Infectious Diseases Questions

Infectious Diseases

Infectious diseases, also known as transmissible diseases or communicable diseases, are illnesses caused by the spread of pathogenic microorganisms, such as bacteria, viruses, fungi, or parasites, from one person to another. These diseases can be spread through various modes of transmission, such as through the air, water, food, sexual contact, or contact with contaminated surfaces.

As a medical student, it is crucial to have a strong understanding of infectious diseases, as they play a significant role in public health and clinical medicine. By studying infectious diseases, you will learn how to recognize, diagnose, and treat these conditions, as well as how to implement preventive measures to reduce their spread.

To help reinforce your knowledge in this area, take the following multiple choice questions. You can identify any areas where you may need to improve your understanding. So, let’s get started!

Oesophageal candidiasis

A 32 year old male presents with weight loss over 6 months and swallowing difficult. He has an OGD which suggests oesophageal candidiasis is the most likely culprit. Which of the following is most likely to be true?

  • He is likely to have Ig A deficiency
  • He has HIV
  • He has AIDS
  • He has TB
  • He has recently been given a broad spectrum antibiotic

He has AIDS

Oesophageal candidiasis is not normal and an explainination needs to be found: immunosupression of some sort.

Oesophageal candidiasis suggests he is immunosupressed. With the weight loss, this makes the diagnosis of HIV the most likely.

You can get vaginal/oral candidiasis after antioibotics, but oesophageal suggest siginificant immunosupression.


Oesophageal candidiasis is an AIDS defining illness: along with…



PCP (Pneumocystis carinii pneumonia)

Blurred vision diagnosis

A 27 year old presents with blurred vision on generelised weakness.

The A&E doctor tells you on the telephone he suspects the patient “just wants a bed for the night”.

He gives a 12 hour histroty of symptoms.

In addition to this he also complains of

  • a chronic cough
  • an infected groin injection site
  • blurred vision
  • slurring of his speach

On your assessment he is not febrile.
He has a 3/5 weakness in both lowe limbs.
There is no sensory involvement.

He has some problems with his ocular movemements on cranial nerve examination, with a suggestion of a left 6th nerve palsy.

What is the most likely diagnosis?

  • Botulism
  • HIV infection
  • Tuberculosis Infection
  • Guillain Barre Syndrome
  • Tetanus
  • Malingering


The differential of botulism includes myasthenia, Organophosphate poisoning, stroke and any acute polyneuropathy.

Clostridium botulinim is an anaerobic bacterium which makes heat resistant spores that require temperatures >100oC to kill.

Tinned foods (dented tins) are often to blame…

The question is continued in the next stem.

HIV:: wouldn’t give you a specific weakness.
GBS wouldnt give you the ocular palsies (Miller Fisher syndome can). Often patients have sensory symptoms but no sensory sign.
Tetanus:: think trismus and spasticity (lockjaw etc) as a result of tetonaplasmin:: a toxoid that blocks acetylcholine release in the CNS.

Follow on inspection

He has some problems with his ocular movemements on cranial nerve examination, with a suggestion of a left 6th nerve palsy.

What is the most likely source of the botulism?

  • Skin/ Soft tissue
  • Respiratory
  • Diet / GI tract
  • genitourinary system
  • None of the answers listed here

Skin / Soft tissue

Classic: IVDU’s get botulism wound infections and then get the full blown symptoms. Other sources: food (esp tinned).


A 34 year Type I diabetic presents with what appears to be cellulitis over his left calf.

Temp 386
Sats 99% air
BM 26 mmol/l
Urinalysis 3+ blood only

Select the 2 commonest organisms which cause cellulitis in this case from the list below.

  • Neisseria
  • Clostridium
  • Haemophilus
  • Staphlococcus Aureus
  • Mycobacterium
  • Streptococcus Pyogenes
  • Enterococcus
  • Candida

Streptococcus Pyogenes and Staphlococcus Aureus

Staph and step are the commonest mycobacterium.


What is the most appropriate treatment for the patient above?

  • Treat as infection and diabetic ketoacidosis
  • Oral antibiotics with community follow up
  • Intravenous antibiotics with other supportive care
  • Intravenous antibiotics and treat as diabetic ketoacidosis
  • referral to orthopaedic surgeons for opinion regarding debridement

Treat as infection and diabetic ketoacidosis, Oral antibiotics with community follow up

Uncomplicated cellulitis can be treated initially with oral antibiotics, commonly flucloxacillin 500mg QDS (check if penicillin allergic, exams).

However cases complicated by systemic illness (e.g. fever), diabetics etc may ned hospital admission and administration of IV antibiotics.

e.g. Flucloxacillin 2g QDS IV.

Red lumps on shins

A man presents with painful red lumps on the front of his shins. Without taking any history which of the following is the most likely diagnosis?

  • Syphillis
  • Brucellosis
  • Hepatitis C
  • Lyme disease
  • Streptococcal infection

Streptococcal infection

Clinical pearl:

Causes of erythema nodosum (the painful reddish lumps on the front of shins).

Infectious: TB, Streptococcal infection, leprosy, Strep.

Drugs: Sulphonamides, Dapsone & a load more.

IBD: Crohns & UC.

Rare: BCG inoculation.

Misc: HIV, Sarcoid.

Lyme disease causes (deep breath) rash (erythema chonicum migrans)/arthralgia/heart block/ cranial nerve palsies. You need to be bitten by the tick (Borriela Burgdorferi) and that means you should have been somewhere like the new forest!

Non blanching purpuric rash

A 26 year old male presents with a non blanching purpuric rash on his feet for the last 72 hours. He is otherwise well in himself and has spent the morning at work. His clinical examination (CVS RESP GIT GU) is otherwise normal. Urinalysis is positive for protien 1+.From the following which is the most likely diagnosis?

  • Wegener’s Granulomatosis
  • Meningococcal septicaemia
  • Henoch Schonlein purpura
  • Sarcoid
  • Bacterial Meningitis

Henoch Schonlein purpura

HSP is a common presentation of a non blanching rash that can be clinically indistinguishable from that of meningcococcal septicaemia.

So go to the history

26years old: Any of the above

72 hours of symptoms: this makes a bacterial meningitis unlikely as it does meningococcal septicaemia (but not impossible)

What about Wegeners: that can present with a vasculiti rash… but: its very rare, and presents generally with respiratory symptoms (haemopysis/cough/s.o.b.), nasal symptoms (crusting/bleeding nose), and renal involvement (Glomerulonephritis: blood and protein on urine dipstic)

Therefor the diagnosis is most likely HSP: an a sometimes self limiting autoimmune illness (can also have GIT/Renal/ Musculoskeletal involvement). The rash often involves only the buttocks/ lower limbs.

Obstructive vs Hepatitis

Hepatits tests

A patient presents with the following results following an episode of jaundice. They show the following

Hb 14.6 g/dl

Albuming 42

Alk Phos 140 (<110)

ALT 540 (<40)

Bilirubin 51

INR 1.4

Which of the following is true

  • It is an “obstructive picture” of LFT’s
  • It’s a “hepatitic” picture* of LFT’s

It’s a “hepatitic” picture* of LFT’s

Hepatitic: significant rise in ALT without so much a rise in the “cholestatic” enzymes alkaline phosphatase or bilirubin (also excreted in the bile).

I.e. very high ALT with slightly high Alk Phos / bilirubin = hepatitic.

Suspected bells palsy

A 37 year old intra venous drug user is referred by his GP a suspected bells palsy. On examining his inner ear there are a number of vesicles visible on his ear drum. His cranial nerve examination reveals an Lower motor neurone facial nerve palsy. The most likely diagnosis is:

  • Steven Johnson Syndrome
  • Ramsay Hunt Syndrome
  • HIV
  • Stroke
  • Bells Palsy

Ramsay Hunt Syndrome

Bells is a lower motor neurone neurone lesion which is idiopathic in nature.

The aetiology is probably thought to be a herpes virus and there is some evidence to support the use of short course oral corticosteroids and acyclovir.

However:: Ramsay Hunt is a facial nerve palsy with associated herpes zoster infection (as manifested in this case by the vesicles).

Follow on question

Why may the patient have tinnitus?

  • Involvement of CN5
  • Involvement of CN6
  • Involvement of CN7
  • Involvement of CN8
  • Involvement of CN9

Involvement of CN8
The vestibulocochlear/auditory nerve (CN8) lies in close proximity to the geniculate ganglion and the facial nerve. Hence the varicella zoster can affect this branch also causing tinnitus and vertigo.


Which of the following is incorrect about patients infected with tuberculosis for >1 year.

  • Patients can completely asymptomatic
  • Pateints can have erythema nodosum
  • Patients can have hilar lymphadenopathy
  • Respiratory involvement characteristically involves the mid zones
  • TB can present with no respiratory involvement

Respiratory involvement characteristically involves the mid zones

Clinical pearl!

Only a few things primarily affect the apex of the lungs causing apical fibrosis. The Acronym is TEARS:


Extrinsic Allergic Alveolitis

Ankylosing Spondylitis



If you see this on an examination paper always think of one of the above diagnoses. Its an easy question to write for examiners.

UMN lesion

Continued from previous stem. [A 24 year old woman presents with a 2 day history of unilateral left sided facial weakness of the lower part of her face. She is able to frown and raise her eyelids. Otoscopy is normal. Clinical examination is otherwise normal. Routine blood tests are normal. She is clinically improving.]

The problem/defect/lesion is likely to be…

  • In the right cerebral hemisphere
  • In the left cerebral hemisphere
  • In the trigeminal nerve on the left side
  • In the facial nerve on the right side
  • In the facial nerve on the left side

In the right cerebral hemisphere

Its an UMN lesion and therefore the site is in the contralateral side of the brain! Facial nerves do innervate ipsilaterally, so a right sided LMN facial nerve weakness would cause weakness of the right side of the face.


Right sided middle cerebral artery infarct would cause a left sided facial weakness (UMN) and the upper half of the forehead would be spared:: bilateral innervation.

Right sided CNVII Palsy would cause a right sided facial weakness.

Unilateral left sided facial weakness

A 24 year old woman presents with a 2 day history of unilateral left sided facial weakness of the lower part of her face. She is able to frown and raise her eyelids. Otoscopy is normal. Clinical examination is otherwise normal. Routine blood tests are normal. She is clinically improving. What is your advice?

  • She needs investigation for causes of a mononeuropathy (sarcoid/lyme/diabetes etc)
  • She is likely to have guillain barre syndrome and therefore needs admission
  • She needs admission for further investigation
  • Bells palsy: no inpatient treatment required but consider steroid/aciclovir

She needs admission for further investigation

Think this does not look like a Bells palsy (ideopathic LMN CNVII lesion).

Virus for chickenpox

Which infection is the cause of “chickenpox” and ”shingles”?

  • Herpes Simplex virus
  • Human herpes virus 8
  • Herpes Zoster Virus
  • There are separate viruses for “chickenpox” and “shingles”
  • None of the Listed answers are correct

Herpes Zoster Virus

Herpes Zoster is the virus that causes ‘varicella zoster’ or ‘shingles’. It characteristically causes a vesicular rash with vesicles at different stages of development. Herpes simplex is responsible for genital herpes/ most encephalitis caused by herpes virus.