Infectious Disease

Candidiasis is infection by Candida yeasts, usually a superficial mucocutaneous infection but occasionally invasive candidaemia; the key clinical task is to distinguish symptomatic disease from colonisation and match treatment to site, host, species, susceptibility and pregnancy status.

An acute bacterial infection of the dermis and subcutaneous tissue causing spreading inflammation; the essential clinical task is to distinguish uncomplicated cellulitis from sepsis, orbital disease, abscess and necrotising fasciitis.

Antibiotic-associated, toxin-mediated colitis in which loss of gut colonisation resistance permits C. difficile to proliferate, causing diarrhoea that may progress to ileus, toxic megacolon and perforation.

COVID-19 is illness caused by SARS-CoV-2, ranging from a self-limiting respiratory infection to hypoxic pneumonia and multi-organ complications; management depends on severity, oxygen requirement, risk of progression, timing, comorbidity and current UK treatment pathways.

Herpes simplex virus causes recurrent painful mucocutaneous lesions and can also cause sight-threatening keratitis, encephalitis, eczema herpeticum, neonatal disease and disseminated infection; management depends on site, severity, host, pregnancy and timing.

A chronic retroviral infection that progressively impairs CD4-mediated immunity, but is now usually controllable with antiretroviral therapy that protects health and prevents sexual transmission when viral suppression is sustained.

Acute infectious diarrhoea with or without vomiting, managed by prioritising hydration and sepsis assessment, testing selectively, avoiding harmful antibiotics in STEC, and controlling transmission and public-health risk.

Infectious mononucleosis is usually primary Epstein–Barr virus infection causing fever, exudative pharyngitis, lymphadenopathy and marked fatigue; the high-yield safety issues are avoiding unnecessary aminopenicillins, protecting an enlarged spleen and recognising airway, abdominal, hepatic, neurological and haematological complications.

An acute respiratory viral infection whose rapid antigenic change allows it to repeatedly evade population immunity, producing seasonal epidemics and occasional pandemics.

Lyme disease is a multisystem infection caused by Borrelia species and transmitted by Ixodes ticks; diagnose erythema migrans clinically, use accredited serology for presentations without the rash, and escalate focal neurological, cardiac, ocular, joint, pregnancy and paediatric disease through the current NICE pathway.

A mosquito-borne Plasmodium infection in which travel history, species and severity determine how quickly treatment must begin.

Bacteria reaching the subarachnoid space provoke an inflammatory response that raises intracranial pressure and injures cranial nerves, while meningococcal bloodstream invasion adds purpura, coagulopathy and shock.

Sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection, in which inflammatory signalling and microvascular failure injure organs remote from the infected site.

Shingles is reactivation of latent varicella-zoster virus in a sensory ganglion, usually causing a painful unilateral dermatomal rash; treat eligible patients promptly, recognise ophthalmic, neurological and disseminated disease, manage post-herpetic neuralgia, and offer current Shingrix vaccination to eligible cohorts.

Tetanus is a rare but life-threatening neurological disease caused by tetanospasmin from Clostridium tetani in a wound; recognise it clinically, give urgent hospital treatment and post-exposure prophylaxis according to the current UKHSA wound algorithm, and prevent it with the five-dose vaccine schedule.

Toxic shock syndrome is a rapidly progressive toxin-mediated illness caused by Staphylococcus aureus or group A Streptococcus, with fever, diffuse rash, hypotension and multi-organ dysfunction; treat it as an emergency with sepsis resuscitation, immediate source control and specialist antimicrobial therapy.

Toxoplasma gondii infection is usually asymptomatic or mild in immunocompetent people, but needs specialist management when it affects the eye, brain, pregnancy or fetus; keep these pathways separate.

A chronic Mycobacterium tuberculosis complex infection that may remain latent or reactivate as active pulmonary or extrapulmonary disease, requiring microbiological diagnosis, multi-drug treatment and public-health contact tracing.