INFECTIOUS DISEASE
Questions&Answers
Q-1
A 62 year old IV drug abuser is brought into the emergency department with
complaint of fever, shivering, malaise, shortness of breath and productive cough.
Around 8 days ago he developed symptoms consistent with a flu-like illness.
Initially there was an improvement in his condition but deteriorated over the past
three days. He now has a temperature of 39 C, a pulse of 110 beats/minute, a
blood pressure of 100/70 mmHg and a respiratory rate of 22 breaths/minute. A
chest x-ray shows bilateral cavitations. What is the SINGLE most likely causative
organism?
A. Mycoplasma pneumoniae
B. Staphylococcus aureus
C. Chlamydia pneumoniae
D. Eschericia coli
E. Klebsiella pneumoniae
ANSWER:
Staphylococcus aureus
EXPLANATION:
Staphylococcus aureus may complicate influenza infection and is seen most frequently
in the elderly and in intravenous drug users or patients with underlying disease. Chest
x-ray shwos bilateral cavitations. Remember, there is a high incidence of
Staphylococcus aureus pneumonia in patients following influenza so in PLAB if you see
a patient with a flu-like illness which symptoms are now of pneumonia, the likely
causative organism is Staphylococcus aureus.
Q-2
A 28 year old man presents with a widespread maculopapular rash over his soles
and palms. He also has mouth ulcers. He had a penile ulcer which healed six
weeks ago. What is the SINGLE most likely organism responsible?
A. Mycoplasma genitalium
B. Treponema pertenue
, C. Treponema pallidum
D. Lymphgranuloma venereum
E. Herpes simplex virus type 2
ANSWER:
Treponema pallidum
EXPLANATION:
Syphilis
Syphilis is a sexually transmitted infection caused by the spirochaete Treponema
pallidum. Acquired syphilis is characterised by primary, secondary and tertiary stages.
The incubation period is around 3 weeks.
Acquired syphilis
Primary features
• Chancre - painless ulcer at the site of sexual contact
• Local non-tender lymphadenopathy
• In women, they are found on the vulva, labia and, much less frequently, on the cervix.
Secondary features
• Secondary syphilis often appears 6 weeks after the beginning of the primary lesion but
may overlap or not appear for several months.
• Systemic symptoms: fevers, lymphadenopathy, headaches, malaise.
• A generalised polymorphic rash often affects the palms, soles and face
• Papules enlarge into condylomata lata (pink or grey discs) in moist warm areas.
Tertiary features
• Gummas (granulomatous lesions → can occur in any organ but most commonly affect
bone and skin)
• Cardiovascular syphilis → ascending aortic aneurysms, aortic regurgitation
• Neurological syphilis → tabes dorsalis, dementia
Q-3
A 44 year old HIV positive man complains of a two week history of worsening
headache, facial weakness and visual hallucinations. He also reports new onset
of eye pain. An MRI head reveals multiple ring shaped contrast enhancing
lesions. What is the SINGLE most likely causative organism?
A. Cytomegalovirus
B. Streptococcus
C. Toxoplasma gondii
D. Herpes simplex virus
E. Pneumocystis jirovecii
ANSWER:
Toxoplasma gondii
,EXPLANATION:
The symptoms and MRI findings here are highly suggestive of toxoplasmosis, a disease
caused by the protozoan Toxoplasma gondii.
The reason behind the HIV history is that toxoplasmosis can reactivate in those with
severe HIV disease when their CD4 counts are very low ( <50-100/μL).
Principle Manifestations usually include a brain mass lesion, headache, confusion,
seizures, and focal neurologic deficits. These symptoms occur due to increased
intracranial pressure. In patients with AIDS, cerebral toxoplasmosis should be right at
the top of the list of differentials if one presents with focal neurological symptoms.
Imaging such as CT or MRI scan of the head would show a "ring" (contrast) enhancing
lesion with oedema. Scans may show solitary lesions or cortical atrophy. Given the
choice of imaging modality, choose an MRI over a CT as MRI appears to be more
sensitive than CT in imaging for cerebral toxoplasmosis.
TOXOPLASMOSIS
Toxoplasma gondii is a protozoa which infects the body via the gastrointestinal tract,
lung or broken skin. Human infection occurs from consumption of undercooked meat
or, foot or water contaminated with the oocytes. It's oocysts release trophozoites which
migrate widely around the body including to the eye, brain and muscle. The usual
animal reservoir is cats where oocytes are produced in the cat’s intestines and shed in
its faeces.
Interestingly, toxoplasma gondii is known to remove rats’ fear of cats. Somehow
infected rats are mildly attracted to the odour of cats which uninfected rats would usually
run away from. This is thought to be an evolutionary adaptation to help toxoplasma
gondii complete its life cycle: rats are exposed to cat faeces and are infected with
toxoplasma gondii. They then lose their innate fear of cats and are more likely to be
eaten by cats. Toxoplasmosis then sexually reproduces in the rat’s gut. This brings
new meaning to the term “Eat PrEy, Love”.
Most infections are asymptomatic. Symptomatic patients usually have a self-limiting
infection, often having clinical features resembling infectious mononucleosis (fever,
malaise, lymphadenopathy). Other less common manifestations include
meningoencephalitis and myocarditis.
Treatment:
Pyrimethamine plus sulphadiazine
Q-4
A 25 year old man was admitted to the hospital with a fever of 38.8 C and rigors.
He complains of a three day history of general malaise, mild headaches,
arthralgia and myalgia. He especially complained of bilateral calf pain. His past
history is significant for a trip to the Caribbean from which he returned five days
, ago. He describes the trip to the Caribbean with his friends as being amazing and
describes a host of activities such as swimming, hiking and fishing. Upon further
questioning, he also revealed that he noticed a red discoloration of his eyes
before they turned to yellow. The patient also mentions seeing “spots” on his
skin. On physical examination, the patient appears to be jaundiced. Abdominal
examination revealed generalised abdominal tenderness.
His vitals are as follows:
Blood pressure 98/56 mmHg
Heart rate 122 beats per minute
Respiratory rate 18 breaths per minute
Oxygen saturation on room air 98%
Blood tests were done and the laboratory results are as follows:
Alanine transferase (ALT) 89 U/L (5-35 U/L)
Aspartate transaminase (AST) 60 U/L (5-35 U/L)
Alkaline phosphatase (ALP) 162 U/L (30-150 U/L)
Gamma glutamyl transferase (GGT) 33 U/L (8-60 U/L)
White blood cells 15 x 109/L (4-11 x 109/L)
Platelets 180 x 109/L (150-400 x 109/L)
What is the SINGLE most appropriate investigation in this scenario to confirm the
diagnosis?
A. Unconjugated bilirubin
B. Paul Bunnell test
C. Blood and urine culture and sensitivity
D. CSF analysis
E. ELISA for IgM antibodies
ANSWER:
Blood and urine culture and sensitivity
EXPLANATION:
This patient is suffering from leptospirosis. Leptospirosis is the most widespread
zoonotic infection worldwide. The main risk factor for acquiring the infection is direct or
indirect contact with the urine of infected animals. Contact can occur secondary to
occupational exposure or accidentally via exposure to unclean sources of water.
Travelers and athletes participating in water sports, such as those who compete in
triathlons, represent a growing population at risk. In the UK, ask for a history of rowing,
fishing, contact with animals or travel. The red discoloration of the eye seen initially is
subconjunctival haemorrhage which occurs in more than 90% of patients with
leptospirosis. Aminotransferase levels are usually elevated but they are rarely higher
than 200 U/L just as seen in this stem.
The single most appropriate investigation in this scenarior would be blood and urine
Questions&Answers
Q-1
A 62 year old IV drug abuser is brought into the emergency department with
complaint of fever, shivering, malaise, shortness of breath and productive cough.
Around 8 days ago he developed symptoms consistent with a flu-like illness.
Initially there was an improvement in his condition but deteriorated over the past
three days. He now has a temperature of 39 C, a pulse of 110 beats/minute, a
blood pressure of 100/70 mmHg and a respiratory rate of 22 breaths/minute. A
chest x-ray shows bilateral cavitations. What is the SINGLE most likely causative
organism?
A. Mycoplasma pneumoniae
B. Staphylococcus aureus
C. Chlamydia pneumoniae
D. Eschericia coli
E. Klebsiella pneumoniae
ANSWER:
Staphylococcus aureus
EXPLANATION:
Staphylococcus aureus may complicate influenza infection and is seen most frequently
in the elderly and in intravenous drug users or patients with underlying disease. Chest
x-ray shwos bilateral cavitations. Remember, there is a high incidence of
Staphylococcus aureus pneumonia in patients following influenza so in PLAB if you see
a patient with a flu-like illness which symptoms are now of pneumonia, the likely
causative organism is Staphylococcus aureus.
Q-2
A 28 year old man presents with a widespread maculopapular rash over his soles
and palms. He also has mouth ulcers. He had a penile ulcer which healed six
weeks ago. What is the SINGLE most likely organism responsible?
A. Mycoplasma genitalium
B. Treponema pertenue
, C. Treponema pallidum
D. Lymphgranuloma venereum
E. Herpes simplex virus type 2
ANSWER:
Treponema pallidum
EXPLANATION:
Syphilis
Syphilis is a sexually transmitted infection caused by the spirochaete Treponema
pallidum. Acquired syphilis is characterised by primary, secondary and tertiary stages.
The incubation period is around 3 weeks.
Acquired syphilis
Primary features
• Chancre - painless ulcer at the site of sexual contact
• Local non-tender lymphadenopathy
• In women, they are found on the vulva, labia and, much less frequently, on the cervix.
Secondary features
• Secondary syphilis often appears 6 weeks after the beginning of the primary lesion but
may overlap or not appear for several months.
• Systemic symptoms: fevers, lymphadenopathy, headaches, malaise.
• A generalised polymorphic rash often affects the palms, soles and face
• Papules enlarge into condylomata lata (pink or grey discs) in moist warm areas.
Tertiary features
• Gummas (granulomatous lesions → can occur in any organ but most commonly affect
bone and skin)
• Cardiovascular syphilis → ascending aortic aneurysms, aortic regurgitation
• Neurological syphilis → tabes dorsalis, dementia
Q-3
A 44 year old HIV positive man complains of a two week history of worsening
headache, facial weakness and visual hallucinations. He also reports new onset
of eye pain. An MRI head reveals multiple ring shaped contrast enhancing
lesions. What is the SINGLE most likely causative organism?
A. Cytomegalovirus
B. Streptococcus
C. Toxoplasma gondii
D. Herpes simplex virus
E. Pneumocystis jirovecii
ANSWER:
Toxoplasma gondii
,EXPLANATION:
The symptoms and MRI findings here are highly suggestive of toxoplasmosis, a disease
caused by the protozoan Toxoplasma gondii.
The reason behind the HIV history is that toxoplasmosis can reactivate in those with
severe HIV disease when their CD4 counts are very low ( <50-100/μL).
Principle Manifestations usually include a brain mass lesion, headache, confusion,
seizures, and focal neurologic deficits. These symptoms occur due to increased
intracranial pressure. In patients with AIDS, cerebral toxoplasmosis should be right at
the top of the list of differentials if one presents with focal neurological symptoms.
Imaging such as CT or MRI scan of the head would show a "ring" (contrast) enhancing
lesion with oedema. Scans may show solitary lesions or cortical atrophy. Given the
choice of imaging modality, choose an MRI over a CT as MRI appears to be more
sensitive than CT in imaging for cerebral toxoplasmosis.
TOXOPLASMOSIS
Toxoplasma gondii is a protozoa which infects the body via the gastrointestinal tract,
lung or broken skin. Human infection occurs from consumption of undercooked meat
or, foot or water contaminated with the oocytes. It's oocysts release trophozoites which
migrate widely around the body including to the eye, brain and muscle. The usual
animal reservoir is cats where oocytes are produced in the cat’s intestines and shed in
its faeces.
Interestingly, toxoplasma gondii is known to remove rats’ fear of cats. Somehow
infected rats are mildly attracted to the odour of cats which uninfected rats would usually
run away from. This is thought to be an evolutionary adaptation to help toxoplasma
gondii complete its life cycle: rats are exposed to cat faeces and are infected with
toxoplasma gondii. They then lose their innate fear of cats and are more likely to be
eaten by cats. Toxoplasmosis then sexually reproduces in the rat’s gut. This brings
new meaning to the term “Eat PrEy, Love”.
Most infections are asymptomatic. Symptomatic patients usually have a self-limiting
infection, often having clinical features resembling infectious mononucleosis (fever,
malaise, lymphadenopathy). Other less common manifestations include
meningoencephalitis and myocarditis.
Treatment:
Pyrimethamine plus sulphadiazine
Q-4
A 25 year old man was admitted to the hospital with a fever of 38.8 C and rigors.
He complains of a three day history of general malaise, mild headaches,
arthralgia and myalgia. He especially complained of bilateral calf pain. His past
history is significant for a trip to the Caribbean from which he returned five days
, ago. He describes the trip to the Caribbean with his friends as being amazing and
describes a host of activities such as swimming, hiking and fishing. Upon further
questioning, he also revealed that he noticed a red discoloration of his eyes
before they turned to yellow. The patient also mentions seeing “spots” on his
skin. On physical examination, the patient appears to be jaundiced. Abdominal
examination revealed generalised abdominal tenderness.
His vitals are as follows:
Blood pressure 98/56 mmHg
Heart rate 122 beats per minute
Respiratory rate 18 breaths per minute
Oxygen saturation on room air 98%
Blood tests were done and the laboratory results are as follows:
Alanine transferase (ALT) 89 U/L (5-35 U/L)
Aspartate transaminase (AST) 60 U/L (5-35 U/L)
Alkaline phosphatase (ALP) 162 U/L (30-150 U/L)
Gamma glutamyl transferase (GGT) 33 U/L (8-60 U/L)
White blood cells 15 x 109/L (4-11 x 109/L)
Platelets 180 x 109/L (150-400 x 109/L)
What is the SINGLE most appropriate investigation in this scenario to confirm the
diagnosis?
A. Unconjugated bilirubin
B. Paul Bunnell test
C. Blood and urine culture and sensitivity
D. CSF analysis
E. ELISA for IgM antibodies
ANSWER:
Blood and urine culture and sensitivity
EXPLANATION:
This patient is suffering from leptospirosis. Leptospirosis is the most widespread
zoonotic infection worldwide. The main risk factor for acquiring the infection is direct or
indirect contact with the urine of infected animals. Contact can occur secondary to
occupational exposure or accidentally via exposure to unclean sources of water.
Travelers and athletes participating in water sports, such as those who compete in
triathlons, represent a growing population at risk. In the UK, ask for a history of rowing,
fishing, contact with animals or travel. The red discoloration of the eye seen initially is
subconjunctival haemorrhage which occurs in more than 90% of patients with
leptospirosis. Aminotransferase levels are usually elevated but they are rarely higher
than 200 U/L just as seen in this stem.
The single most appropriate investigation in this scenarior would be blood and urine
