Past papers 5 Flashcards
OSPACE example questions
Examine this Quality Control Chart (6 min)
a. What abnormality is shown in this quality control chart?
b. Which rule has been violated and how?
c. Give two possible scenarios which may account for this abnormality.
Westgard rules
Abnormality -
change in quality control batch
inappropriate storage of quality controls - temperature
inadequate maintenance of instrument
calibration errors
OSPACE example questions
Examine these electron-micrographs (6 min)
a. In which clinical specimen type can you find all these viruses?
b. Name the viruses labelled A to G.
c. Which of these viruses belong to the same viral family? Name the family.
d. Which of these viruses have effective vaccines? What is t
he nature of this
vaccine?
Examine all EM pictures
A. Faeces
B. EM - 7 viruses. Possibly 5x GI viruses, plus CMV/ EBV
C. Caliciviridae - Noro/ Sapo
D. Rotavirus - live attenuated oral vaccine, children 8/12 weeks.
Adenovirus has live vaccine against types 4/7 - this is orally adminsitered. Only uses for military USA. Only for respiratory infections
OSPACE example questions
Examine this phylogenetic tree (6 min)
a. Does this phylogenetic tree support transmission of hepatitis C in the
dialysis unit? Why do you say so and which patients were involved?
b. Can you determine which patient is th
e index case from this tree? Why do
you say so?
c. What is the meaning of the number at the node of each branch?
Read phylogenetic tree flashcards
Nodes at each branch - the number is usually between 0 and 1.
A high value means that there is strong evidence that the sequences to the right of the node are correct
OSPACE example questions
These pictures are from different patients suffering different
complications of the same viral infection (6 min)
a. Which virus caused these complications?
b. Name each complication.
c. Name four other possible complications of this viral infection?
Not sure
Adenovirus?
conjunctivitis
Encpehalitis
Pneumonitis
Hepatitis
Gastroenteritis
Haemorrhagic cystitis
Enterovirus
Haemorrhagic conjunctivitisis
Meningitis
Myocarditis
Hand foot and mouth
Herpangina
OSPACE example questions
This is the histological examination of brain tissue of a man died of an unexplained encephalopathy (6 min)
a. What is the diagnosis?
b. What is the pathognomonic feature found in the histology slide?
c. How do you diagnose this condition before death?
? HSV encephalitis
necrosis of medial temporal lobe/ frontal lobe
OSPACE example questions
This is the brain MRI of a patient from sub-Saharan Africa who
presented with a two week history of headache and admitted with generalised seizures (6 min)
a. What is the most likely diagnosis?
b. Name one possible alternative diagnosis.
c. What is the most likely underlying condition?
d. What is the management of this condition?
HIV
?cysticercosis - most common cause seizures worldwide. Pork tapeworm
Toxoplasma
Malignancy e.g Lymphoma
Viral encephalitis
OSPACE example questions
8.
Examine these clinical pictures (6 min)
a. Which two viral infections were demonstrated in these clinical pictures?
b. Name the signs found in the oral cavity and match each one to its
corresponding clinical picture.
c. What laboratory methods are available to diagnose these two infections?
?EBV - oral hairy leukoplakia
PCR and histology + IHC
?HHV8 - Kaposi sarcoma
PCR and histology + IHC
OSPACE example questions
Examine these monolayer cell culture inoculated with respiratory
sample from a patient (6 min)
a. Describe the morphology of the cells.
b. Describe the cytopathic effect observed
c. What viruses could be growing in this cell monolayer with this cytopathic effect?
?RSV
cytopathic effect -
enlarged multinucleated cells with cytoplasmic inclusions - syncytium
syncytium infection -
RSV
Covid
HSV
VZV
EBV
CMV
HIV
typically enveloped viruses that cause cell fusion
OSPACE example questions
Examine this HIV protease and reverse transcriptase sequence and
the report? (10 min)
a. What mutations are shown?
b. What are the clinical significances?
c. Recommend a suitable treatment regimen for this patient
Learn common mutations
Learn which drugs to switch to
probably switch:
2x NRTI + PI to
2x NRTI + INT
Probably switch NNRTI to NRTI
OSPACE example questions
A nucleic acid amplification test for Chlamydia trachomatis
has a claimed sensitivity of 99.9% and a specificity of 99.9% for self-
taken vulvo-vaginal swab in women (7 minutes)
It is applied to two different populations, screening 10,000 individuals in each group:
Population A:
Sexually active female teenagers (prevalence 1 in 100)
Population B:
Asymptomatic women > 40 years old (prevalence 1 in 1000)
A 2x2 table has been completed for population A
Test pos: 100 TP /1 TN aka false pos Total: 101
Test neg: 0 TP aka false neg / 899 TN Total: 899
Total: 100 TP / 900 TN Total: 1000
Draw out 2x2 table
What is the PPV for the test in population A?
The positive predictive value is the probability that following a positive test result, that individual will truly have that specific disease.
PPV = TP/ TP + FP
PPV = 100 TP/ 100 TP + 1 FP
PPV = 100/ 101 = 99%
OSPACE example questions
A nucleic acid amplification test for Chlamydia trachomatis
has a claimed sensitivity of 99.9% and a specificity of 99.9% for self-
taken vulvo-vaginal swab in women (7 minutes)
It is applied to two different populations, screening 10,000 individuals in each group:
Population A:
Sexually active female teenagers (prevalence 1 in 100)
Population B:
Asymptomatic women > 40 years old (prevalence 1 in 1000)
A 2x2 table has been completed for population A
Test pos: 100 TP /1 TN aka false pos Total: 101
Test neg: 0 TP aka false neg / 899 TN Total: 899
Total: 100 TP / 900 TN Total: 1000
Draw out 2x2 table
What is the NPV for the test in population A?
The negative predictive value is the probability that following a negative test result, that individual will truly not have that specific disease.
NPV = TN/ TN + FN
NPV = 899 TN/ 899 + 0 FN
NPV = 100%
OSPACE example questions
A nucleic acid amplification test for Chlamydia trachomatis
has a claimed sensitivity of 99.9% and a specificity of 99.9% for self-
taken vulvo-vaginal swab in women (7 minutes)
It is applied to two different populations, screening 10,000 individuals in each group:
Population A:
Sexually active female teenagers (prevalence 1 in 100)
Population B:
Asymptomatic women > 40 years old (prevalence 1 in 1000)
A 2x2 table has been completed for population A
Test pos: 100 TP /1 TN aka false pos Total: 101
Test neg: 0 TP aka false neg / 899 TN Total: 899
Total: 100 TP / 900 TN Total: 1000
Draw out 2x2 table
Calculate the same table for population B
- Sensitivity is the ability to detect the true positives ie not falsely assigning them to false neg (C), specificity is the ability to detect the true negatives, if neither of these are 100% then you may get some false negatives and false positives.
- Positive predictive value is likelihood that positive test = true positive ie A/(A+B)x100.
- If the prevalence of infection is 1 in 1000 then in 10,000 there should be 10 true positives. If the sensitivity is 99.9% then if you test those 10 true positives you will be right 99.9% of the time, 0.1% of 10 is so small that 0 goes in C. So I think all of the true positives will be detected and correctly assigned to A.
- If the prevalence is 1 in 1000 then in 10,000 there should be 9990 true negatives. If specificity is 99.9%, then you will be wrong 0.1% of the time. 0.1% of 9990 is 10. So I think that 9980 of your 9990 will be correctly assigned as negative and 10 will be incorrectly assigned as positive (B).
I reckon the PPV is therefore 10/20x100 = 50%.
True pos/ Test pos 10 (A)
True pos/ Test neg 0 (C)
True neg/ Test pos 10 (B)
True neg/ Test neg 9980 (D)
Test pos total - 20
Test neg total - 9980
OSPACE example questions
Explain the difference between positive predictive values between populations between A + B
For any given test (i.e. sensitivity and specificity remain the same) as prevalence decreases, the PPV decreases because there will be more false positives for every true positive. This is because you’re hunting for a “needle in a haystack” and likely to find lots of other things that look similar along the way – the bigger the haystack, the more frequently you mistake things for a needle.
Therefore, as prevalence decreases, the NPV increases because there will be more true negatives for every false negative. This is because a false negative would mean that a person actually has the disease, which is unlikely because the disease is rare (low prevalence).
OSPACE example questions
You are asked to set up a multiplex real time PCR for influenza viruses.
1.1.List the basic reagents required in a real time PCR reaction.
PCR
6 main components:
DNA template
primers
nucleotides
enzymes - DNA polymerase (Taq polymerase) or reverse transcriptase
reaction buffer - magnesium
fluorescent probes for real-time PCR - e.g SYBR green
OSPACE example questions
You are asked to set up a multiplex real time PCR for influenza viruses.
1.2.Explain the mechanism of action of a dual-labelled probe in real time PCR.
Dual labeled probes used in quantitative real-time PCR systems take advantage of the 5’ -> 3’ exonuclease activity of Taq polymerase.
Dual labeled probes contain a 5’ fluorescent reporter and a 3’ quencher which anneals between the PCR primers.
During the extension phase of PCR, the 5’ -> 3’ exonuclease activity of Taq polymerase cleaves the fluorescent reporter from the probe. The amount of free reporter accumulates as the number of PCR cycles increases.
The resulting, detectable fluorescence signal is proportional to the amount of accumulated PCR product - this provides real-time analysis
