Infectious Disease

Oliver Hart

Welcome to the Infectious Disease podcast. This episode aims to recap all of the important aspects of each topic so that you feel confident in your knowledge.

Alys Davies

We’ve split the episode into two parts. First, we will go through a topic breakdown. Then we will move into our rapid-recall question round, a section where we test your knowledge on the topics we have covered in the episode.

Oliver Hart

There are ten Infectious Disease topics to cover in this episode, with tips and reminders dotted throughout.

Alys Davies

If you are using this podcast as revision for upcoming exams, please look on official websites for specifics on question weighting and structure. In this podcast, we will be explaining each topic through realistic clinical scenarios, similar to questions you’ll encounter in exams and real clinical situations.

Oliver Hart

So, let’s get started.

Oliver Hart

Our first topic is Tuberculosis, known as the shorthand TB. We are going to cover it in three parts: how to diagnose it, how to treat it, and which drug causes which side effect.

Alys Davies

TB is caused by Mycobacterium tuberculosis, an aerobic acid-fast bacillus transmitted by airborne droplets. Primary infection is usually subclinical. The immune system walls the bacteria off before any symptoms appear. What we see clinically is almost always reactivation, often years or decades later. The classic presentation is a cough lasting more than three weeks, haemoptysis, weight loss, night sweats, and low-grade fever. On chest X-ray, look for upper lobe cavitation, consolidation, and hilar lymphadenopathy.

Oliver Hart

Diagnosis depends on the clinical setting. Sputum AFB smear is the fastest test, with three samples to be sent on consecutive days. This is less sensitive but widely available. A culture test takes longer because mycobacteria grow slowly, but it identifies drug resistance. Nucleic acid amplification testing (NAAT or GeneXpert) gives a rapid result and can simultaneously detect rifampicin resistance.

Alys Davies

Latent TB is a separate situation. The bacteria are dormant, so sputum and imaging are unhelpful. Instead, you test the immune response. The Mantoux test injects tuberculin protein and measures the skin reaction at 48 to 72 hours. Its main limitation is that it is positive after BCG vaccination, which makes it unreliable in vaccinated patients. The IGRA, interferon-gamma release assay, commercially known as QuantiFERON, is more specific because it uses TB antigens that are not present in BCG. It is unaffected by vaccination status.

Oliver Hart

Active TB is treated with four drugs for the first two months, memorable by the mnemonic RIPE. R, Rifampicin; I, Isoniazid; P, Pyrazinamide; and E, Ethambutol. All four drugs are given for the first two months. Treatment then steps down to rifampicin and isoniazid for a further four months. The total course is six months.

Alys Davies

Each drug in RIPE has a distinct side effect profile. Rifampicin is a potent liver enzyme inducer, which means it reduces the effectiveness of many other drugs, including the oral contraceptive pill. It’s best if patients are counselled about this. It also causes hepatotoxicity. The less serious, but still alarming, effect is the body fluids turning orange. Patients need to be warned so they are not frightened by it.

Oliver Hart

Isoniazid causes peripheral neuropathy through vitamin B6 depletion. Pyridoxine (B6) is always prescribed alongside it to prevent this. Isoniazid also causes hepatotoxicity and can trigger a drug-induced lupus-like syndrome. Pyrazinamide reduces renal uric acid clearance, which raises serum urate and can precipitate gout. It is also hepatotoxic.

Alys Davies

Ethambutol causes optic neuritis. Because this is a visual complication, visual acuity and colour vision must be checked before starting treatment and monitored throughout. Ethambutol is contraindicated in young children who cannot reliably report changes in their vision.

Oliver Hart

Latent TB is treated with fewer drugs over a shorter course. The three options are: isoniazid alone for six months, isoniazid plus rifampicin for three months, or rifampicin alone for four months. The choice depends on drug tolerability and patient preference.

Alys Davies

TB can spread haematogenously to almost any organ, and each site has distinguishing features. Lymph node involvement is the most common extrapulmonary form, presenting as enlarged, matted nodes, often cervical. Pleural TB gives an exudative, lymphocytic effusion. Pericardial TB is treated using the RIPE mnemonic, plus corticosteroids to reduce the risk of constrictive pericarditis. And lastly, skeletal TB (also known as Pott's Disease) most commonly affects the lower thoracic spine.

Oliver Hart

Genitourinary TB causes sterile pyuria and is tested with white cells on a urine dipstick with no growth on standard culture. TB-specific culture is needed for diagnosis. TB meningitis gives CSF lymphocytic pleocytosis, presenting as very low glucose and raised protein. Treatment starts with RIPE, plus dexamethasone. Also, be aware that TB is a notifiable disease in the UK and contact tracing is mandatory.

Alys Davies

Remember, Ethambutol causes optic neuritis; check visual acuity and colour vision before starting and monitor during treatment. This is the side effect most commonly tested in exams.

Alys Davies

Our second topic is HIV. We are going to cover staging, what each stage means clinically, the CD4 thresholds that determine prophylaxis decisions, and how antiretroviral therapy works. These three elements are closely linked, understanding one makes the others much easier to follow.

Oliver Hart

HIV is an RNA retrovirus that targets CD4-positive T-lymphocytes. Transmission in the UK is most commonly sexual. Though, blood-borne transmission through needle-sharing can still occur. Vertical transmission from mother to child can also occur during pregnancy, delivery, or breastfeeding.

Alys Davies

WHO staging runs from one to four and tracks the progressive destruction of CD4 cells. Stage one is asymptomatic. Stage two brings minor problems, mucocutaneous conditions and recurrent upper respiratory tract infections. Stage three involves significant immunosuppression: severe weight loss, chronic diarrhoea, oral candidiasis, and pulmonary TB. Stage four is AIDS, defined by a CD4 count below 200 or the presence of an AIDS-defining illness.

Oliver Hart

AIDS-defining illnesses are conditions that occur when immunity has failed to a critical level, allowing pathogens that a healthy immune system would clear without difficulty. They include: Pneumocystis jirovecii pneumonia (known as PCP), CMV retinitis, cerebral toxoplasmosis, cryptococcal meningitis, oesophageal candidiasis, Kaposi's sarcoma, Mycobacterium avium complex (known as MAC), and CNS lymphoma.

Alys Davies

The CD4 count determines which prophylactic treatments should be started. The thresholds also commonly come up in exams. Below 500: the risk of TB and bacterial pneumonia rises, no prophylaxis is started at this level, but vigilance increases. Below 200: start PCP prophylaxis with co-trimoxazole. Below 100: add toxoplasma prophylaxis, also co-trimoxazole, and cryptococcal meningitis becomes a significant risk. Below 50: start MAC prophylaxis with azithromycin, and CMV retinitis becomes a major concern.

Oliver Hart

PCP is worth understanding in detail because it appears frequently. Pneumocystis jirovecii is a fungus that causes severe pneumonia in patients with CD4 below 200. The presentation is a dry cough, progressive breathlessness, and bilateral perihilar infiltrates on a chest X-ray. LDH is elevated, reflecting lung tissue damage. Treatment is high-dose co-trimoxazole intravenously. If the PaO2 is below 9.3 kilopascals, add prednisolone. Steroids reduce the inflammatory response that cause much of the lung damage.

Alys Davies

ART uses at least three drugs with different mechanisms simultaneously. This is because HIV replicates rapidly and mutates constantly. A single drug would quickly select for resistant variants. All HIV-positive patients should be offered the standard regimen is two NRTIs, typically tenofovir plus emtricitabine, combined with an integrase strand transfer inhibitor, or INSTI. Dolutegravir is the most commonly used INSTI and is now first-line.

Oliver Hart

The treatment goal is an undetectable viral load, below 50 copies per millilitre. When this is achieved, the virus is untransmittable. This is the basis of the U equals U campaign: undetectable equals untransmittable. Patients with HIV who are well-controlled on ART can hold a driving licence. HIV does not automatically disqualify a patient from driving.

Oliver Hart

Remember. If CD4 is below 200, start PCP prophylaxis with co-trimoxazole. If CD4 is below 50, start MAC prophylaxis with azithromycin. These thresholds are directly tested in exams, so remember these two CD4 numbers.

Oliver Hart

Topic three is EBV and CMV. We will look at how to distinguish them clinically, what their complications are, and one important drug interaction that catches students out.

Alys Davies

EBV, known as Epstein-Barr virus, causes infectious mononucleosis, also called glandular fever. It spreads through saliva and is most common in young adults. The classic triad is fever, exudative tonsillitis, and lymphadenopathy, typically posterior cervical. Splenomegaly occurs in about fifty per cent of cases, which creates a risk of splenic rupture.

Oliver Hart

The blood film shows atypical lymphocytes. These are reactive T-cells responding to the infection, not the infected cells themselves. The Monospot test detects heterophile antibodies and is positive in about eighty-five per cent of adults, but it is unreliable in children under four. EBV-specific antibodies give more precision: VCA IgM is positive in acute infection, and EBNA antibodies only appear after three or more months, so their presence suggests past rather than current infection.

Alys Davies

Complications include splenic rupture, so advise patients to avoid contact sports for four weeks. Other complications are haemolytic anaemia, thrombocytopaenia, Guillain-Barré syndrome, and encephalitis.

Oliver Hart

Now, drug interaction. If a patient with EBV receives amoxicillin or ampicillin, approximately ninety per cent will develop a widespread maculopapular rash. This is not a penicillin allergy, it is a pharmacological interaction specific to the context of EBV infection.

Alys Davies

CMV in the immunocompetent is usually asymptomatic. When it does cause symptoms, it produces a mononucleosis-like illness with less pharyngitis and more prominent hepatitis, and the Monospot test is negative. This is the key distinguishing feature: mononucleosis symptoms plus a negative Monospot should point you towards CMV rather than EBV.

Oliver Hart

In immunocompromised patients, particularly those with HIV and CD4 below 50, CMV causes retinitis, pneumonitis, and colitis. Diagnosis is by CMV PCR. Treatment is ganciclovir intravenously or valganciclovir orally.

Oliver Hart

Remember. In EBV, amoxicillin or ampicillin causes a rash in approximately 90% of cases. This is not a penicillin allergy; do not label the patient as penicillin allergic on this basis.

Alys Davies

Topic four is malaria. In this topic, we are going to cover the five species, why the distinction between each matters, clinical features and diagnosis, the criteria for severe disease, treatment, and chemoprophylaxis.

Oliver Hart

There are five species that infect humans, and they all share the same vector, the Anopheles mosquito, but they differ significantly in severity and behaviour. Plasmodium falciparum is the most dangerous, causing the majority of malaria deaths, and it is the dominant species in sub-Saharan Africa. Plasmodium vivax is the most widespread globally. Plasmodium ovale behaves similarly to vivax. Both vivax and ovale have dormant liver forms (hypnozoites) that can reactivate and cause relapsing malaria. Plasmodium malariae is the most indolent and can persist in the bloodstream for decades. Plasmodium knowlesi is found in South-East Asia, is a zoonosis from macaques, and can cause severe disease because it cycles rapidly.

Alys Davies

Incubation periods matter for the differential diagnosis. Falciparum typically presents within seven to fourteen days of exposure, though it can be up to three months. Vivax and ovale can present up to twelve months later due to hypnozoite reactivation. This is why you must take a travel history going back at least a year, not just the last few weeks.

Oliver Hart

The presenting features of malaria are non-specific: fever, headache, myalgia, and rigors, which is why it is easily missed. The classical pattern of paroxysmal fever at regular intervals is less reliable in practice, particularly with falciparum. The clinical rule is: send a malaria film for any returning traveller with a fever, regardless of whether they took prophylaxis.

Alys Davies

Thick and thin blood films identify the species and quantify the parasitaemia. Rapid antigen tests detect P. falciparum HRP2 antigen quickly when microscopy is not immediately available. If the initial film is negative, repeat it at twelve to twenty-four hour intervals for at least three days, parasitaemia can be too low to detect early in the illness. A single negative film does not rule out malaria.

Oliver Hart

Severe malaria is caused by falciparum and requires intravenous treatment. The WHO criteria include: cerebral malaria with altered consciousness, severe anaemia below eight grams per decilitre, respiratory distress, hypoglycaemia below 2.2 millimoles per litre, acute kidney injury, circulatory collapse, abnormal bleeding, and hyperparasitaemia — defined as more than five per cent of red blood cells infected.

Alys Davies

For uncomplicated falciparum in the UK, the first-line options are artemether-lumefantrine or dihydroartemisinin-piperaquine. These are artemisinin-based combination therapies. For non-falciparum malaria, vivax or ovale, chloroquine treats the blood stage, but primaquine is also needed to eradicate the hypnozoites from the liver and prevent relapse. Before prescribing primaquine, always check G6PD status. G6PD deficiency is X-linked and primaquine causes haemolysis in affected individuals.

Oliver Hart

For severe malaria, IV artesunate is first-line. Quinine plus doxycycline is used only if artesunate is unavailable.

Alys Davies

The choice of prophylaxis depends on the destination and the patient. Atovaquone-proguanil (Malarone) is started one to two days before travel and continued for seven days after return. Doxycycline starts one to two days before and continues for twenty-eight days after — warn patients about photosensitivity. Mefloquine is started three weeks before departure. The long lead time is deliberate — it allows assessment for neuropsychiatric side effects, such as vivid dreams, anxiety, and depression, while the patient is still at home. Continue for four weeks after return. Mefloquine is contraindicated in epilepsy, psychiatric illness, and cardiac conduction defects.

Oliver Hart

Remember. Severe malaria is treated with 4 artesunate, not quinine. Artesunate is first-line. Hyperparasitaemia above 5% infected red blood cells defines severe malaria regardless of other clinical features.

Oliver Hart

Topic five is enteric fever — an Amber topic. The key framework here is the week-by-week progression, because it determines which investigations to use at each stage. That is the part that comes up most often in exams.

Alys Davies

Enteric fever is caused by Salmonella typhi (typhoid) and Salmonella paratyphi (paratyphoid). Both are transmitted by the faecal-oral route through contaminated food or water. Incubation is seven to twenty-one days.

Oliver Hart

In the first week, the bacteria are circulating in the bloodstream. The fever rises in a stepwise pattern, a little higher each day. There is relative bradycardia, the pulse is inappropriately slow for the temperature, which is the classic pulse-temperature dissociation. Rose spots appear in about thirty per cent of patients: faint salmon-coloured macules on the trunk, very transient and easy to miss. Splenomegaly and a dry cough are also seen.

Alys Davies

In the second week, the fever plateaus and the bacteria begin to seed the gastrointestinal tract. In the third week, the most dangerous complications occur — intestinal perforation and haemorrhage from necrosis of the Peyer's patches in the terminal ileum. A patient with enteric fever who develops an acute abdomen needs urgent surgical assessment.

Oliver Hart

The investigation approach changes each week because the bacteria move between compartments. In week one, they are in the bloodstream. Blood cultures are the investigation of choice, positive in approximately eighty per cent of cases. In week two, send both blood cultures and stool cultures. By week three, stool and urine cultures become more reliable as blood culture positivity falls. Bone marrow culture is the most sensitive investigation at all stages, around ninety per cent, but it is invasive and rarely used in practice.

Alys Davies

The Widal test is unreliable. False positives are common in endemic areas and after typhoid vaccination. It should not be relied upon for diagnosis.

Oliver Hart

Ceftriaxone intravenously is the most reliable first-line treatment, particularly when sensitivity data are not yet available, because fluoroquinolone resistance is now widespread, especially from South Asia. Azithromycin orally is an alternative for uncomplicated disease. Ciprofloxacin should only be used if susceptibility is confirmed.

Alys Davies

Complications beyond perforation and haemorrhage include hepatitis, cholecystitis, and myocarditis. Chronic carriage occurs in the gallbladder, particularly in patients with gallstones, and these individuals can shed Salmonella typhi in their faeces for years without symptoms. Enteric fever is a notifiable disease.

Alys Davies

Remember. Blood cultures are most sensitive in the first week of enteric fever, positive in approximately 80% of cases. In week three, stool and urine cultures are more reliable. For exams, it may be useful to know the week-by-week framework.

Alys Davies

Topic six covers two related clinical scenarios: the patient with a prolonged unexplained fever, and the patient who has returned from abroad unwell. Both require a systematic approach, and both have specific frameworks that come up in exams.

Oliver Hart

Fever of unknown origin has a specific definition. It requires a fever above 38.3 degrees Celsius on multiple occasions, lasting more than three weeks, with no diagnosis after one week of thorough in-hospital investigation. The emphasis on in-hospital investigation is important; FUO means you have already done the basic workup and it remains unexplained.

Alys Davies

The causes fall into four categories. Infections account for thirty to forty per cent of cases; TB, abscesses, endocarditis, CMV, and EBV are the most common. Malignancy accounts for twenty to thirty per cent, lymphoma is the classic, along with renal cell carcinoma and hepatoma. Non-infectious inflammatory diseases include adult-onset Still's, SLE, vasculitis, and sarcoidosis. And drug fever, caused by many agents, including allopurinol, hydralazine, phenytoin, and sulphonamides, is easy to overlook.

Oliver Hart

Adult-onset Still's has a distinctive clinical picture. The fever is quotidian; it spikes once or twice daily and returns to normal. A salmon-coloured rash appears with the fever and fades when the temperature settles. Arthritis, sore throat, and lymphadenopathy are also present. The key laboratory clue is a markedly elevated serum ferritin, above ten thousand micrograms per litre is highly suggestive. No other diagnosis in the FUO differential regularly produces ferritin at that level.

Alys Davies

Investigation should be systematic and layered. Start with blood cultures times three, FBC, CRP, ESR, LFTs, LDH, and serum ferritin. Add immunology: ANA, ANCA, and rheumatoid factor. Send IGRA or Mantoux for TB, and CMV and EBV serology. Imaging: CT of the chest, abdomen, and pelvis to look for lymphadenopathy, occult malignancy, and abscess. PET-CT is increasingly used when standard imaging is unrevealing. It can detect occult malignancy and large vessel vasculitis that CT misses.

Oliver Hart

For the febrile returning traveller, use the ABCDE framework to structure the history. A - Area: which country, and rural or urban? B- Bites: mosquitoes, ticks, sandflies, animals? C - Contact: freshwater exposure, animal contact, person-to-person? D - Diet: food and water sources? E - Exposure: sexual contact, healthcare work, humanitarian work in endemic areas?

Alys Davies

Malaria must always be excluded first in a febrile traveller from an endemic area, even if they took prophylaxis; no prophylaxis is one hundred per cent effective. Common causes vary by region: Sub-Saharan Africa: malaria, typhoid, dengue. South and South-East Asia: dengue, typhoid, malaria, leptospirosis. Latin America: dengue, malaria, chikungunya, leptospirosis.

Oliver Hart

Dengue is transmitted by the Aedes mosquito and has no specific antiviral and management is supportive. The key blood findings are thrombocytopaenia and a raised haematocrit due to haemoconcentration. Dengue haemorrhagic fever and dengue shock syndrome are the severe forms, managed by careful fluid balance.

Alys Davies

Remember. Malaria must always be excluded first in a febrile returning traveller, even if they took prophylaxis. A single negative film does not rule it out. Repeat at 12–24 hour intervals.

Oliver Hart

Topic seven is another Amber topic. The approach in exams is to give you a clinical scenario and ask you to identify the organism. So for each pathogen, focus on the exposure history, the distinguishing clinical feature, and the treatment.

Alys Davies

Leishmaniasis is caused by Leishmania species and transmitted by sandfly bites. There are three clinical forms. Cutaneous leishmaniasis causes a painless ulcer with a raised, indurated border and a central depression, sometimes described as a volcano-crater appearance. Mucocutaneous leishmaniasis spreads to the mucous membranes of the nose and pharynx, causing progressive destruction. Visceral leishmaniasis, kala-azar, is the most severe: the parasite invades macrophages in the liver, spleen, and bone marrow, causing massive splenomegaly, fever, weight loss, pancytopenia, and dark skin discolouration. Diagnosis of visceral disease is by splenic or bone marrow aspirate, or serology. Treatment is liposomal amphotericin B.

Oliver Hart

Schistosomiasis is acquired through freshwater exposure in sub-Saharan Africa, South-East Asia, and the Middle East. The larvae, cercariae, penetrate the skin directly. An acute phase called Katayama fever occurs four to eight weeks after exposure, with fever, urticaria, and eosinophilia. Chronic disease depends on the species. Schistosoma haematobium affects the bladder, causing chronic haematuria and an association with squamous cell carcinoma of the bladder. Schistosoma mansoni and japonicum cause hepatosplenic disease and portal hypertension through granuloma formation around eggs trapped in the liver. Diagnosis is by finding ova in urine or stool, or by serology. Treatment is praziquantel.

Alys Davies

Strongyloides stercoralis has one feature that sets it apart from other helminths: it can autoinfect. The larvae reinfect the host directly from the gut without leaving the body. This means an infection acquired decades ago can still be active. In the immunocompetent, it causes chronic low-level infection, often eosinophilia and a migratory skin rash called larva currens, without severe symptoms.

Oliver Hart

In immunocompromised patients, particularly those on corticosteroids or with HTLV-1 infection, the autoinfection accelerates into hyperinfection syndrome. Larvae breach the gut wall in large numbers, carrying gram-negative gut bacteria with them. The result is gram-negative bacteraemia and meningitis, which can be fatal. The practical lesson: screen patients from endemic areas with Strongyloides serology before starting any immunosuppression. Diagnosis in routine cases is by stool microscopy for larvae, not ova, or serology. Treatment is ivermectin.

Alys Davies

Toxoplasma gondii is an intracellular parasite acquired from cat faeces or undercooked meat. Primary infection in the immunocompetent is usually asymptomatic. Dormant cysts persist in the brain and muscle for life without causing harm. In HIV patients with CD4 below 100, these cysts reactivate and cause cerebral toxoplasmosis, presenting with headache, focal neurological deficits, and seizures. Imaging shows ring-enhancing lesions on CT or MRI. Treatment is pyrimethamine plus sulfadiazine plus folinic acid. Prophylaxis with co-trimoxazole is started when CD4 falls below 100, which also covers PCP.

Oliver Hart

Remember. Strongyloides hyperinfection is a life-threatening complication in immunocompromised patients. Screen with serology before starting corticosteroids or immunosuppression in anyone from an endemic area.

Alys Davies

Topic eight is Amber and covers two distinct clinical scenarios. The first is pre-travel assessment, advising a patient before they go abroad. The second is migrant health screening, assessing a patient who has arrived from a high-prevalence region.

Oliver Hart

Pre-travel assessment should cover five areas: vaccines, both routine and travel-specific; malaria chemoprophylaxis; food and water safety; insect bite precautions, including repellent with DEET; and travel insurance that covers medical evacuation.

Alys Davies

Hepatitis A is the most commonly required travel vaccine, recommended for most non-Western destinations. Typhoid can be given as an oral live vaccine, Vivotif, or as an injectable polysaccharide vaccine, ViCPS. The oral form is live, so it is contraindicated in immunocompromised patients.

Oliver Hart

Yellow fever vaccine gets particular attention in exams because of its contraindications. It is a live attenuated vaccine required for entry to certain countries in sub-Saharan Africa and South America. It is absolutely contraindicated in immunocompromised patients, including those on high-dose corticosteroids, chemotherapy, or with HIV and CD4 below 200. It is also relatively contraindicated in patients over sixty years old, because the risk of vaccine-associated viscerotropic disease, a severe systemic illness mimicking yellow fever itself, increases with age. Patients over sixty who require the vaccine should be referred for specialist assessment. Meningococcal ACWY vaccine is recommended for Hajj pilgrimage and travel to the meningitis belt in sub-Saharan Africa.

Alys Davies

The timing of each prophylaxis agent is important. Atovaquone-proguanil (Malarone) is started one to two days before travel and continued for seven days after return. This short window makes it suitable for last-minute trips. Doxycycline starts one to two days before but continues for twenty-eight days after return; warn about photosensitivity. Mefloquine must be started three weeks before departure. This lead time is deliberate: it allows assessment for neuropsychiatric side effects while the patient is still at home. Continue for four weeks after return. Contraindications to mefloquine include epilepsy, psychiatric illness, and cardiac conduction defects.

Oliver Hart

Patients who have migrated from high-prevalence regions should be offered systematic screening, because many chronic infections are asymptomatic for years but cause serious complications if left untreated. The screen should include: TB with an IGRA and chest X-ray; blood-borne virus screening for HIV, hepatitis B, and hepatitis C; sexually transmitted infection screening; Strongyloides serology for patients from tropical regions; schistosomiasis serology for those from sub-Saharan Africa; and malaria testing in any symptomatic patient from an endemic area.

Alys Davies

Remember. Yellow fever vaccine is contraindicated in immunocompromised patients and in those over 60 without specialist assessment. The risk of vaccine-associated viscerotropic disease increases with age.

Oliver Hart

Topic nine is sexually transmitted infections. The approach in exams is consistent: you are given a clinical presentation and asked to name the organism, choose the right investigation, and identify the first-line treatment. We will cover gonorrhoea, chlamydia, syphilis, herpes, and HPV.

Alys Davies

Gonorrhoea is caused by Neisseria gonorrhoeae. In men, it causes purulent urethral discharge and dysuria. In women, it is often asymptomatic — which is why it is frequently identified through partner notification rather than symptoms. Pharyngeal and rectal infections are also often asymptomatic. Disseminated gonococcal infection presents with migratory polyarthritis, tenosynovitis, and a pustular rash on the extremities. Diagnosis: NAAT is the most sensitive method; culture is used for antibiotic sensitivity testing. Treatment per BASHH guidelines: ceftriaxone one gram intramuscularly as a single dose. Dual therapy with azithromycin is no longer recommended due to rising resistance.

Oliver Hart

Chlamydia trachomatis is the most common bacterial STI in the UK. It is usually asymptomatic, which is why it goes untreated for months or years and causes long-term complications. In women, ascending infection causes pelvic inflammatory disease, ectopic pregnancy, and infertility. In men, it causes epididymo-orchitis. In both sexes, it can trigger reactive arthritis — the triad of urethritis, arthritis, and conjunctivitis, previously called Reiter's syndrome. Diagnosis: NAAT. Treatment: doxycycline 100 milligrams twice daily for seven days.

Alys Davies

Syphilis is caused by Treponema pallidum. It is staged, and each stage has distinct clinical features. Primary syphilis presents as a painless ulcer, the chancre, at the site of inoculation, with inguinal lymphadenopathy. The painlessness is the key feature. It heals spontaneously in three to six weeks.

Oliver Hart

Secondary syphilis appears six to eight weeks later and represents haematogenous spread. The hallmark is a generalised maculopapular rash that classically involves the palms and soles. This is the clue in the exam vignette. Other features include condylomata lata, mucous patches in the mouth, flu-like illness, and lymphadenopathy. Secondary syphilis is the most infectious stage. Latent syphilis means serology is positive, but the patient has no symptoms. Early latent is within two years of infection; late latent is beyond two years.

Alys Davies

Tertiary syphilis has three main manifestations. Gummas are granulomatous lesions that can appear in any organ. Cardiovascular syphilis causes aortitis, leading to aortic regurgitation and ascending aortic aneurysm. Neurosyphilis causes tabes dorsalis, degeneration of the posterior columns producing a wide-based gait and loss of proprioception and general paresis. The Argyll Robertson pupil is the classic sign: it accommodates but does not react to light.

Oliver Hart

Serology has two components. Treponemal tests (TPPA, TPHA, and FTA-ABS) are specific and remain positive for life even after treatment, so they confirm past or current infection but cannot monitor response. Non-treponemal tests, VDRL and RPR, correlate with disease activity and fall with successful treatment, so they are used to monitor response. Treatment: benzathine penicillin G intramuscularly — a single dose for primary and secondary syphilis, and three weekly doses for latent and tertiary disease.

Alys Davies

Herpes simplex (HSV-1 and HSV-2) causes painful genital vesicles and ulcers, dysuria, and inguinal lymphadenopathy. The pain distinguishes it from the painless syphilitic chancre. Diagnosis: NAAT swab from the lesion. Treatment for the first episode: aciclovir 400 milligrams three times daily for five to seven days. Suppressive therapy is used for frequent recurrences.

Oliver Hart

HPV causes two distinct clinical problems depending on type. Low-risk types, six and eleven, cause anogenital warts. High-risk types, sixteen and eighteen, cause cervical, anal, and oropharyngeal cancers. Prevention is through the Gardasil 9 vaccine, which covers types six, eleven, sixteen, eighteen, and five additional high-risk oncogenic types.

Oliver Hart

Remember. The syphilis rash classically involves the palms and soles. The Argyll Robertson pupil accommodates but does not react to light, it is the pupil of neurosyphilis.

Oliver Hart

Topic ten is HIV prevention. We are covering PEP and PrEP, what they are, who they are for, what the time windows are, and what monitoring they require. The distinction between the two is important: PEP is reactive, used after a specific exposure. PrEP is proactive, taken regularly by people with ongoing risk.

Alys Davies

PEP must be started within seventy-two hours of exposure, and the sooner the better, ideally within twenty-four hours. It is given for twenty-eight days and reduces transmission risk by approximately eighty per cent when started promptly. After seventy-two hours, PEP is not indicated.

Oliver Hart

Eligibility is based on the exposure type and the source's HIV status. High-risk exposures to a known HIV-positive source always warrant PEP: these include unprotected anal or vaginal intercourse and needlestick injury with HIV-positive blood. The regimen is tenofovir DF plus emtricitabine, combined with either raltegravir or darunavir plus ritonavir, for twenty-eight days. Starter packs are available from GUM clinics and emergency departments. Patients do not need to wait for a GUM appointment to begin.

Alys Davies

PrEP is indicated for HIV-negative individuals at high ongoing risk. The standard regimen is daily tenofovir DF plus emtricitabine. When taken consistently, it reduces transmission risk by more than ninety-nine per cent. It has been available on the NHS since 2020. An event-driven option exists for men who have sex with men: two tablets two to twenty-four hours before sex, one tablet twenty-four hours after, and one tablet forty-eight hours after. This schedule is not recommended for receptive anal sex or for patients with hepatitis B.

Oliver Hart

Three things must be monitored during PrEP. Renal function must be checked at baseline and every three months, because tenofovir is nephrotoxic. HIV testing must be done every three months — if someone acquires HIV whilst on PrEP, continuing PrEP alone would be inadequate and could cause resistance. And hepatitis B status must be checked before starting. Tenofovir is active against hepatitis B, so stopping PrEP abruptly in a hepatitis B co-infected patient can trigger a hepatitis flare — sometimes severe.

Alys Davies

Remember. PEP must be started within 72 hours of HIV exposure, this window is absolute. After 72 hours, PEP is not indicated and should not be prescribed.

Oliver Hart

Let’s move on to our rapid-recall.

Alys Davies

This section is all about what you know, and quickly!

Oliver Hart

We’ll ask you a question, give you a couple of seconds to answer, then give you the correct answer. Just try to shout out your answer in time!

Alys Davies

Question one: What is the third drug, letter P, in the mnemonic RIPE?

Oliver Hart

The answer is Pyrazinamide

Alys Davies

Question two: Which drug in mnemonic RIPE causes optic neuritis, and what must be checked before prescribing it?

Oliver Hart

The answer is Ethambutol. Before prescribing it, you should check visual acuity and colour vision and monitor it throughout treatment.

Alys Davies

Question three: A patient has PCP prophylaxis with a CD4 count as below 200 cells per microlitre, what drug should they be started?

Oliver Hart

Co-trimoxazole should be started.

Alys Davies

Question four: In EBV, what happens if you give amoxicillin?

Oliver Hart

When you give amoxicillin, a maculopapular rash could develop. This is only true for 90% of patients.

Alys Davies

Question five: Which malaria species is most dangerous, and why?

Oliver Hart

Plasmodium falciparum is most dangerous because it can cause cerebral malaria, severe anaemia, and multiorgan failure. It also has the highest mortality.

Alys Davies

Question six: What is first-line treatment for severe malaria?

Oliver Hart

IV artesunate is the recommended treatment. Quinine is used only if artesunate is unavailable.

Alys Davies

Question seven: In the first week of enteric fever, which investigation is most sensitive?

Oliver Hart

The answer is blood cultures because there can be a positive result in approximately eighty per cent of cases in week one.

Alys Davies

Question eight: What ferritin level is highly suggestive of adult-onset Still's disease?

Oliver Hart

The answer is ten thousand micrograms per litre or greater.

Alys Davies

Question nine: What is first-line treatment for gonorrhoea?

Oliver Hart

The answer is ceftriaxone, one gram intramuscularly as a single dose.

Alys Davies

And finally, Question ten: What is the maximum time window for starting PEP after HIV exposure?

Oliver Hart

The answer is seventy-two hours. After that, it is not indicated.

Alys Davies

That is your Infectious Disease rapid recall done.

Oliver Hart

Thank you for joining us for this episode.

Alys Davies

If you have any questions or would like to recap any of the topics we have gone through today, take a moment to look back over the module.

Oliver Hart

We will see you in the next episode. Bye!