Theme 3- part 2 Flashcards
If a disease is rare, more likely a false positive or negative?
The risk of false negative and false positive changes with how frequently a disease is seen in the community (and with the quality of a test). In simple terms, if a disease is very rare, a false positive is more likely and should be corroborated with other information
What is sensitivity?
The proportion of people with the disease who have a positive test
A/(A + B)
What is specificity?
The proportion of people without the disease who have a negative test
D/(C + D)
What are M, C and S?
Microscopy culture and sensitivity
What is microscopy?
- Cell count
- Gram stain
- Direct visualisation of organisms
What is culture?
- Difficult culture media
- Slopes
What is sensitivity in terms of M, C and S?
- EUCAST disc testing- use this test organism with antibiotics and see if antibiotic will work
- Strips
Many samples – pus, blood, sputum, urine – are sent for MCS, but what does that mean?
- M - If from a sterile site – joint/CSF – the Gram stain is performed, this is not done for all samples
- C – different culture media are set up based on the likely bacteria causing infection at the site, some are generic, some look for specific groups of organisms e.g. anaerobes, others specific organism – e.g. gonorrhoea in a GU swab- look at what has grown
- S – If a relevant pathogen grows, we will set up sensitivity tests on a plate. This will show which antibiotics are likely to be effective in practice.
What are blood tests for detection for immunity?
- IgG – previous infection
- IgM – current infection (or reactivation)
- Complement fixation tests (being phased out)
What are blood tests for detection of a pathogen?
- Blood culture - M,C & S
- Polymerase chain reaction (PCR)- HIV, Hep C, meningeal coccus or pneumoniae coccus
- Microscopy (malaria) /trypanosomiasis
What are the generic tests?
- Blood cultures
- FBC (look for WBC= inflammation), U&E (to see if renal failure related to sepsis), LFT, CRP (inflammation, clotting, procalcitonin
What are speficifc tests for infections?
- Pus from abscess – culture and sensitivity results
- Hepatitis B serology
- Meningococcal PCR on CSF
What are CNS infections?
- Meningitis – fever, headache, neck stiffness. Sometimes meningococcal or viral rash
- Encephalitis – similar, fever, confusion and sometimes n/v (nausea/vomiting)
- Brain abscess – fever, headache, neurological impact depending on anatomical location, can lead to ventriculitis
What is meningitis/ encephalitis?
Inflammation of the meninges/brain parenchyma
How do we test for meningitis/ encephelitis?
- Radiology – CT head. MRI head (for encephalitis)
- Lumbar puncture – cerebrospinal fluid (CSF)- look at the colour of the flood and test it (turbid- bacteria, clear- normal CSF or viral infection). Look at WBC in CSF to see if viral or bacterial casue (bacterial more neutrophilic and viral more lymphocytic). Exceptions- late reaction is more lymphocytic. Protein and glucose also indicators.
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Treatment for meningitis/ encephalitis?
GIVE BROAD SPECTURM ANTIBIOTICS STRAIGHT AWAY DUE TO THE HIGH MORTALITY. THEN RESULTS OF CSF THEN THEN DECIDE WHAT TO GIVE
What do CSF tests test for in meningitis/ encephalitis?
- Routinely tested for cell count, protein, glucose, MC&S
- Viral PCR (enterovirus, adeno, VZV, HSV, parechovirus)
What are other tests other for CSF if CSF suggests meningitis/ encephalitis?
- Cryptococcal antigen
- Toxoplasma PCR
- TB culture
What are non-CSF tests to test for meningitis/ encephalitis?
- Blood cultures (2 sets)
- Bacterial throat swab
- Blood for HIV and blood PCR (S. pneumoniae, N. meningitidis)
What bacteria if adult has meningitis?
Adults if have meningitis- would have S. pneumoniae or N. meningitidis
Elderly and neonates what bacteria if have meningits/ encephalitis?
Adults if have meningitis- would have S. pneumoniae or N. meningitidis, elderly have listeria, neonates would have Group B strep Agalactiae, E. coli and listeria.
How do you test for meningitis and encephalitis?
- Not LP/CSF- as can cause coning (brain forced out of skull into SC) if high pressure in the brain
- For aspiration/excision- get samples
- Blood cultures
- Fungal/bacterial/parasitic/TB- looking to find if this is cause via blood tests
n brain abscesses, there are a number of mechanisms of infection what are they?
- Severe ENT infection e.g. sinusitis can cause – often streptococcal/anaerobic.
- Infective endocarditis, infection of heart valves- endocarditis- bacterial from heart valves spread around the body, can spread to the brain.
- This can be staph or strep. Also post-operative, this can be a number of different pathogens. LP is not usually appropriate, can cause brain to herniate through the base of the skull.
- Sometimes abscesses are aspirated or excised, then send for MCS. Otherwise rely on blood cultures. In immunocomp – things like toxo are important.
What are symptoms of upper RTIs?
Upper is common cold, sore throats, ear infections
What are symptoms of lower RTIs?
Lower RTI is bronchitis/ pneumonia
Difference between typical and atypical pneumonia?
‘Atypical’ pneumonia – caused by bacteria than the more common one
What is community acquired pneumonia caused by?
Community acquired pneumonia- caused by strep pneumoniae
How do you diagnose typical CAP?
Typical
Blood cultures (if severe)
Sputum for MC&S
How do you diagnose atypical CAP?
‘Atypical’ pneumonia screen if antibiotics failed, features not normal on X-ray, some causes may need other antibiotics
- Sputum for MC&S
- Viral PCR
- Mycoplasma (serology/PCR)
- Chlamydia (PCR)
- Legionella antigen in urine
Cause for atypical pneumonia? What drug is given?
Cause for atypical pneumonia is legionella pneumophilia- won’t respond to co-amoxiclav- suggest to add clartihromycin
Atypical pneumonia may be suspected if what?
- Failure of narrow spectrum antibiotics
- Unusual clinical features – rash/arthralgia
- Radiological features
- Epidemiology – travel
What is the viral name for pneumonia? How is it tested?
- Viral pneumonia/pneumonitis
- Respiratory viral PCR
How long does pulmonary TB take to develop?
Pulmonary TB- can take months/ years to develop
Disease requiring exposure then reactivation.
In addition, not all TB is active, we also detect and treat latent TB as this prevents reactivation in later life. In order to detect patients with TB – we can look at exposure or active infection.
What are the tests for pulmonary TB?
CXR
Exposure testing
- Mantoux- for if you have had close contact with somone like someone you are living with
- IGRA’s (interferon gamma release assay)- T-spot/Quantiferon
Active pulmonary infection
- 3 sputum samples
- 8+ weeks culture
- Whole-genome sequencing
- PCR
Respiratory tract infection in the immunocompromised host- fungal infection what are you likely to be susceptible to?
- Aspergillus fumigatus infection
- Cryptococcosis
- Mucormycosis
Respiratory tract infection in the immunocompromised host- bacterial infection what are you likely to be susceptible to?
- Nocardia sp.
- Gram-negatives – resistant
Respiratory tract infection in the immunocompromised host- what other infections are you susceptible to?
- CMV
- HHV6
- Pneumocystis jirovecii
- Non-tuberculous mycobacteria
- Measles
Respiratory tract infection in the immunocompromised host- what non-infective things are you susceptible to?
GvHD
Cryptogenic organising pneumonia
GvHD- graft vs. host disease
Respiratory tract infection in the immunocompromised host what tests are used?
- Bronchoscopy/biopsy samples
- Aspergillus/CMV blood tests
Skin and soft tissue infection- whata re the localised symptoms?
- Impetigo- crusting- spots on face, neck and back
- Erysipelas- deep skin infection
- Cellulitis- superficial skin infection
Skin and soft tissue infection- severe/ extensive symptoms?
Severe/extensive
Necrotising fasciitis- in deep planes of tissue and causes severe sepsis
What other infection can you have from skin and soft tissue infection?
Diabetic foot infection
How do you test for skin and soft tissue infection for localised?
- Wound swabs unhelpful from intact skin
- Blister fluid/pus is better
How do you test for skin and soft tissue infection for severe/ nectrotising fascitis?
- Blood cultures
- MRSA swabs
- Full history
For general skin and soft tissue infection what other tests do you need?
Look for MRSA swabs/status
Request full history - water contact/travel/animal contact
What are the tests for non-infected wounds for diabetic food infection?
- May be ‘weepy’ or ‘smelly’ but this is not evidence of infection
- Swabs may represent colonising flora only
What are the tests for diabetic foot infection for mild infection?
Mild infection
- Moderate/severe – debridement then
- deep sampling of bone/tissue
- Often in theatre
What are the symptoms of lower UTIs?
Lower UTI- cystits, dysuria, frequency and urgency
Symptoms of upper UTIs?
Upper UTI- renal angle pain, vomiting, fever