnosis Flashcards
What 3 things does microbiology do in medicine?
1) Diagnostic advice – identifying the infecting organism
2) Treatment advice – Susceptibility test (what antibiotics may be effective)
3) Infection control – Identify clustered organisms over-represented in the community
What are 5 roles of clinical microbiologists?
- Offer high-quality diagnostic tests.
- Provide clinical consultation for patients with suspected infections.
- Assist with interpreting diagnostic test results.
- Advise on treatment for serious infections.
- Manage infection control within the hospital
What are the 4 methods in making a microbiological diagnosis?
1) Direct examination
2) Culture
3) Serology (scientific study of diagnostic examination of blood serum)
4) Molecular
What are the 2 types of direct examination methods?
What are 3 advantages and disadvantages of smear diagnosis?
What are the 3 different kinds of microscopy?
direct stain
gram stain
ziehl neelsen stain
giemsa stain
RSV
TB
What each type be used to check for?
1) Smear diagnosis * Advantages * Rapid * Simple to perform * Cheap * Disadvantages * Not very sensitive * Not very specific * Requires considerable expertise
2) Microscopy
* Light microscopy:
1) Direct stain – can check stool for parasites
2) Gram stain – can check CSF for bacteria
3) Z-N (Ziehl-Neelsen) stain – check sputum for TB (mix of saliva and mucus coughed up from respiratory tract, typically as a result of infection)
4) Giemsa stain – check blood for malaria
- Fluorescent microscopy
1) Respiratory syncytial virus (RSV) diagnosis
2) Bacterial diagnosis of TB
- Electron Microscopy (EM)
1) Virus detection and identification
What are the 2 types of culture methods?
What are 4 advantages and 1 disadvantage of culture diagnosis?
What is 1 advantage and 3 disadvantages of MALFI-TOF?
1) Culture diagnosis • Advantages • More sensitive than a smear • Allows susceptibility testing • Allows rapid presumptive diagnosis • Allows detailed identification
- Disadvantages
- Rendered negative by antibiotics e.e patient taking antibiotics may prevent bugs from growing in the sample
2) MALDI-TOF – mass spectrometer
• Advantages
• Rapid identification of bacteria
- Disadvantages
- Does not provide susceptibilities
- Delayed by slow growth
- Of no value if antibiotics render culture negative
What is serology?
What are 7 different examples of serological techniques?
aggultination
precipitation
complement fixation
vn
elisa
ria
immunofluorescence
What 5 factors can be detected when making a serological diagnosis?
What type of tests are these all?
How can they help us figure out what type of infection this is?
- Serology is the scientific study of diagnostic examination of blood serum
- 7 examples of serological techniques:
1) Agglutination – antibodies clumping tother
2) Precipitation – antibodies may clump together and precipitate out of the solution
3) Complement fixation – complement system is a very potent immune reaction, and complement fixation often indicates bacterial infection
4) Virus neutralization
5) Enzyme linked immunosorbent assay (ELISA) – technique for detection of antigens in blood sample
6) Radioimmunoassay (RIA)
7) Immunofluorescence - Last 2 are labelled antibodies fixing to specific target
- What 5 things can be detected when making a serological diagnosis:
1) Detecting high IgG concentration
2) Detecting rising or falling titres
3) Detect IgM/IgA levels
4) Measure avidity (overall strength) of binding between antibodies and antigens
5) Detecting antigens
- These are all examples of immunological tests (concerning antibodies – immunoglobulins)
- The rising and falling of levels of particular antibodies can give us insight into what is causing the infection e.g bacteria, virus, infection
What are the 2 different types of molecular diagnosis techniques?
What are the 5 different subtypes of the second type?
1) DNA hybridization
2) Nucleic acid amplification testing
* Polymerase Chain Reaction (PCR)
* Ligase chain reaction (LCR)
* Automated DNA amplification
* Real time PCR
What are 5 examples of specimens taken in response to different conditions?
UTI
WOUND
MENINGITIS
PYREXIA
PNEUMONIA
1) Urinary tract infection (UTI) - Midstream urine (MSU) –
2) Wound - Pus or swab
3) Meningitis - CSF and blood
4) Pyrexia of unknown origin (PUO) - Blood for culture + serology
5) Pneumonia - Sputum, lavage (washing out of body cavity with water or medicated solution), serology
What are 3 ways specimens can be classified?
…sought
1) Single pathogen sought
2) Limited multiple pathogens sought
3) Many pathogens sought
How can specimens with a single pathogen be obtained?
What then occurs?
What infections may be found in the specimen?
What will be found in this specimen?
- Specimens with a single pathogen can be obtained through a throat swab (except if diphtheria is suspected – serious infection)
- Infection control screening tests can then occur
- Unusual infections may be found in the sample, such as pertussis
- This method is also useful for MTB (Mycobacterium tuberculosis) detection
- We will find a variety of organisms within this sample, but only one infection-causing pathogen e.g we will only find MTB in a TB specimen, because it is a TB infection
What are 3 examples of specimens where a few pathogens are likely?
spticaemia and bacterarmia
1) CSF
2) STI sample
3) blood
What are 5 examples of specimens with many pathogens?
1) Faeces
2) Abscess pus
3) LRTI samples (Lower respiratory tract infection)
4) Oral swab
5) Urine
What are 3 pieces of evidence of a positive diagnosis?
sensitivity
specifity
PVP/ PVN
How are true positives/negatives obtained?
1) Sensitivity
- The ability of a test to detect all of the true positives
- Equal to the number of positives obtained divided by the total number of positives
2) Specificity
- Ability to identify the number of true negatives
- Equal to the number of negatives obtained divided by the number of true negatives
3) Predictive value of a positive/negative test (PVP/PVN)
* Predictive value for a particular test to get it right or wrong
* Based on Sensitivity/specificity
- True positives/negatives are obtained through very in-depth testing
What are the 3 things that are needed to interpret clinical tests?
1) Test sensitivity and specificity
2) Impact of normal flora on tests
3) The fourth dimension
* Do I need a test?
* Can I get a test?
What must interpretation of microbiology results be made in the context of?
What does a person’s normal flora affect?
Where is normal flora found?
What does the normal flora consist of?
When can normal flora cause health issues?
- The interpretation of all microbiological results must be made in the context of normal flora
- A person’s normal flora will affect how well they are on a day-to-day basic i.e everyone has different flora and will respond differently to the same illness/infection
- Normal flora is found everywhere, except areas such as blood, bladder and CSF, where it is unusual for bacteria to be present
- Many pathogens are also colonisers in the normal flora of the body, and will only cause illness in immunocompromised individuals
When may infections (such as UTIs) not need laboratory diagnosis?
