infection PT 1 2016 modif

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Question 1 of 153

At what CD4 count should highly active anti-retroviral treatment (HAART) commence in
asymptomatic HIV patients?
A

Below 600/mm3

B

Below 400/mm3

C

Below 350/mm3

D

Below 100/mm3

E

Below 50/mm3

Explanation

Timing of treatment in human immunodeficiency virus infection
A number of cohorts exist, providing important data on the natural history and
progression of HIV infection
Multiple logistic regression can and has been used to determine the optimal point at
which to start HAART, and it appears that the point where the benefit of HAART
outweighs the risk is around 350 mm3
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Question 2 of 153

A 22-year-old woman returns from a holiday on the Kenyan coast. She develops a fever,
deteriorates over the next 48 h and becomes unconscious and unrousable. She has acute
renal failure. Which one of the following options is the most appropriate investigation?
A

Computed tomography (CT) scan, head

B

Electroencephalograph (EEG)

C

Erythrocyte sedimentation rate (ESR)

D

Repeated thick and thin blood smear

E

C-reactive protein (CRP)

Explanation
Complications in malaria treatment
The patient in the present case has extremely severe falciparum malaria, with cerebral
malaria (coma) and renal failure (usually pre-renal) needing renal replacement therapy
Patients with full-blown cerebral malaria are at an increased risk of fitting, which may
be treated with diazepam
Administration of prophylactic anticonvulsants may be associated with an increased

mortality
Exchange transfusion is recommended for a parasitaemia > 10% with complications (or
> 30% if no other complications)
Treatment of the malaria is with IV quinine, which increases insulin secretion and the
sensitivity of cells to insulin and can cause hypoglycaemia
Malaria itself can cause hypoglycaemia too, so blood glucose should be monitored
every 2 h
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Question 3 of 153

Which one of the following organisms is the most frequent cause of hospital-acquired
infections and is also developing increasing resistance to antimicrobial agents?
A

Staphylococcus aureus

B

Streptococcus pneumoniae

C

Toxoplasma gondii

D

Pneumocystis jirovecii (formerly called Pneumocystis carinii)

E

Listeria monocytogenes

Explanation
Staphylococcus aureus infection
Epidemiological studies of Staphylococcus aureus infection, and increasingly these
concern meticillin-resistant Staph. aureus (MRSA) strains, require typing methods to
distinguish between epidemic and endemic strains
Staph. aureus is part of the normal flora in some individuals; about 25% of people carry
the organism permanently, a similar proportion never do, and the rest do so

intermittently
Common carriage sites are the nose, axillae, perineum and toe webs
Nasal carriage rates vary from 10% to 40% in normal adults outside a hospital
environment, but higher rates are often found in hospital patients, particularly those
who have been in hospital for several weeks
High carriage rates are also found in those with skin diseases such as eczema, those
with insulin-dependent diabetes, patients on chronic haemodialysis or chronic
ambulatory peritoneal dialysis, intravenous drug users and human immunodeficiency
virus (HIV)-positive patients
Some carriers disperse large numbers of staphylococci into the environment on skin
squamae
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The carrier state is highly relevant to the epidemiology of Staph. aureus infection as to
whether or not this complicates surgery or trauma; the source of Staph. aureus in most
patients who develop a staphylococcal infection is endogenous
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Question 4 of 153

A 49-year-old woman is referred to you by her GP for suspected chronic fatigue syndrome.
Which one of the following features would suggest that this was an incorrect diagnosis?
A

Dysphagia

B

Frequent headaches

C

Memory impairment

D

Recurrent sore throats

E

Severe myalgia

Explanation
Chronic fatigue syndrome
A diagnosis of chronic fatigue syndrome (CFS) requires the presence of unexplained
chronic fatigue for more than six months
Although several formal definitions exist, cardinal features of CFS (besides fatigue)
include impaired memory or concentration, sore throats, myalgia, arthralgia, headaches,
unrefreshing sleep and post-exertion malaise
CFS is a diagnosis of exclusion, which requires the absence of any other underlying
organic or psychiatric problem
Dysphagia
Dysphagia might reflect an underlying oesophageal cancer, and should be investigated
urgently
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Question 5 of 153

A 25-year-old soldier presents to the Emergency Department with a high fever, diarrhoea and
vomiting. He returned from his recent posting to rural Sierra Leone 10 days ago and has
become unwell over the last 24 h. On admission he looks unwell and has a temperature of 39
°C. He has a pulse rate of 110 bpm. Examination is otherwise unremarkable. Which one of the
following options is the most appropriate next step?
A

Send samples for FBC, clotting, U&Es, LFTs and a malaria film to the lab

B

Send the patient direct to an isolation unit

C

Send samples for a malaria film to the lab

D

Send samples for FBC, clotting, U&Es, LFTs, a malaria film and blood cultures to the
lab

E

Send the patient home

Explanation
Malaria/Viral Haemorrhagic Fever Differential
The most likely diagnosis in the present case is malaria, in the current climate however
the major concern is for viral haemorrhagic fever, in particular a differential of Ebola,
and as such guidance has changed from that previously recommended
In the past, in someone returning from rural Sierra Leone guidance was send only one
sample for malaria (if positive for malaria, can relax and treat for malaria)
New guidance dictates that if suspicion of viral haemorrhagic fever, then don't even
take a single sample to avoid exposure risk for lab staff, send directly to an isolation
unit (Royal Free, Newcastle, Liverpool, Sheffield) - so this would encompass anyone
returning from rural West Africa and with a differential of viral haemorrhagic fever and
within the 21 day maximum incubation period
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Question 6 of 153

A 12-year-old boy has had a gradually progressive plaque on his buttock for the past 3 years.
The plaque is 15 cm in diameter, irregular in shape with crusting and induration at the
periphery and scarring at the centre. Which one of the following options is the most likely
diagnosis?
A

Tinea corporis

B

Granuloma annulare

C

Lupus vulgaris

D

Borderline leprosy

E

Cutaneous leishmaniasis

Explanation
Differential diagnosis of plaque-forming infections
Lupus vulgaris

An irregular plaque like lesion with central scarring is suggestive of lupus vulgaris
This is the commonest manifestation of cutaneous tuberculosis
Ringworm infection

Ringworm (Tinea corporis) infection usually presents with slightly itchy, asymmetrical
scaly patches that show central clearing and an advanced scaly raised edge
Occasionally vesicles or pustules may be seen in the edge
Granuloma annulare

This is a dermatosis predominantly of children and young adults
It is characterised by clusters of small dermal papules that often form into rings or part
of a ring
As they heal, the centre becomes dusky and altered in texture
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Borderline leprosy (BB)

This presents with numerous skin lesions that may form macules, papules and plaques
The annular-rimmed lesion with a punched-out hypopigmented anaesthetic centre is

characteristic
There is widespread nerve involvement and limb deformity
Cutaneous leishmaniasis

This presents as a single or multiple painless nodules that enlarge and ulcerate with a
characteristic erythematous raised border
An overlying crust may develop
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Question 7 of 153

A 24-year-old asylum seeker from Zimbabwe is currently on anti-tuberculous therapy with
rifampicin and isoniazid for pulmonary tuberculosis. He is HIV-seropositive with a CD4 count
of 300 cells/μl and 2 weeks ago he was commenced on high active anti-retroviral therapy
with zidovudine, lamivudine and nevirapine. He presents with a widespread maculopapular
rash. Which one of the following options is the most likely cause of the rash?
A

Rifampicin

B

Immune reconstitution disease

C

Kaposi’s sarcoma

D

Non-nucleoside reverse-transcriptase inhibitors

E

Nucleoside reverse-transcriptase inhibitors

Explanation
Rashes in anti-retroviral therapy
Maculopapular rash an important and frequently encountered problem in anti-retroviral
therapy
Nevirapine is a non-nucleoside reverse-transcriptase inhibitor, a class of drugs well
recognised to cause maculopapular rashes This is the rationale for starting low-dose
therapy with nevirapine in the first 2 weeks
Zidovudine and lamivudine are nucleoside reverse-transcriptase inhibitors, which are
less frequently associated with rashes
Further investigations

In addition to the temporal clues, the presence of an eosinophilia should be sought, a

finding seen in drug-associated rashes
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Question 8 of 153

A 21-year-old student taking the contraceptive pill develops pain and soreness around the
genitals. She has just completed an elective year in the USA. On examination there are
multiple, shallow and tender ulcers at the skin and mucous membrane of the vagina. The
most probable diagnosis is:
A

Genital herpes

B

Chancroid

C

Granuloma inguinale

D

Primary syphilis

E

Lymphogranuloma venereum

Explanation
Genital herpes
Underlying causes

Infectious aetiologies of genital ulcers include herpes simplex virus (HSV), chancroid
(Haemophilus ducreyi), granuloma inguinale (Calymmatobacterium granulomatis),
syphilis (Treponema pallidum), HIV-specific ulcers (acute HIV infection or late HIV), and
lymphogranuloma venereum (LGV, Chlamydia trachomatis serovars L1–3)
Non-infectious aetiologies include fixed drug reactions, Behçet’s disease, neoplasms,
and trauma
It is particularly important to consider these alternative causes if evaluations for the

infectious aetiologies do not lead to a diagnosis
HIV infection should always be considered and tested for
Epidemiology

Genital ulcers occur in sexually active individuals throughout the world
The relative frequency of each of the infectious aetiologies differs depending on
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geographic location
The most common causes of genital ulcers in sexually active young adults in the USA
are herpes simplex virus (HSV), syphilis, and chancroid
Of these three infections, ulcers due to HSV are the most prevalent, followed by
primary syphilis and then chancroid
Infection with each of these organisms is not mutually exclusive, and coinfection with
multiple organisms occurs
Clinical presentation

Genital ulcers caused by HSV are frequently multiple, shallow and tender, while
chancroid often presents with deep, undermined and purulent ulcers
When a painless, indurated, clean-based ulcer is present, the diagnosis of syphilis is
more likely
Laboratory investigations

A number of laboratory tests can be used to make an accurate diagnosis:

Gram stain and culture on selective media (for H. ducreyi)
Tzanck preparation, direct fluorescence antibody (DFA), and viral culture (for
HSV)
serological tests (for syphilis and LGV)
darkfield microscopy (for syphilis)
tissue biopsy (syphilis, granuloma inguinale)
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Question 9 of 153

A backpacker who has recently returned from Indonesia is diagnosed as having as a nocardial
infection. What would be the best technique for isolating and culturing the organism?

A

Paraffin bait

B

Cell culture

C

Anaerobic culture

D

Blood culture

E

Footpads of mice

Explanation
Culture techniques for pathogenic organisms
Nocardia spp use paraffin as a source of carbon for growth
In this technique, a paraffin wax-coated glass rod is placed in the inoculated
carbon-free broth
Nocardia grow on the rod at the air–liquid interface
They are relatively slow to grow in blood cultures
Footpads of mice are used to grow of Mycobacterium leprae
Cell culture techniques are used to isolate Chlamydia trachomatis
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Question 10 of 153

A 42-year-old single man who has been living in Thailand returns to the UK for a medical
consultation as he has deteriorating health. He admits to engaging in casual sexual
relationships during his time in the country. Over the past few weeks he has begun suffering
increasing night sweats, weight loss and diarrhoea. On examination his BP is 105/65 mmHg,
pulse is 85/min and regular. There is peripheral lymphadenopathy and right upper quadrant
pain on abdominal examination. His BMI is 21.

Investigations;
Hb

9.1 g/dl

WCC

5.1 x109/l

PLT

181 x109/l

Na+

137 mmol/l

K+

4.9 mmol/l

Creatinine

138 micromol/l

ALT

249 U/l

Stool culture and microscopy

negative for cysts and ovae

Which of the following is the most likely diagnosis?
Your answer was incorrect

A

Blastomycosis

B

Cryptosporidium

C

Cytomegalovirus

D

Histoplasmosis

E

Mycobacterium avium complex

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Explanation
The answer is Mycobacterium avium complex (MAC) The implication of this man’s gradually deteriorating health during his stay in Thailand is that
he has developed AIDS and the GI upset seen here is related to MAC. Serological testing to
confirm the diagnosis of MAC is under development, currently culture of AAFB is required to
confirm its presence. This patient should of course also have an HIV test. Typically patients
are treated with combination antimicrobials, (a macrolide, Ethambutol and Rifampicin).
Blastomycosis is manifest by predominant respiratory symptoms, as is histoplasmosis.
Cryptosporidium is diagnosed by the presence of oocysts on stool culture, and CMV is
associated with a more acute presentation than that seen here.
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Question 11 of 153

A patient presents with diarrhoea and vomiting. He is jaundiced. Hepatitis A infection is

diagnosed. Which one of the following modes of transmission is most likely?
A

Blood transfusion

B

Contaminated food

C

Ticks

D

Sexually

E

Mosquitoes

Explanation
Hepatitis A infection
Hepatitis A virus causes a self-limiting hepatitis
This RNA virus is acquired orally
The incubation period is between 2 and 6 weeks
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Question 12 of 153

A 32-year-old man from Uganda is referred to hospital with a high eosinophil count by his GP
following routine blood tests. He is entirely asymptomatic and has no past medical history of
note. Which of the following organisms is LEAST likely to be responsible?
A

Strongyloides stercoralis

B

Wuchereria bancrofti

C

Schistosoma mansoni

D

Schistosoma haematobium

E

Entamoeba histolytica

Explanation
Eosinophilia
Aetiology

Eosinophilia is associated with tissue-invasive helminths: strongyloidiasis, Wucheria
infection, schistosomiasis could all present in this way and should be screened for here
Other notes

Entamoeba histolytica is associated with a spectrum of illness, including colitis, liver
abscess, extra-gastrointestinal disease (central nervous system (CNS), pulmonary
involvement) and asymptomatic infection. Leukocytosis may occur but eosinophilia is
NOT a feature
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