Acute pharyngitis
Acute pharyngitis: why most sore throats are viral, how to spot and test for group A strep, antibiotic choice and duration, complications and red flags.
Checked against sourcesVerified 28 October 2026
Infectious disease
Infections of every system: how they present, how they are diagnosed, and how they are treated and prevented.
Introduction
Infectious disease covers illness caused by bacteria, viruses, fungi and parasites, in every organ system. The same few questions apply each time: where is the infection, which organism is likely, how sick is the patient, and which test and which drug come first.
This section starts with the infections of the airways, ears, eyes and neck, then the infections of the nervous system, HIV and the opportunistic infections that follow it, fungal disease, sexually transmitted infections, urinary and bloodstream infections, and finally the infections carried by insects, ticks and animals.
Every topic uses the same layout: a short summary, what you should be able to do afterwards, the mechanism, the clinical picture, tests, treatment and the traps. Doses, thresholds and cut-offs are checked against named guidelines and shown with their source, because guidelines, resistance patterns and countries differ.
How to study infectious disease
For each infection, learn the organism, the site, the test that proves it and the first drug in the same breath. Most exam and ward questions are one of these four links with a gap you have to fill.
Learn the emergencies as pathways: sepsis, bacterial meningitis, encephalitis, necrotising infection, infective endocarditis and neutropenic fever. Practise saying the first three actions aloud, including when to take cultures and when to give antibiotics.
Use the patient's immune state as a second axis. A low CD4 count, neutropenia, pregnancy, an implant or a recent journey each change the likely organisms, so read the special-groups section of every topic.
Infectious disease links to every other system, so follow the related links. Content here is for study and does not replace local protocols, local resistance data or a senior clinician's judgement.
Contents by part
The topics below are in teaching order. Each part builds on the one before it.
- Respiratory and head and neck infections. Start with the upper airway, ears, eyes and neck, then influenza and pneumonia, and finish with tuberculosis.
- Central nervous system infections. Meningitis, encephalitis and abscess, then the toxin disease botulism.
- HIV and the opportunistic infections. HIV first, then the infections that appear as the CD4 count falls.
- Fungal infections. The endemic fungi, then aspergillosis.
- Sexually transmitted infections. Urethritis and cervicitis, gonorrhoea, syphilis and the approach to genital ulcers.
- Urinary and bloodstream infections. Urinary infection, then sepsis, endocarditis and fever in the neutropenic patient.
- Vector-borne and zoonotic infections. Malaria, the mosquito-borne viruses, tick-borne disease and anthrax.
- Bone and viral illness. Osteomyelitis and infectious mononucleosis.
- Enteric and tropical infections. Gut, tropical and neglected infections, from cholera and typhoid to parasites and leprosy.
- Cholera
- Typhoid and enteric fever
- Amoebiasis, giardiasis and cryptosporidiosis
- Intestinal helminths, strongyloidiasis and schistosomiasis
- Leishmaniasis, trypanosomiasis and Chagas disease
- Tapeworm infections: neurocysticercosis and hydatid disease
- Lymphatic filariasis, onchocerciasis and loiasis
- Leprosy
- Trachoma and other neglected tropical diseases
- Scabies, lice and other ectoparasites
- Prevention, stewardship and travel. Preventing infection: vaccines and travel advice, hospital infection control and the responsible use of antimicrobials.
Topics
Acute sinusitis
Viral and bacterial acute sinusitis: how to tell them apart, diagnose by symptoms, treat, and avoid complications.Checked against sourcesVerified 28 October 2026Otitis externa
Acute, chronic and necrotising otitis externa: causes, symptoms, diagnosis, treatment and warning signs.Checked against sourcesVerified 28 October 2026Infectious conjunctivitis and orbital cellulitis
How to recognise, treat and prevent viral, bacterial, gonococcal, chlamydial and allergic conjunctivitis, and orbital cellulitis.Checked against sourcesVerified 28 October 2026Dacryocystitis and infectious keratitis
Acute dacryocystitis plus bacterial, herpetic, fungal and Acanthamoeba keratitis: recognition, urgent referral, and treatment.Checked against sourcesVerified 28 October 2026Oral and neck space infections
Dental abscess and periodontal infections, Vincent angina, oral herpes, Ludwig angina, acute lymphadenitis, scrofula, cat-scratch disease and parotitis.Checked against sourcesVerified 28 October 2026
Influenza
What influenza is, how it presents, its complications, how tests and antivirals help, and how it is prevented.Checked against sourcesVerified 28 October 2026Community-acquired and hospital-acquired pneumonia
Community- and hospital-acquired pneumonia: pathogens, presentation, severity scores, imaging, treatment with doses, complications and prevention.Checked against sourcesVerified 28 October 2026Tuberculosis
Airborne infection with Mycobacterium tuberculosis: why most infections stay latent, how active disease presents in lung and elsewhere, how it is diagnosed.Checked against sourcesVerified 28 October 2026COVID-19 and other respiratory viruses
COVID-19 (SARS-CoV-2 infection) and other common respiratory viruses: presentation, testing, treatment, vaccines and prevention.Checked against sourcesVerified 31 October 2026Diphtheria
Diphtheria toxin from toxigenic Corynebacterium diphtheriae forms a pseudomembrane and attacks heart, nerves and kidneys; antitoxin, antibiotics and.Checked against sourcesVerified 31 October 2026Bacterial and viral meningitis
Bacterial and viral meningitis: causes, red flags, CSF findings, empiric antibiotics, dexamethasone, chemoprophylaxis and vaccination.Checked against sourcesVerified 28 October 2026Encephalitis
Encephalitis: causes, presentations, CSF and imaging, aciclovir dosing, autoimmune treatment, prognosis and low-resource care.Checked against sourcesVerified 28 October 2026Brain abscess
A focal pus collection in the brain: sources, bugs, ring-enhancing imaging, why lumbar puncture is dangerous, and how to treat it.Checked against sourcesVerified 28 October 2026Botulism
Botulinum neurotoxin causes descending flaccid paralysis: recognition, emergency management, and public-health steps.Checked against sourcesVerified 28 October 2026Tetanus
Tetanus: how Clostridium tetani toxin causes spastic paralysis, how it is recognised, treated, prevented and vaccinated against.Checked against sourcesVerified 31 October 2026Poliomyelitis and acute flaccid paralysis
How poliovirus causes paralysis, how acute flaccid paralysis is investigated, the vaccines that prevent polio, and the global eradication programme.Checked against sourcesVerified 31 October 2026Rabies and animal bites
Rabies after animal bites: risk assessment, wound washing, PEP with vaccine and immunoglobulin, and bite infections such as Pasteurella and Capnocytophaga.Checked against sourcesVerified 31 October 2026HIV infection and AIDS
HIV and AIDS: virology, transmission, stages, diagnosis, antiretroviral therapy, opportunistic infections, and prevention.Checked against sourcesVerified 28 October 2026Pneumocystis jirovecii pneumonia
Fungal pneumonia of immunocompromised people: subacute dry cough, exertional hypoxia and ground-glass opacities; diagnosed by PCR on BAL; treated with.Checked against sourcesVerified 28 October 2026Toxoplasmosis
Toxoplasma gondii infection: usually silent, dangerous in pregnancy and the immunosuppressed; cerebral, ocular and congenital disease.Checked against sourcesVerified 28 October 2026Cryptococcal meningitis
Cryptococcal meningitis: subacute fungal meningoencephalitis in advanced HIV, its diagnosis, and treatment with amphotericin, flucytosine and fluconazole.Checked against sourcesVerified 28 October 2026Cytomegalovirus infection
CMV infection: latency, transmission, congenital CMV, mononucleosis-like illness, disease in the immunocompromised, diagnosis, treatment and low-resource care.Checked against sourcesVerified 28 October 2026Mycobacterium avium complex
Mycobacterium avium complex (MAC): disseminated disease in advanced HIV, pulmonary disease in older women and chronic lung disease, with diagnosis.Checked against sourcesVerified 28 October 2026Oropharyngeal and oesophageal candidiasis
Oral thrush and Candida oesophagitis: who is at risk, how they present, how they are diagnosed and treated, with outlines of invasive and vulvovaginal.Checked against sourcesVerified 28 October 2026HIV prevention: pre-exposure and post-exposure prophylaxis
PrEP and PEP for HIV: regimens, monitoring and dosing, testing strategy, U=U, occupational and sexual exposure, and regional differences.Checked against sourcesVerified 31 October 2026Endemic fungal infections
Three dimorphic fungi acquired from soil: how they differ in geography, tissue form, presentation, diagnosis and treatment.Checked against sourcesVerified 28 October 2026Aspergillosis
Every form of aspergillosis, for everyone who breathes in Aspergillus spores: infection in the neutropenic, allergy in asthmatics, fungus balls in old.Checked against sourcesVerified 28 October 2026Chlamydia and other urethritis and cervicitis
Chlamydia and other urethritis and cervicitis: microbiology, serovars, presentation, complications, diagnosis, treatment, neonatal infection, and.Checked against sourcesVerified 28 October 2026Gonorrhoea
Purulent urethritis, cervicitis, pharyngeal and rectal infection, DGI and neonatal conjunctivitis from Neisseria gonorrhoeae; current diagnosis and treatment.Checked against sourcesVerified 28 October 2026Syphilis
A systemic infection with Treponema pallidum that mimics many diseases; how it is staged, diagnosed with serology, and cured with penicillin.Checked against sourcesVerified 28 October 2026Genital ulcers and lesions
How to sort painful from painless genital ulcers and warts, stage the work-up, and treat first-line, including herpes in pregnancy and HPV vaccination.Checked against sourcesVerified 28 October 2026Urinary tract infection and pyelonephritis
Organisms and antimicrobial drugs in urinary tract infection and pyelonephritis: uropathogens, urine tests, treatment by group and setting, complications.Checked against sourcesVerified 28 October 2026Sepsis and septic shock
What sepsis and septic shock are, how they harm organs, and how to recognise and treat them in the first hour.Checked against sourcesVerified 28 October 2026Infective endocarditis
How valve infection starts, spreads and scars; how blood cultures and echo confirm it, and how antibiotics and surgery treat and prevent it.Checked against sourcesVerified 28 October 2026Neutropenic fever
Neutropenic fever explained: definition, likely organisms, emergency antibiotics, MASCC risk stratification, duration and prophylaxis.Checked against sourcesVerified 28 October 2026Fever of unknown origin
How to define, investigate and manage prolonged unexplained fever in adults, from the classic definition through modern stepwise evaluation.Checked against sourcesVerified 28 October 2026Toxic shock syndrome and toxin-mediated infection
Toxic shock syndrome from S. aureus and S. pyogenes: toxin-mediated shock, scarlet fever, diagnosis, and treatment.Checked against sourcesVerified 31 October 2026Malaria
Malaria caused by Plasmodium parasites: transmission, species, clinical features, severe disease, diagnosis, treatment and prevention.Checked against sourcesVerified 28 October 2026Mosquito-borne viral infections
Aedes-borne viruses compared by vector, region, features, diagnosis and care, with prevention and low-resource notes.Checked against sourcesVerified 28 October 2026Lyme disease
Lyme disease, a tick-borne Borrelia infection: stages, rash-based diagnosis, two-tier serology, and antibiotic treatment.Checked against sourcesVerified 28 October 2026Babesiosis and Rocky Mountain spotted fever
Babesiosis and Rocky Mountain spotted fever: tick-borne Babesia haemolytic anaemia and Rickettsia vasculitis, with diagnosis and treatment.Checked against sourcesVerified 28 October 2026Anthrax
Bacillus anthracis infection in all its forms: cutaneous, inhalational, gastrointestinal, and injection disease, with diagnosis, CDC-guided treatment and.Checked against sourcesVerified 28 October 2026Leptospirosis, brucellosis, plague and Q fever
Four zoonotic bacterial fevers compared: exposure, presentation, diagnosis, treatment and notification (CDC, WHO).Checked against sourcesVerified 31 October 2026Viral haemorrhagic fevers
Viral haemorrhagic fevers: Ebola, Marburg, Lassa, CCHF, yellow fever, hantavirus and Rift Valley fever, with isolation, supportive care and antivirals.Checked against sourcesVerified 31 October 2026The returning traveller with fever
A practical approach to fever in someone recently returned from abroad: triage, malaria first, geography and incubation, and the key tropical infections.Checked against sourcesVerified 31 October 2026Osteomyelitis
Osteomyelitis: how bone infection starts, how to confirm it, and how to treat acute, vertebral and diabetic foot disease.Checked against sourcesVerified 28 October 2026Infectious mononucleosis
How EBV causes mono: symptoms, tests, complications, treatment, sports safety, and low-resource care.Checked against sourcesVerified 28 October 2026Septic arthritis
Septic arthritis of native and prosthetic joints: synovial fluid diagnosis, surgical drainage, and antibiotic treatment.Checked against sourcesVerified 31 October 2026Cellulitis, abscess and necrotising soft tissue infection
How cellulitis, cutaneous abscess, erysipelas and necrotising soft tissue infection are recognised and treated, including MRSA, drainage and surgical source.Checked against sourcesVerified 31 October 2026Measles, mumps and rubella
Measles, mumps and rubella: recognition, complications, outbreak control, vaccination and congenital rubella.Checked against sourcesVerified 31 October 2026Varicella and herpes zoster
Primary varicella (chickenpox) and reactivation herpes zoster (shingles): epidemiology, features, complications, antivirals, vaccines, pregnancy and.Checked against sourcesVerified 31 October 2026Cholera
Acute watery diarrhoea caused by Vibrio cholerae: how rice-water stool dehydrates, and the rehydration, antibiotics, vaccines and outbreak control that save.Checked against sourcesVerified 31 October 2026Typhoid and enteric fever
Systemic enteric fever from Salmonella Typhi and Paratyphi: presentation, complications, diagnosis, resistance-guided treatment, vaccines, and carriers.Checked against sourcesVerified 31 October 2026Amoebiasis, giardiasis and cryptosporidiosis
Amoebiasis, giardiasis and cryptosporidiosis: diagnosis and treatment of the main intestinal protozoal infections.Checked against sourcesVerified 31 October 2026Intestinal helminths, strongyloidiasis and schistosomiasis
Intestinal helminths (roundworm, hookworm, whipworm), Strongyloides hyperinfection and schistosomiasis: presentation, diagnosis, treatment with albendazole.Checked against sourcesVerified 31 October 2026Leishmaniasis, trypanosomiasis and Chagas disease
How the three major protozoal tropical infections present, how to diagnose them and how to treat and screen for them worldwide.Checked against sourcesVerified 31 October 2026Tapeworm infections: neurocysticercosis and hydatid disease
Taenia solium, taeniasis, neurocysticercosis and cystic hydatid disease: how they present, how imaging diagnoses them, and how antiparasitic, surgical and.Checked against sourcesVerified 31 October 2026Lymphatic filariasis, onchocerciasis and loiasis
Three mosquito- and biting-insect-transmitted filarial worm infections: lymphatic filariasis (elephantiasis), onchocerciasis (river blindness) and loiasis.Checked against sourcesVerified 31 October 2026Leprosy
Leprosy (Hansen disease): a chronic infection of skin and nerves, classified from tuberculoid to lepromatous, treated with multidrug therapy.Checked against sourcesVerified 31 October 2026Trachoma and other neglected tropical diseases
Trachoma and other neglected tropical diseases: SAFE strategy, yaws, Buruli ulcer, dracunculiasis, snakebite envenoming and the WHO NTD roadmap.Checked against sourcesVerified 31 October 2026Scabies, lice and other ectoparasites
Scabies and lice: how to recognise them, how to diagnose them, how to treat them with permethrin and ivermectin, and how to control outbreaks in.Checked against sourcesVerified 31 October 2026Immunisation and travel medicine
Routine immunisation across the life course plus pre-travel advice, malaria prophylaxis, and the fever cross-check.Checked against sourcesVerified 31 October 2026Infection prevention and control in hospital
How hospitals prevent and control infection: standard and transmission-based precautions, hand hygiene, isolation, sharps safety, HAI bundles and.Checked against sourcesVerified 31 October 2026Antimicrobial resistance and stewardship
How bacteria resist antibiotics (MRSA, ESBL, CRE), how infection control limits spread, and how stewardship guides drug choice.Checked against sourcesVerified 31 October 2026