Infectious Disease Flashcards

Question

Septic arthritis

Answer 1

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.

Answer 2

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

Answer 3

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).

Answer 4

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)

Answer 5

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.

Answer 6

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.

Answer 7

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

Answer 8

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.

Answer 9

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.

Answer 10

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

Answer 11

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

Answer 12

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.

Answer 13

Viral gastroenteritis is common. It is highly contagious. Specific viruses include: Rotavirus Norovirus Adenovirus (tends to cause respiratory symptoms)

Answer 14

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.

Answer 15

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.

Answer 16

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.

Answer 17

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).

Answer 18

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.

Answer 19

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.

Answer 20

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.

Answer 21

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.

Answer 22

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.

Answer 23

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

Answer 24

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.

Answer 25

The antibiotics most associated with C. difficile start with the letter C: Clindamycin Ciprofloxacin (and other fluoroquinolones) Cephalosporins Carbapenems (e.g., meropenem)

Answer 26

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)

Answer 27

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.

Answer 28

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.

Answer 29

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.

Answer 30

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).

Answer 31

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.

Answer 32

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.

Answer 33

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.

Answer 34

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.

Answer 35

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.

Answer 36

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.

Answer 37

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

Answer 38

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.

Answer 39

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.

Answer 40

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

Answer 41

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.

Answer 42

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)

Answer 43

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

Answer 44

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.

Answer 45

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.

Answer 46

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)

Answer 47

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)

Answer 48

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.

Answer 49

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’”).

Answer 50

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.

Answer 51

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)

Answer 52

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

Answer 53

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)

Answer 54

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.

Answer 55

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).

Answer 56

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.

Answer 57

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).

Answer 58

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

Answer 59

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.

Answer 60

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).

Answer 61

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.

Answer 62

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

Answer 63

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“).

Answer 64

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.

Answer 65

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.

Answer 66

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.

Answer 67

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

Answer 68

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.