Infectious Disease

Question 1

Urinary tract infections

Answer 1

Lower urinary tract infections (UTIs) involve infection in the bladder, causing cystitis (inflammation of the bladder).

Pyelonephritis refers to inflammation of the kidney resulting from bacterial infection. The inflammation affects the kidney tissue (parenchyma) and the renal pelvis (where the ureter joins the kidney).

Urinary tract infections are far more common in women, where the urethra is much shorter, making it easier for bacteria to get into the bladder.

The primary source of bacteria for urinary tract infections is faeces. Normal intestinal bacteria, such as E. coli, can easily journey to the urethral opening from the anus. Sexual activity is a crucial method for spreading bacteria around the perineum. Incontinence or poor hygiene can also contribute to the development of UTIs.

Urinary catheters are a possible source of infection, and catheter-associated urinary tract infections tend to be more serious and challenging to treat.

Question 2

Presentation of UTIs

Answer 2

Lower urinary tract infections present with:

Dysuria (pain, stinging or burning when passing urine)
Suprapubic pain or discomfort
Frequency
Urgency
Incontinence
Haematuria
Cloudy or foul-smelling urine
Confusion is commonly the only symptom in older and frail patients

Pyelonephritis has a similar presentation to lower urinary tract infections plus the additional triad of symptoms:

Fever
Loin or back pain (bilateral or unilateral)
Nausea or vomiting

Patients with pyelonephritis may also have:

Systemic illness
Loss of appetite
Haematuria
Renal angle tenderness on examination

TOM TIP: It is essential to distinguish between lower urinary tract infections and pyelonephritis. Pyelonephritis is a more severe condition with significant complications, including sepsis and kidney scarring. Suspect pyelonephritis in patients with:

Fever
Loin or back pain
Nausea or vomiting
Renal angle tenderness on examination

Question 3

Urine dipstick

Answer 3

Nitrites on a dipstick test suggest bacteria in the urine. Gram-negative bacteria (e.g., E. coli) break down nitrates (a normal waste product in urine) into nitrites.

Leukocytes are white blood cells. It is normal to have a small number of leukocytes in the urine, but a significant rise can result from an infection or other cause of inflammation. Leukocyte esterase (a product of leukocytes) is tested on a urine dipstick, indicating the number of leukocytes in the urine.

Red blood cells in the urine indicate bleeding. Microscopic haematuria is where blood is seen on a urine dipstick but not seen when looking at the sample. Macroscopic haematuria is where blood is visible in the urine. Haematuria is a common sign of infection but can also be present with other causes, such as bladder cancer or nephritis.

Nitrites are a better indication of infection than leukocytes. The NICE clinical knowledge summaries (June 2023) suggest that nitrites or leukocytes plus red blood cells indicate that the patient will likely have a UTI. The dipstick result is less reliable in catheterised patients or women over 65.

Where only nitrites are present, it is worth treating as a UTI. Where only leukocytes are present, a sample should be sent to the lab for further testing. Antibiotics may be considered where there is clinical evidence of a UTI.

A midstream urine (MSU) sample sent for microscopy, culture and sensitivity testing will determine the infective organism and the antibiotics that will be effective in treatment. Not all patients with an uncomplicated UTI require an MSU. An MSU is important in:

Pregnant patients
Patients with recurrent UTIs
Atypical symptoms
When symptoms do not improve with antibiotics

Question 4

Causes of UTIs

Answer 4

The most common cause of UTI is Escherichia coli, which are gram-negative, anaerobic, rod-shaped bacteria. They are part of the lower intestinal microbiome and can easily spread from faeces to the bladder.

Other causes:

Klebsiella pneumoniae (gram-negative, anaerobic, rod-shaped bacteria)
Enterococcus
Pseudomonas aeruginosa
Staphylococcus saprophyticus
Candida albicans (fungal)

Question 5

Managing lower UTIs

Answer 5

Follow local guidelines. An appropriate initial antibiotic in the community would be:

Nitrofurantoin (avoided in patients with an eGFR <45)
Trimethoprim (often associated with high rates of bacterial resistance)

Alternatives:

Pivmecillinam
Amoxicillin
Cefalexin

The typical duration of antibiotics is:

3 days of antibiotics for simple lower urinary tract infections in women
5-10 days of antibiotics for immunosuppressed women, abnormal anatomy or impaired kidney function
7 days of antibiotics for men, pregnant women or catheter-related UTIs

It is worth noting that NICE recommend changing the catheter when someone is diagnosed with a catheter-related urinary tract infection.

Question 6

Managing pyelonephritis

Answer 6

Referral to hospital is required if there are features of sepsis or if it is unsafe to manage them in the community.

NICE guidelines (2018) recommend the following first-line antibiotics for 7-10 days when treating pyelonephritis in the community:

Cefalexin
Co-amoxiclav (if culture results are available)
Trimethoprim (if culture results are available)
Ciprofloxacin (keep tendon damage and lower seizure threshold in mind)

Patients admitted to hospital with sepsis require the sepsis six, which includes a serum lactate, blood cultures, urine output monitoring, oxygen, empirical broad-spectrum antibiotics and IV fluids.

Two things to keep in mind with patients that have significant symptoms or do not respond well to treatment are:

Renal abscess
Kidney stone obstructing the ureter, causing pyelonephritis

Question 7

Pregnancy and UTIs

Answer 7

Urinary tract infections in pregnancy increase the risk of pyelonephritis, premature rupture of membranes and pre-term labour.

Question 8

Managing UTIs in pregnancy

Answer 8

Urinary tract infection in pregnancy requires 7 days of antibiotics. All women should have an MSU for microscopy, culture and sensitivity testing.

The antibiotic options are:

Nitrofurantoin (avoided in the third trimester)
Amoxicillin (only after sensitivities are known)
Cefalexin (the typical choice)

Nitrofurantoin should be avoided in the third trimester as there is a risk of neonatal haemolysis (destruction of the neonatal red blood cells).

Trimethoprim should be avoided in the first trimester as it works as a folate antagonist. Folate is essential in early pregnancy for the normal development of the fetus. Trimethoprim in early pregnancy can cause congenital malformations, particularly neural tube defects (e.g., spina bifida). It is not known to be harmful later in pregnancy but is generally avoided unless necessary.

Question 9

Cellulitis

Answer 9

Cellulitis is an infection of the skin and the soft tissues underneath. The skin forms a physical barrier between the environment and soft tissues. When a patient presents with cellulitis, look for a breach in the skin barrier and a point of entry for the bacteria. This may be due to skin trauma, eczema, fungal nail infections or ulcers.

Question 10

Presentation of cellulitis

Answer 10

Skin changes in cellulitis include:

Erythema (red discolouration)
Warm or hot to touch
Tense
Thickened
Oedematous
Bullae (fluid-filled blisters)
A golden-yellow crust indicates a Staphylococcus aureus infection

Patients may be systemically unwell, including having sepsis.

Question 11

Causes of cellulitis

Answer 11

The most common causes are:

Staphylococcus aureus
Group A streptococcus (mainly streptococcus pyogenes)
Group C streptococcus (mainly streptococcus dysgalactiae)

MRSA should be considered, particularly in patients the repeated hospital admissions and antibiotics.

Question 12

Severity of cellulitis

Answer 12

The Eron classification assesses the severity of cellulitis:

Class 1 – no systemic toxicity or comorbidity
Class 2 – systemic toxicity or comorbidity
Class 3 – significant systemic toxicity or significant comorbidity
Class 4 – sepsis or life-threatening infection

Question 13

Managing cellulitis

Answer 13

Class 3 and 4 cellulitis requires admission for intravenous antibiotics. Admission is also considered for frail, very young or immunocompromised patients and those with facial, periorbital or orbital cellulitis.

Flucloxacillin is the usual first-line antibiotic for cellulitis, either oral or intravenous. It is particularly effective against Staphylococcus aureus and also works well against other gram-positive cocci.

Alternatives:

Clarithromycin
Clindamycin
Co-amoxiclav (the usual first choice for cellulitis near the eyes or nose)

Question 14

Bacteria and ENT infections

Answer 14

Bacterial tonsillitis is most commonly caused by group A streptococcus (GAS) infections, mainly streptococcus pyogenes.

Otitis media, sinusitis and tonsillitis not caused by GAS are most commonly caused by:

Streptococcus pneumoniae

Other causes of otitis media, sinusitis and tonsillitis:

Haemophilus influenzae
Moraxella catarrhalis
Staphylococcus aureus

Question 15

Tonsillitis

Answer 15

The Centor criteria can be used to estimate the probability that tonsillitis is due to bacterial infection and will benefit from antibiotics. A score of 3 or more gives a 40 – 60 % probability of bacterial tonsillitis, and it is appropriate to offer antibiotics. A point is given if each of the following features are present:

Fever over 38ºC
Tonsillar exudates
Absence of cough
Tender anterior cervical lymph nodes (lymphadenopathy)

The FeverPAIN score is an alternative to the Centor criteria. A score of 2 – 3 gives a 34 – 40% probability, and 4 – 5 gives a 62 – 65% probability of bacterial tonsillitis:

Fever during the previous 24 hours
P – Purulence (pus on tonsils)
A – Attended within 3 days of the onset of symptoms
I – Inflamed tonsils (severely inflamed)
N – No cough or coryza

Question 16

Treating tonsillitis

Answer 16

Penicillin V (phenoxymethylpenicillin) for a 10-day course is typically first-line. It has a relatively narrow spectrum of activity and is effective against Streptococcus pyogenes.

Clarithromycin is the usual first-line choice in true penicillin allergy.

Question 17

Complications of tonsillitis

Answer 17

Peritonsillar abscess, also known as quinsy
Otitis media, if the infection spreads to the inner ear
Scarlet fever
Rheumatic fever
Post-streptococcal glomerulonephritis
Post-streptococcal reactive arthritis

Question 18

Otitis Media

Answer 18

Otitis media presents with reduced hearing and pain in the affected ear. Otoscopy will reveal a bulging red tympanic membrane. A perforated tympanic membrane can result in discharge from the ear.

Otitis media usually resolves within 3 to 7 days without antibiotics. Systemically unwell may need admission.

Question 19

Treating Otitis Media

Answer 19

The NICE clinical knowledge summaries (updated May 2023) suggest:

Amoxicillin for 5-7 days first-line
Clarithromycin (if penicillin allergic)
Erythromycin (in pregnant women allergic to penicillin)

Co-amoxiclav is a second-line option if the infection is not responding to amoxicillin.

Question 20

Sinusitis

Answer 20

Sinusitis is usually viral. Only around 2% of acute sinusitis is bacterial. Sinusitis typically last 2-3 weeks and resolves without treatment.

Question 21

Treating Sinusitis

Answer 21

NICE CKS (May 2023) recommend for patients with symptoms that are not improving after 10 days, the options of:

High-dose steroid nasal spray for 14 days (e.g., mometasone 200 mcg twice daily)
A backup antibiotic prescription, used if worsening or not improving within 7 days (phenoxymethylpenicillin first-line)

The options for chronic sinusitis (lasting more than 12 weeks) are:

Saline nasal irrigation
Steroid nasal sprays or drops (e.g., mometasone or fluticasone)
Functional endoscopic sinus surgery (FESS)

Question 22

Intra-abdominal infections

Answer 22

Acute diverticulitis (infection in intestinal diverticula)
Acute cholecystitis (with secondary infection in the gallbladder)
Ascending cholangitis (infection in the bile ducts)
Appendicitis (infection in the appendix)
Spontaneous bacterial peritonitis (infection in the fluid in the peritoneal cavity)
Intra-abdominal abscess

Question 23

Bacterial causes of intra-abdominal infections

Answer 23

Anaerobes (e.g., Bacteroides and Clostridium)
E. coli (gram-negative)
Klebsiella (gram-negative)
Enterococcus (gram-positive)
Streptococcus (gram-positive)

Question 24

Antibiotics and intra-abdominal infections

Answer 24

Intra-abdominal infections require broad-spectrum antibiotics until culture results are available. Antibiotics need to cover gram-positive, gram-negative and anaerobic bacteria.

Co-amoxiclav provides good gram-positive, gram-negative and anaerobe cover. It does not cover pseudomonas or atypical bacteria.

Quinolones (e.g., ciprofloxacin and levofloxacin) provide gram-positive, gram-negative and atypical cover. However, they do not cover anaerobes, so they are usually paired with metronidazole for intra-abdominal infections.

Metronidazole provides excellent anaerobe cover but does not provide any cover against aerobic bacteria.

Gentamicin provides excellent gram-negative cover and some gram-positive cover (particularly against staph). It is bactericidal, killing bacteria rather than just slowing them down.

Vancomycin provides excellent gram-positive cover, including MRSA. It is often combined with gentamicin (for gram-negative cover) and metronidazole (for anaerobe cover) in patients with penicillin allergy.

Cephalosporins provide good broad-spectrum cover against gram-positive and gram-negative bacteria but are not very effective against anaerobes. They are often avoided due to the risk of Clostridium difficile (C. diff) infection.

Piperacillin with tazobactam (tazocin) and meropenem are powerful antibiotics that cover gram-positive, gram-negative and anaerobic bacteria. They do not cover atypical bacteria or MRSA. Tazocin does not cover ESBLs. They are usually reserved for very unwell patients and those not responding to other antibiotics.

Local antibiotic policies will determine the choice based on local resistance and infection control issues. Typical regimes for treating intra-abdominal infection are:

Question 25

Septic arthritis

Answer 25

Septic arthritis refers to an infection in a joint. Infection in a joint is a medical emergency. The infection can rapidly destroy the joint and cause systemic illness. Septic arthritis has a mortality of around 10%.

Infection may occur in a native joint (an original joint) or a prosthetic joint replacement. Infection in a prosthetic joint is a big problem and happens in around 1% of joint replacements. Extensive measures are taken to prevent it, such as perioperative prophylactic antibiotics. It is more likely to occur in revision surgery than in the initial joint replacement.

Question 26

Presentation of septic arthritis

Answer 26

Septic arthritis usually only affects a single joint, often a knee. It presents with a rapid onset of:

A hot, red, swollen and painful joint
Stiffness and reduced range of motion
Systemic symptoms, such as fever, lethargy and sepsis

Question 27

Bacterial causes of septic arthritis

Answer 27

Staphylococcus aureus is the most common causative organism.

Other bacteria:

Neisseria gonorrhoea (gonococcus) in sexually active individuals
Group A Streptococcus (most commonly Streptococcus pyogenes)
Haemophilus influenza
Escherichia coli (E. coli)

TOM TIP: In a young patient presenting with a single acutely swollen joint, consider gonococcal septic arthritis until proven otherwise. The gram stain reveals a gram-negative diplococcus. Urinary or genital symptoms should also make you think of reactive arthritis (once gonococcal septic arthritis is excluded).

Question 28

Differentials of septic arthritis

Answer 28

The key differential diagnoses of a single warm swollen joint are:

Gout (joint fluid shows urate crystals that are negatively birefringent of polarised light)
Pseudogout (joint fluid shows rod-shaped calcium pyrophosphate crystals that are positively birefringent)
Reactive arthritis (typically triggered by urethritis or gastroenteritis and associated with conjunctivitis)
Haemarthrosis (bleeding into the joint, usually after trauma)

Question 29

Managing septic arthritis

Answer 29

Have a low threshold for suspecting septic arthritis, particularly in immunosuppressed patients. Delayed treatment has significant consequences. Joint fluid examination is usually required to exclude septic arthritis.

There will be a local acute hot joint policy to guide what team admits the patient (e.g., orthopaedics, rheumatology or infectious diseases), what antibiotics to use and for how long.

Joint aspiration is performed before starting antibiotics. The sample is sent for gram staining, crystal microscopy, culture and antibiotic sensitivities. The joint fluid may be purulent (full of pus). The gram stain result is usually available quickly and may give a clue about the organism. Culture and antibiotic sensitivities take longer.

Empirical IV antibiotics should be given until the sensitivities are known. Antibiotics are usually continued for 4-6 weeks in total (initially IV, then oral). The choice of antibiotic depends on local guidelines. Example choices are:

Flucloxacillin (often first-line)
Clindamycin (penicillin allergy)
Vancomycin (if MRSA is suspected)

Ceftriaxone is typically used for treating Neisseria gonorrhoea.

Question 30

Influenza

Answer 30

The influenza virus is an RNA virus. Three types of influenza, A, B and C, affect humans (a D type affects cattle). A and B are the most common. Type A has different H and N subtypes. Examples of A strains are H1N1 (which caused the Spanish flu pandemic of 1918 and the swine flu pandemic of 2009) and H5N1 (which causes bird flu). Outbreaks of flu typically occur during the winter.

Question 31

Influenza and vaccination

Answer 31

Every year the influenza vaccine is altered to target multiple strains that are circulating that year. Yearly vaccines are required.

The flu vaccine is free on the NHS to people at higher risk of developing flu or flu-related complications:

Aged 65 and over
Young children
Pregnant women
Chronic health conditions, such as asthma, COPD, heart failure and diabetes
Healthcare workers and carers

Question 32

Presentation of Influenza

Answer 32

The delay between exposure and symptoms is usually around 2 days. Typical presenting features include:

Fever
Lethargy and fatigue
Anorexia (loss of appetite)
Muscle and joint aches
Headache
Dry cough
Sore throat
Coryzal symptoms

TOM TIP: There is a lot of overlap between the common cold and flu, but some key features can help you differentiate them clinically. Flu tends to have an abrupt onset, whereas a common cold has a more gradual onset. Fever is a typical feature of the flu but is rare with a common cold. Finally, people with the flu are “wiped out” with muscle aches and lethargy, whereas people with a cold can usually continue many activities.

Question 33

Testing and Influenza

Answer 33

Testing may be considered to confirm the diagnosis and monitor circulation and outbreaks. The UK Health Security Agency (UKHSA) monitors the number of flu cases and provides guidance when the numbers are high.

Point-of-care tests using swabs are available, giving a rapid result. They detect viral antigens. They are not as sensitive as formal lab tests and do not give information about the subtype of the virus.

Viral nasal or throat swabs can be sent to the local virology lab for polymerase chain reaction (PCR) analysis. This can confirm the diagnosis and help with tracking case numbers and patterns.

Question 34

Managing Influenza

Answer 34

Healthy patients who are not at risk of complications do not need treatment. The infection will resolve with self-care measures, such as adequate fluid intake and rest.

There are two options for treatment in someone at risk of complications of influenza:

Oral oseltamivir (twice daily for 5 days)
Inhaled zanamivir (twice daily for 5 days)

Treatment needs to be started within 48 hours of the onset of symptoms to be effective.

Post-exposure prophylaxis may be given where patients meet specific criteria:

It is started within 48 hours of close contact with influenza
Increased risk (e.g., chronic disease or immunosuppression)
Not protected by vaccination (e.g., it has been less than 14 days since they were vaccinated)

Options for post-exposure prophylaxis are:

Oral oseltamivir 75mg once daily for 10 days
Inhaled zanamivir 10mg once daily for 10 days

Question 35

Complications of Influenza

Answer 35

Otitis media, sinusitis and bronchitis
Viral pneumonia
Secondary bacteria pneumonia
Worsening chronic health conditions, such as COPD and heart failure
Febrile convulsions (young children)
Encephalitis

Question 36

Gastroenteritis

Answer 36

Acute gastritis is stomach inflammation and presents with epigastric discomfort, nausea and vomiting. Enteritis is inflammation of the intestines, and presents with abdominal pain and diarrhoea. Gastroenteritis is inflammation all the way from the stomach to the intestines and presents with pain, nausea, vomiting and diarrhoea.

The most common causes of gastroenteritis are viruses. Viral gastroenteritis is very easily spread, and patients often have an affected family member or contact. It is essential to isolate the patient in a healthcare environment, such as a hospital ward or assessment unit, as it can spread to other patients.

Most people recover well. However, gastroenteritis can rarely be fatal, especially in very young or old patients or those with other health conditions.

Question 37

Viral gastroenteritis

Answer 37

Viral gastroenteritis is common. It is highly contagious. Specific viruses include:

Rotavirus
Norovirus
Adenovirus (tends to cause respiratory symptoms)

Question 38

Escherichia Coli and Gastroenteritis

Answer 38

Escherichia coli (E. coli) is a normal intestinal bacteria. Only certain strains cause gastroenteritis. It is spread through contact with infected faeces, unwashed salads and contaminated water.

E. coli 0157 produces the Shiga toxin. The Shiga toxin causes abdominal cramps, bloody diarrhoea and vomiting. It also destroys blood cells, leading to haemolytic uraemic syndrome (HUS).

The use of antibiotics increases the risk of haemolytic uraemic syndrome. Therefore, antibiotics should be avoided if E. coli gastroenteritis is a possibility.

Question 39

Campylobacter Jejuni and Gastroenteritis

Answer 39

Campylobacter is a common cause of travellers’ diarrhoea. It is the most common bacterial cause of gastroenteritis worldwide. Campylobacter means “curved bacteria”. It is a gram-negative bacteria that is curved or spiral-shaped. It is spread by:

Raw or improperly cooked poultry
Untreated water
Unpasteurised milk

Incubation is usually 2 to 5 days. Symptoms resolve after 3 to 6 days. Symptoms are:

Abdominal cramps
Diarrhoea often with blood
Vomiting
Fever

Antibiotics can be considered after isolating the organism where patients have severe symptoms or other risk factors, such as HIV or heart failure. Clarithromycin is often first-line. Azithromycin and ciprofloxacin are alternative options.

Question 40

Shigella and Gastroenteritis

Answer 40

Shigella is spread via faeces, either person-to-person or through contaminated drinking water or food. The incubation period is 1-2 days, and symptoms usually resolve within one week. It causes bloody diarrhoea, abdominal cramps and fever. Shigella can produce the Shiga toxin, which can cause haemolytic uraemic syndrome. Treatment of severe cases is with azithromycin or ciprofloxacin.

Question 41

Salmonella and Gastroenteritis

Answer 41

Salmonella is spread by eating raw eggs or poultry or food contaminated with the infected faeces of small animals. The incubation period is 12 hours to 3 days, and symptoms usually resolve within one week. Symptoms are watery diarrhoea, which may be associated with mucus or blood, abdominal pain and vomiting. Antibiotics are only necessary in severe cases and are guided by stool culture and sensitivities (e.g., ciprofloxacin).

Question 42

Bacillus Cereus and Gastroenteritis

Answer 42

Bacillus cereus is a gram-positive rod spread through contaminated cooked food. It grows on food not immediately refrigerated after cooking (e.g., fried rice or cooked pasta left at room temperature).

Whilst growing on the food, it produces a toxin called cereulide that causes abdominal cramping and vomiting within 5 hours of ingestion. Reheating the food can kill the bacteria but does not destroy the cereulide toxin. When Bacillus cereus arrives in the intestines, it produces different toxins that cause watery diarrhoea. Diarrhoea occurs more than 8 hours after ingestion. All of the symptoms usually resolve within 24 hours.

The typical course is vomiting within 5 hours, diarrhoea after 8 hours and resolution within 24 hours.

TOM TIP: The typical exam patient with Bacillus cereus develops symptoms soon after eating fried rice that has been left at room temperature. They develop symptoms shortly afterwards, then recover within 24 hours. Examiners like this question because the course is easily distinguished from other causes of gastroenteritis.

You may also come across Bacillus cereus with infective endocarditis in intravenous drug users (IVDU), where heroin is contaminated. However, Staph aureus is the most common cause of infective endocarditis in IVDU.

Question 43

Yersinia Enterocolitica and Gastroenteritis

Answer 43

Yersinia enterocolitica is a gram-negative bacillus. Pigs are key carriers, and eating raw or undercooked pork can cause infection. It is also spread through contact with infected humans, animals or faeces.

Yersinia typically affects children, causing watery or bloody diarrhoea, abdominal pain and fever. Incubation is 4-7 days. It can last longer than other causes of enteritis, with symptoms lasting 3 weeks or more. Older children and adults can present with right-sided abdominal pain due to mesenteric lymphadenitis (inflammation in the intestinal lymph nodes) and fever, which can give the impression of appendicitis.

Antibiotics are only necessary in severe cases and are guided by stool culture and sensitivities.

Yersinia pestis (a different specie of Yersinia) is spread through rat flea bites and causes plague.

Question 44

Staphylococcal Enterotoxins and Gastroenteritis

Answer 44

Staphylococcus aureus can produce enterotoxins when growing on foods such as eggs, dairy and meat. When eaten, these toxins cause inflammation in the intestines, with symptoms of diarrhoea, vomiting, abdominal cramps and fever. These symptoms start within hours of ingestion and settle within 12 to 24 hours. It is the enterotoxin causing symptoms rather than the bacteria.

Question 45

Giardiasis and Gastroenteritis

Answer 45

Giardia lamblia is a type of microscopic parasite. It lives in the small intestines of mammals. These mammals may be pets, farmyard animals or humans. It releases cysts in the faeces. The cysts may contaminate food or water. When eaten, they infect a new host. This is called faecal-oral transmission.

Infection may not cause any symptoms, or it may cause chronic diarrhoea. Diagnosis is made by stool microscopy. Treatment is with tinidazole or metronidazole.

Question 46

General Principles of Management of Gastroenteritis

Answer 46

Food poisoning is a notifiable disease. The UK Health Security Agency (UKHSA) should be notified of suspected cases. When notifiable organisms (e.g., Giardia) are identified on testing, the lab must notify UKHSA.

Good hygiene helps prevent gastroenteritis. When patients develop symptoms, they should immediately be isolated in order to avoid spread. Barrier nursing and rigorous infection control are important for inpatients.

A faeces sample can be tested with microscopy, culture and sensitivities to establish the causative organism and antibiotic sensitivities.

Dehydration is the primary concern. The key to management is establishing whether patients can keep themselves hydrated or need admission for IV fluids. Antibiotics are generally not recommended or required. Most patients make a full recovery with simple, supportive management.

Oral rehydration salt solution (e.g., Dioralyte sachets mixed with water) can help replace losses in patients at increased risk of dehydration (e.g., frail patients). These contain glucose, potassium and sodium.

Antidiarrhoeal drugs (e.g., loperamide) and antiemetics (e.g., metoclopramide) are generally avoided, as they can worsen the condition. The NICE Clinical Knowledge Summaries (updated June 2023) suggest antidiarrhoeal drugs may be helpful in mild-moderate diarrhoea but should be avoided with E. coli 0157, shigella or bloody diarrhoea.

Antibiotics are only used in patients at risk of complications once the causative organism is confirmed.

Once the oral intake is better tolerated, a light diet with small quantities of bland foods can be introduced. Patients should stay off work or school for 48 hours after symptoms resolve entirely.

Question 47

Post-Gastroenteritis complications

Answer 47

Lactose intolerance
Irritable bowel syndrome
Reactive arthritis
Guillain–Barré syndrome
Haemolytic uraemic syndrome

Question 48

Clostridium Difficile

Answer 48

Clostridium difficile (“C. diff”) is a gram-positive, rod-shaped, anaerobic bacteria. Infection is associated with repeated use of antibiotics, proton-pump inhibitors (e.g., omeprazole) and healthcare settings.

C. difficile produces spores, which are released in faeces. The spores can survive on contaminated surfaces and hands, helping it spread to others.

It may colonise the intestines without causing any symptoms or issues. When antibiotics interrupt the normal intestinal microbiome, C. difficile can proliferate and get out of control. It can produce toxins, particularly toxin A (enterotoxin) and toxin B (cytotoxin), which cause symptoms and complications.

Question 49

Antibiotics associated with C. difficile

Answer 49

The antibiotics most associated with C. difficile start with the letter C:

Clindamycin
Ciprofloxacin (and other fluoroquinolones)
Cephalosporins
Carbapenems (e.g., meropenem)

Question 50

Presentation of C. difficile

Answer 50

Colonisation is usually asymptomatic.

Infection presents with diarrhoea, nausea and abdominal pain.

Severe infection with colitis can present with:

Dehydration
Systemic symptoms (e.g., fever, tachycardia and hypotension)

Question 51

Diagnosing C. difficile

Answer 51

Diagnosis is based on stool samples. Stools can be tested for:

C. difficile antigen (specifically glutamate dehydrogenase)
A and B toxins (by PCR or enzyme immunoassay)

The antigen test shows whether C. difficile is present but not whether it is producing toxins. The antigen is the initial screening test and is followed up with tests for toxins if C. difficile is identified.

Question 52

Managing C. difficile

Answer 52

Management is with supportive care and oral antibiotics. The options are:

Oral vancomycin (first-line)
Oral fidaxomicin (second-line)

Patients need to be isolated until 48 hours after the last episode of diarrhoea. There is a high recurrence rate.

Faecal microbiota transplantation is an option for recurrent cases. The stool microbiome from a donor is transferred to the patient via capsules, colonoscopy or enema.

Question 53

Complications of C. difficile

Answer 53

Pseudomembranous colitis is characterised by inflammation in the large intestine, with yellow/white plaques that form pseudomembranes on the inner surface of the bowel wall. It is seen during a colonoscopy and confirmed with biopsies to examine the histology.

Toxic megacolon is a complication of severe inflammation in the large intestine and involves dilation of the colon. Patients with toxic megacolon are very unwell and have a high risk of bowel rupture. Treatment involves supportive care and surgical resection of the affected bowel.

Additional complications include bowel perforation and sepsis.

Question 54

Meningitis

Answer 54

Meningitis is inflammation of the meninges, usually due to infection. The meninges are the lining of the brain and spinal cord. Cerebrospinal fluid (CSF) is contained within the meninges (in the subarachnoid space).

Question 55

Bacterial meningitis

Answer 55

The causes of bacterial meningitis include:

Neisseria meningitidis
Streptococcus pneumoniae (pneumococcus)
Haemophilus influenzae
Group B streptococcus (GBS) (particularly in neonates as GBS may colonise the vagina)
Listeria monocytogenes (particularly in neonates)

Neisseria meningitidis is a gram-negative diplococcus bacteria. They are circular bacteria (cocci) that occur in pairs (diplo-). It is commonly known as meningococcus. It is the most common cause of bacterial meningitis.

Meningococcal meningitis is when the bacteria infects the meninges and the cerebrospinal fluid. Meningococcal septicaemia is when the meningococcus bacterial infection is in the bloodstream. Meningococcal septicaemia can cause the classic non-blanching rash.

Question 56

Viral meningitis

Answer 56

The most common causes of viral meningitis are:

Enteroviruses (e.g., coxsackievirus)
Herpes simplex virus (HSV)
Varicella zoster virus (VZV)

Viral PCR testing can be performed on a CSF sample. Aciclovir is used to treat HSV and VZV.

Question 57

Presentation of meningitis

Answer 57

Typical symptoms of meningitis are:

Fever
Neck stiffness
Vomiting
Headache
Photophobia
Altered consciousness
Seizures

Where there is meningococcal septicaemia, children can present with a non-blanching rash. Other causes of bacterial meningitis do not usually cause the non-blanching rash.

Neonates and babies can present with non-specific signs and symptoms, such as hypotonia, poor feeding, lethargy, hypothermia and a bulging fontanelle. The NICE guidelines on sepsis recommend lumbar puncture as part of the investigations for children with suspected sepsis who are:

Under 1 month, presenting with fever
1 to 3 months and are unwell or have a low or high white blood cell count

There are two special tests you can perform to look for meningeal irritation:

Kernig’s test
Brudzinski’s test

Kernig’s test involves lying the patient on their back, flexing one hip and knee to 90 degrees and then slowly straightening the knee whilst keeping the hip flexed at 90 degrees. This creates a slight stretch in the meninges. Where there is meningitis, it will produce spinal pain or resistance to movement.

Brudzinski’s test involves lying the patient flat on their back and gently using your hands to lift their head and neck off the bed, flexing their chin to their chest. A positive test, indicating meningitis, is when this causes the patient to flex their hips and knees involuntarily.

Question 58

Lumbar puncture

Answer 58

A lumbar puncture involves inserting a needle into the lower back to collect a sample of cerebrospinal fluid (CSF). The spinal cord ends at the L1-L2 vertebral level. The needle is usually inserted into the L3-L4 or L4/L5 intervertebral space. Samples are sent for bacterial culture, viral PCR, cell count, protein and glucose. A blood glucose sample is sent at the same time for comparison to the CSF sample. The samples are sent immediately.

Cerebrospinal Fluid
Bacterial
Viral

Appearance
Cloudy
Clear

Protein
High
Mildly raised or normal

Glucose
Low
Normal

White Cell Count
High (neutrophils)
High (lymphocytes)

Culture
Bacteria
Negative

TOM TIP: Lumbar puncture interpretation is a common exam question. Think about what will happen with bacteria or viruses living in the CSF rather than rote learning the results. Bacteria swimming in the CSF will release proteins and use up glucose. Viruses may release a small amount of protein and do not use up glucose. The immune system releases more neutrophils with bacteria and lymphocytes with viruses.

Question 59

Managing bacterial meningitis

Answer 59

Bacterial meningitis is a medical emergency and should be treated immediately.

Children seen in the primary care setting with suspected meningitis and a non-blanching rash should receive an urgent dose of benzylpenicillin (IM or IV) while awaiting transfer to hospital (it should not delay transfer). Where there is a true penicillin allergy, transfer should be the priority rather than other antibiotics. Doses of benzylpenicillin are:

Under 1 year – 300mg
1-9 years – 600mg
Over 10 years – 1200mg

Ideally, blood cultures and a lumbar puncture should be performed before starting antibiotics. However, antibiotics should not be delayed if the patient is acutely unwell.

Blood tests should include a meningococcal PCR if meningococcus is suspected. This tests for meningococcal DNA. It can give a result faster than blood cultures (depending on local services) and will still be positive after the bacteria has been treated with antibiotics.

There should be a low threshold for treating suspected meningitis, particularly in babies and younger children. Always follow the local guidelines. Typical antibiotics are:

Under 3 months – cefotaxime plus amoxicillin (amoxicillin is to cover listeria)
Above 3 months – ceftriaxone

Aciclovir is added if viral meningitis is suspected (mainly herpes simplex virus).

Vancomycin should be added if there is a risk of penicillin-resistant pneumococcal infection (e.g., recent foreign travel or prolonged antibiotic exposure).

Steroids (e.g., dexamethasone) are also used in bacterial meningitis to reduce the frequency and severity of hearing loss and neurological complications.

Bacteria meningitis and meningococcal infection are notifiable diseases to the UK Health Security Agency.

Question 60

Post-exposure prophylaxis and meningitis

Answer 60

Significant exposure to meningococcal infection puts contacts at risk. This risk is highest with close prolonged contact within 7 days before the onset of the illness. The risk to contacts decreases 7 days after the diagnosis.

Post-exposure prophylaxis is guided by the local health protection team when they are notified of the diagnosis. The usual choice is a single dose of ciprofloxacin given as soon as possible after the diagnosis.

Question 61

Complications of meningitis

Answer 61

Hearing loss (a key complication)
Seizures and epilepsy
Cognitive impairment and learning disability
Memory loss
Focal neurological deficits, such as limb weakness or spasticity

Question 62

Tuberculosis

Answer 62

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis, a small rod-shaped bacteria (a bacillus). M. tuberculosis bacteria are very slow dividing and have high oxygen requirements, making them difficult to culture in a lab.

M. tuberculosis has a waxy coating that makes gram staining ineffective. They are resistant to the acids used in the staining procedure, described as “acid-fast”, making them acid-fast bacilli. Special staining is required, using the Zeihl-Neelsen stain, which turns them bright red against a blue background.

TOM TIP: A common exam question involves a patient with a chronic cough and night sweats. Sputum culture grows “acid-fast bacilli” that stain red with “Zeihl-Neelsen staining”. These keywords are worth remembering.

Multidrug-resistant TB (MDR-TB) are strains that are resistant to more than one TB drug (e.g., isoniazid and rifampicin), making them difficult to treat.

Question 63

Disease course of TB

Answer 63

Tuberculosis is mostly spread by inhaling saliva droplets from infected people. Once in the body, there are several possible outcomes:

Immediate clearance of the bacteria (in most cases)
Primary active tuberculosis (active infection after exposure)
Latent tuberculosis (presence of the bacteria without being symptomatic or contagious)
Secondary tuberculosis (reactivation of latent tuberculosis to active infection)

When the immune system cannot control the infection, disseminated and severe disease can develop, referred to as miliary tuberculosis.

Latent tuberculosis is present when the immune system encapsulates the bacteria and stops the progression of the disease. Patients with latent tuberculosis have no symptoms and cannot spread the bacteria. Most otherwise healthy patients with latent tuberculosis never develop an active infection. When latent tuberculosis reactivates, and an infection develops, usually due to immunosuppression, this is called secondary tuberculosis.

The most common site for TB infection is in the lungs, where it gets plenty of oxygen. Extrapulmonary tuberculosis refers to disease in other areas:

Lymph nodes
Pleura
Central nervous system
Pericardium
Gastrointestinal system
Genitourinary system
Bones and joints
Skin (cutaneous tuberculosis)

A cold abscess describes a firm, painless abscess caused by tuberculosis, usually in the neck. They do not have the inflammation, redness and pain you expect from an acutely infected abscess.

Question 64

Risk factors for TB

Answer 64

Close contact with active tuberculosis (e.g., a household member)
Immigrants from areas with high tuberculosis prevalence
People with relatives or close contacts from countries with a high rate of TB
Immunocompromised (e.g., HIV or immunosuppressant medications)
Malnutrition, homelessness, drug users, smokers and alcoholics

Question 65

BCG vaccine

Answer 65

The Bacillus Calmette–Guérin (BCG) vaccine involves an intradermal injection of live attenuated (weakened) Mycobacterium bovis bacteria (a close relative of M. tuberculosis that does not cause disease in humans). This creates an immune response, providing lasting immunity against M. tuberculosis without causing infection. The vaccine protects against severe and complicated TB but less against pulmonary TB.

Before vaccination, patients are tested with the Mantoux test and only given the vaccine if this test is negative. They are also assessed for the possibility of immunosuppression and HIV due to the risks related to a live vaccine.

The BCG vaccine is not part of the routine vaccination schedule. It is offered to patients at increased risk of TB, such as those from areas of high TB prevalence, with close contact with TB (e.g., family members) and healthcare workers.

Question 66

Presentation of TB

Answer 66

Tuberculosis typically presents with chronic, gradually worsening symptoms. Most cases involve pulmonary disease, often with systemic symptoms.

Typical signs and symptoms of tuberculosis include:

Cough
Haemoptysis (coughing up blood)
Lethargy
Fever or night sweats
Weight loss
Lymphadenopathy
Erythema nodosum (tender, red nodules on the shins caused by inflammation of the subcutaneous fat)
Spinal pain in spinal tuberculosis (also known as Pott’s disease of the spine)

Question 67

Investigating TB

Answer 67

Tuberculosis can be challenging to diagnose. The bacteria grow very slowly in a culture, cannot be stained with traditional gram stains and require specialist stains (e.g., Ziehl-Neelsen stain).

There are two tests for an immune response to tuberculosis caused by previous infection, latent TB or active TB:

Mantoux test
Interferon‑gamma release assay (IGRA)

In patients where active disease is suspected, investigations to support the diagnosis include:

Chest x-ray
Cultures

Question 68

Mantoux test

Answer 68

The Mantoux test involves injecting tuberculin into the intradermal space on the forearm. Tuberculin is a collection of tuberculosis proteins isolated from the bacteria. It does not contain any live bacteria.

The infection creates a bleb under the skin. After 72 hours, the test is “read”. This involves measuring the induration of the skin at the injection site. An induration of 5mm or more is considered a positive result.

Interferon-Gamma Release Assays

IGRA involves mixing a blood sample with antigens from the M. tuberculosis bacteria. After previous contact with M. tuberculosis, white blood cells become sensitised to the bacteria antigens and will release interferon-gamma on further contact. A positive result is when interferon-gamma is released during the test.

Question 69

CXR and TB

Answer 69

Primary tuberculosis may show patchy consolidation, pleural effusions and hilar lymphadenopathy.

Reactivated tuberculosis may show patchy or nodular consolidation with cavitation (gas-filled spaces), typically in the upper zones.

Disseminated miliary tuberculosis gives an appearance of millet seeds uniformly distributed across the lung fields.

TOM TIP: Disseminated miliary tuberculosis gives a characteristic appearance of “millet seeds” on a chest x-ray, with many small (1-3mm) nodules disseminated throughout the lung fields. This makes it a popular spot diagnosis in exams. It is worth becoming familiar with the appearance.

Question 70

Cultures and TB

Answer 70

Culture samples are ideally collected before starting treatment. This allows testing for drug resistance. However, cultures can take several months. Treatment is usually started while waiting for the culture results.

There are several ways to collect cultures:

Sputum cultures (3 separate sputum samples are collected)
Mycobacterium blood cultures (require special blood culture bottle)
Lymph node aspiration or biopsy

The NICE guidelines on tuberculosis (2016) describe “deep cough” sputum samples. If they are not producing enough sputum, the options are:

Sputum induction with nebulised hypertonic saline
Bronchoscopy and bronchoalveolar lavage (saline is used to wash the airways and collect a sample)

Question 71

Nucleic Acid Amplification Tests and TB

Answer 71

Nucleic acid amplification tests (NAAT) assess for the genetic material of a pathogen. To detect tuberculosis DNA, NAAT is performed on a sample containing the bacteria (e.g., a sputum sample). It provides information about the bacteria faster than traditional culture, including drug resistance. NAAT is used for:

Diagnosing tuberculosis in patients with HIV or aged under 16
Risk factors for multidrug resistance (where the results would alter management)

Question 72

Treating TB

Answer 72

Latent tuberculosis is treated with either:

Isoniazid and rifampicin for 3 months
Isoniazid for 6 months

The treatment for active tuberculosis can be remembered with the RIPE mnemonic:

R – Rifampicin for 6 months
I – Isoniazid for 6 months
P – Pyrazinamide for 2 months
E – Ethambutol for 2 months

TOM TIP: Remember that isoniazid causes peripheral neuropathy, and pyridoxine (vitamin B6) is co-prescribed to help prevent this. An exam question might say, “…are started on R, I, P and E. What else should be prescribed?” The answer would be pyridoxine or vitamin B6.

Other management options to consider include:

Testing for other infectious diseases (e.g., HIV, hepatitis B and hepatitis C)
Testing contacts for tuberculosis
Notifying UK Health Security Agency (UKHSA) of suspected cases
Isolating patients with active tuberculosis to prevent spread (usually for at least 2 weeks of treatment)
A specialist MDT guides management and follow-up
Individualised regimes are required for multidrug‑resistant tuberculosis and extrapulmonary disease

In hospitals, negative pressure rooms are used to prevent airborne spread. Negative pressure rooms have ventilation systems that actively remove air to prevent it from spreading onto the ward.

Question 73

Side effects of TB treatment

Answer 73

Rifampicin can cause red/orange discolouration of secretions, such as urine and tears. It is a potent inducer of the cytochrome P450 enzymes and reduces the effects of drugs metabolised by this system, such as the combined contraceptive pill.

Isoniazid can cause peripheral neuropathy. Pyridoxine (vitamin B6) is co-prescribed to reduce the risk.

Pyrazinamide can cause hyperuricaemia (high uric acid levels), resulting in gout and kidney stones.

Ethambutol can cause colour blindness and reduced visual acuity.

Rifampicin, isoniazid and pyrazinamide are all associated with hepatotoxicity.

TOM TIP: A common exam question asks “…has recently started treatment for tuberculosis. They notice _____. Which medication is most likely to be implicated?” Numbness or unusual sensations in their feet implicates isoniazide (“I’m-so-numb-azid”). Difficulty recognising colours implicates ethambutol (“eye-thambutol”). Urine or tears that are orange or red implicates rifampicin (“red-I’m-pissin’”).

Question 74

HIV

Answer 74

Being infected with the human immunodeficiency virus (HIV) is referred to as being HIV positive.

Acquired immunodeficiency syndrome (AIDS) occurs when HIV is not treated, the disease progresses, and the person becomes immunocompromised. Immunodeficiency leads to opportunistic infections and AIDS-defining illnesses.

Basics

HIV is an RNA retrovirus. HIV-1 is the most common type. HIV-2 is mainly found in West Africa. The virus enters and destroys the CD4 T-helper cells of the immune system.

An initial seroconversion flu-like illness occurs within a few weeks of infection. The infection is then asymptomatic until the condition progresses to immunodeficiency. Disease progression may occur years after the initial infection.

Question 75

HIV transmission

Answer 75

HIV is not transmitted through day-to-day activities, including kissing. It is spread through:

Unprotected anal, vaginal or oral sexual activity
Mother to child at any stage of pregnancy, birth or breastfeeding (called vertical transmission)
Mucous membrane, blood or open wound exposure to infected blood or bodily fluids (e.g., sharing needles, needle-stick injuries or blood splashed in an eye)

Question 76

AIDS-defining illnesses

Answer 76

There is a long list of AIDS-defining illnesses associated with end-stage HIV infection. These occur where the CD4 count has dropped to a level that allows for unusual opportunistic infections and malignancies to appear.

Examples of AIDS-defining illnesses include:

Kaposi’s sarcoma
Pneumocystis jirovecii pneumonia (PCP)
Cytomegalovirus infection
Candidiasis (oesophageal or bronchial)
Lymphomas
Tuberculosis

Question 77

Screening for HIV

Answer 77

Many people with HIV do not know they are infected, and these patients are at risk of complications and spreading the disease. Generally, the earlier a patient is diagnosed, the better the outcome. HIV is a treatable condition, and most patients are fit and healthy on treatment. There should be a low threshold for HIV testing. Patients with any risk factors should be tested. All patients accessing sexual health, antenatal and substance misuse services are offered testing.

Verbal consent should be documented before a test. However, BHIVA (2023) have draft guidelines for assumed consent (unless the patient voluntarily chooses to opt-out) to HIV screening on blood tests taken in emergency departments (provided posters and leaflets are available).

The fourth-generation laboratory test for HIV checks for antibodies to HIV and the p24 antigen. It has a window period of 45 days, meaning it can take up to 45 days after exposure to the virus for the test to turn positive. A negative result within 45 days of exposure is unreliable. More than 45 days after exposure, a negative result is reliable.

Point-of-care tests for HIV antibodies give a result within minutes. They have a 90-day window period.

Patients at risk of HIV can request home testing kits, either:

Self-sampling kits to be posted to the lab (fourth-generation tests for antibodies and the p24 antigen)
Point-of-care tests (antibodies only)

Question 78

Monitoring HIV

Answer 78

Testing the CD4 count gives the number of CD4 cells in the blood. These are the cells destroyed by the virus. The lower the count, the higher the risk of opportunistic infection:

500-1200 cells/mm3 is the normal range
Under 200 cells/mm3 puts the patient at high risk of opportunistic infections

Testing for HIV RNA per ml of blood indicates the viral load. An undetectable viral load means the level is below the recordable range (usually 20 copies/ml). The viral load can be in the hundreds of thousands in untreated HIV.

Question 79

Treating HIV

Answer 79

Specialist HIV, infectious disease or GUM centres manage patients with HIV.

Treatment involves a combination of antiretroviral therapy (ART) medications. ART is offered to everyone diagnosed with HIV, irrespective of viral load or CD4 count. Some regimes involve only a single combination tablet, taken once daily, with the potential to suppress the infection completely. Genotypic resistance testing can establish the resistance of each HIV strain to different medications to help guide treatment.

There are several classes of antiretroviral therapy medications:

Protease inhibitors (PI)
Integrase inhibitors (II)
Nucleoside reverse transcriptase inhibitors (NRTI)
Non-nucleoside reverse transcriptase inhibitors (NNRTI)
Entry inhibitors (EI)

The usual starting regime is two NRTIs (e.g., tenofovir plus emtricitabine) plus a third agent (e.g., bictegravir).

Treatment aims to achieve a normal CD4 count and undetectable viral load. Generally, when a patient has a normal CD4 and an undetectable viral load on ART, physical health problems (e.g., routine chest infections) are treated the same as those without HIV.

TOM TIP: When prescribing for patients on ART, be aware and carefully check for any medication interactions (hiv-druginteractions.org is a helpful website).

Question 80

Additional management of HIV

Answer 80

Prophylactic co-trimoxazole is given to all HIV positive patients with a CD4 count under 200/mm3 to protect against pneumocystis jirovecii pneumonia (PCP).

HIV infection increases the risk of developing cardiovascular disease. Patients with HIV have close monitoring of cardiovascular risk factors, such as blood lipids. Interventions to reduce the risk (e.g., statins) may be recommended.

Yearly cervical smears are recommended in HIV as it increases the risk of human papillomavirus (HPV) infection and cervical cancer.

Vaccinations should be up to date, including against influenza (yearly), pneumococcal, HPV and hepatitis A and B. Live vaccines (e.g., BCG and typhoid) are avoided.

Question 81

Reproductive health and HIV

Answer 81

Correct use of condoms protects against spreading HIV. Effective treatment combined with an undetectable viral load appears to prevent the spread of HIV, even during unprotected sex (although there is still a risk of other STIs).

Question 82

Preventing transmission of HIV during birth

Answer 82

This information here is an oversimplified illustration of the BHIVA guidelines.

The mother’s viral load will determine the mode of delivery:

Viral Load
Delivery

Under 50 copies/ml
Normal vaginal delivery

Over 50 copies/ml
Consider a pre-labour caesarean section

Over 400 copies/ml
Pre-labour caesarean section is recommended

IV zidovudine is given as an infusion during labour and delivery if the viral load is unknown or above 1000 copies/ml.

Prophylaxis may be given to the baby, depending on the mother’s viral load:

Low-risk babies (mother’s viral load is under 50 copies per ml) are given zidovudine for 2-4 weeks
High-risk babies are given zidovudine, lamivudine and nevirapine for four weeks

Question 83

Breastfeeding and HIV

Answer 83

HIV can be transmitted during breastfeeding. The risk is reduced if the mother’s viral load is undetectable but not eliminated. Therefore, the safest option is to avoid breastfeeding. However, if the mother is adamant and the viral load is undetectable, sometimes it is attempted with close monitoring by the HIV team.

Question 84

Prophylaxis of HIV

Answer 84

Post-exposure prophylaxis (PEP) can be used after exposure to reduce the risk of transmission. PEP is not 100% effective and must be commenced within a short window of opportunity (less than 72 hours). The sooner it is started, the better. A risk assessment of the probability of developing HIV should be balanced against the side effects of PEP.

PEP involves a combination of ART therapy. The current regime is emtricitabine/tenofovir (Truvada) and raltegravir for 28 days.

Pre-exposure prophylaxis (PrEP) is also available to take before exposure to reduce the risk of transmission. The usual choice is emtricitabine/tenofovir (Truvada).

Question 85

Malaria

Answer 85

Malaria is an infectious disease caused by members of the Plasmodium family of protozoan parasites. Protozoa are single-celled organisms. The most severe and dangerous type is Plasmodium falciparum, which accounts for about 80% of malaria cases in the UK.

Malaria is spread through bites from the female Anopheles mosquitoes that carry the disease. Malaria is not transmitted in the UK and is associated with travel to areas where malaria is present.

Question 86

Types of malaria

Answer 86

Plasmodium falciparum (the most common and severe form)
Plasmodium vivax
Plasmodium ovale
Plasmodium malariae
Plasmodium knowlesi

Question 87

Life cycle of malaria

Answer 87

Malaria is spread by female Anopheles mosquitoes, usually at night. A feeding mosquito sucks up infected blood. Then, the parasites reproduce in the mosquito’s gut, producing thousands of sporozoites (malaria spores).

When that mosquito bites someone, the sporozoites are injected. These sporozoites travel to the liver of the newly infected person. P. vivax and P. ovale can lie dormant as hypnozoites for months or years before reactivating.

The malaria parasites mature in the liver into merozoites, which enter the blood and infect red blood cells. In red blood cells, the merozoites reproduce, after which the red blood cells rupture, releasing loads more merozoites into the blood and causing haemolytic anaemia.

For P. vivax and P. ovale, this rupture and release of merozoites occurs every 48 hours, causing a fever spike every other day. A fever every 48 hours is referred to as tertian malaria. P. falciparum has more frequent (“subtertian“) or irregular fever spikes, and P. malariae has spikes every 72 hours (“quartan“).

Question 88

Presentation of malaria

Answer 88

Malaria should be suspected in someone that has travelled to an area where malaria is present. The incubation period is usually 1-4 weeks after exposure, although it can lie dormant for years.

Many of the symptoms are non-specific:

Fever (up to 41ºC) with sweats and rigors
Fatigue
Myalgia (muscle aches and pain)
Headache
Nausea
Vomiting

Signs on examination include:

Pallor due to the anaemia
Hepatosplenomegaly
Jaundice (bilirubin is released during the rupture of red blood cells)

TOM TIP: The most characteristic symptom of malaria is the fever, which spikes very high every 48 hours. In someone with an unexplained fever, consider whether they have travelled somewhere with malaria present. Even exposure several years ago may be relevant, as P. vivax and P. ovale can lie dormant for up to 4 years.

Question 89

Diagnosing malaria

Answer 89

The diagnosis is made using a malaria blood film. This is sent in an EDTA bottle (the same bottle used for a full blood count). A malaria blood film will show the parasites, the concentration (as a percentage) and the type.

Three negative samples taken over three consecutive days are required to exclude malaria due to the parasites being released from red blood cells into the blood every 48-72 hours. The sample may be negative when the parasites are not released but positive a day or two later when the red blood cells rupture and release the parasites.

Question 90

Managing malaria

Answer 90

The local infectious diseases team will advise on management. All patients with falciparum malaria are admitted.

Oral options for uncomplicated malaria include:

Artemether with lumefantrine (Riamet) is the usual first choice
Quinine plus doxycycline
Quinine plus clindamycin
Proguanil with atovaquone (Malarone)
Chloroquine (there are increasing rates of resistance to chloroquine)
Primaquine (can cause severe haemolysis in patients with G6PD deficiency)

Severe or complicated malaria often requires admission to HDU or ICU. Intravenous treatment options include:

Artesunate is the usual first choice (haemolysis is a common side effect)
Quinine dihydrochloride

TOM TIP: Remember artesunate and quinine as treatment options for your exams, as these are the most likely to be relevant. Remember that Plasmodium falciparum is the most common and severe cause, and these patients should be admitted for artesunate treatment and monitoring for complications.

Question 91

Complications of P. falciparum malaria

Answer 91

There is a long list of complications of P. falciparum malaria, including:

Cerebral malaria
Seizures
Reduced consciousness
Acute kidney injury
Pulmonary oedema
Disseminated intravascular coagulopathy (DIC)
Severe haemolytic anaemia
Multi-organ failure and death

Question 92

Prophylaxis and malaria

Answer 92

General advice for preventing malaria when travelling to endemic areas:

No method is 100% effective alone
Use mosquito spray (e.g., 50% DEET spray)
Use mosquito nets and barriers in sleeping areas
Seek medical advice if symptoms develop
Take antimalarial medication as recommended

Antimalarial medications are not 100% effective. The main options are:

Proguanil with atovaquone (Malarone)
Doxycycline
Mefloquine (risk of psychiatric side effects)
Chloroquine with proguanil (less often used due to high resistance)

Proguanil / atovaquone (Malarone) is slightly more expensive than the other options but has the least side effects. It is taken from two days before until seven days after travel to an endemic area.

Doxycycline is a broad-spectrum antibiotic that can cause side effects such as diarrhoea and thrush. It also causes skin sensitivity to sunlight, increasing the risk of sunburn and skin reactions. It is taken two days before until four weeks after travel to an endemic area.

Mefloquine is associated with psychiatric side effects, such as anxiety, depression and abnormal dreams. Rarely it can cause psychosis or seizures. It is taken weekly, from two weeks before until four weeks after travel to an endemic area.

Question 93

Alpha-hemolytic strep eg pneumoniae, viridans, cause partial hemolysis Beta-hemolytic strep eg Group A Strep (pyogenes), or Group B strep (agalactiae) cause complete hemolysis on agar

Question 94

The characteristic rash of measles does not normally start until after a few days of fever, where it begins on the back of the head and behind the ears. The early course of measles can be thought of as the 4Ds (4 days of fever) and the 3Cs (cough, coryza, conjunctivitis).