Infectious Diseases
Browse 117 topics in infectious diseases.
Acute Bronchiolitis - Adult
Acute bronchiolitis in adults is an inflammatory condition of the small airways (bronchioles, below 2 mm diameter) most ... ACEM Primary Written, ACEM Primary V
Acute Diarrhoea and Gastroenteritis
Acute diarrhoea is defined as the passage of three or more loose or watery stools per day (or more frequent than normal for the individual) lasting less than 14 days . It is a leading cause of outpatient visits and...
Acute Hepatitis
The majority of cases are self-limiting; however, a small percentage can progress to Acute Liver Failure (ALF) , defined by the development of coagulopathy (INR ≥1.5) and encephalopathy. Management is primarily...
Acute HIV Infection & Seroconversion
Acute HIV infection, also known as Primary HIV Infection or Acute Retroviral Syndrome (ARS), represents the period immediately following HIV acquisition until the development of a stable "viral set point." It...
Acute Osteomyelitis (Paediatric)
Acute Haematogenous Osteomyelitis (AHO) is a bacterial infection of the bone marrow, primarily affecting the rapidly growing metaphyses of long bones in children. It represents one of the most important paediatric...
Acute Rheumatic Fever
Key Facts Definition : Post-infectious inflammatory syndrome following Group A streptococcal pharyngitis, affecting heart, joints, brain, and skin Global Incidence : 8-51 per 100,000 in developing countries; 1-3 per...
Acute Sepsis - Paediatric
Sepsis in children is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection.... MRCPCH exam preparation.
Acute Soft Tissue Infection
Acute soft tissue infections (SSTIs) represent a spectrum of bacterial infections affecting the skin, subcutaneous tissu... MRCS exam preparation.
African Trypanosomiasis (Sleeping Sickness)
Human African Trypanosomiasis (HAT), commonly known as sleeping sickness, is a vector-borne parasitic disease caused by ... MRCP exam preparation.
Amoebiasis (Amoebic Dysentery)
Amoebiasis is a parasitic infection caused by the protozoan Entamoeba histolytica, transmitted via the faecal-oral route... MRCP exam preparation.
Anthrax
Bacillus anthracis is classified as a Category A bioterrorism agent by the CDC due to its stability as spores (surviving decades in soil), ease of dissemination, high mortality potential, and capacity to cause public...
Aplastic Crisis
The condition is most commonly triggered by parvovirus B19 infection, which selectively targets erythroid precursors via P antigen (globoside) receptor binding, causing direct cytotoxic lysis and arrest of red cell...
Bacterial Meningitis
Clinical Significance : Annual incidence is 1-2 per 100,000 in developed countries. Streptococcus pneumoniae (pneumococcus) is the most common cause in adults (60%). Early recognition and empirical antibiotics within...
Bacterial Meningitis - Adult
Bacterial meningitis is a life-threatening infection of the meninges requiring immediate empirical antibiotics (Ceftriax... ACEM Fellowship Written, ACEM Fellow
Bacterial Meningitis - Paediatric
Never delay antibiotics for lumbar puncture - Draw blood cultures, give antibiotics, then perform LP if safe... ACEM Primary Written, ACEM Primary Viva exam
Bacterial Vaginosis
While not strictly classified as a Sexually Transmitted Infection (STI), BV is sexually associated, with increased prevalence among women with new or multiple sexual partners, and particularly high concordance among...
Botulism
Botulism is a rare but potentially life-threatening neuroparalytic illness caused by botulinum toxin, produced by the an... MRCP, USMLE exam preparation.
Brucellosis (Malta Fever)
Brucellosis is a systemic zoonotic infection caused by Brucella species, small Gram-negative, facultatively intracellula... MRCP exam preparation.
Cellulitis and Erysipelas
Cellulitis is a common, spreading bacterial infection of the deep dermis and subcutaneous tissue, typically presenting with localised heat, redness (erythema), swelling (oedema), and pain. Erysipelas is a superficial...
Chagas Disease (American Trypanosomiasis)
Chagas disease is a potentially life-threatening systemic parasitic infection caused by the protozoan hemoflagellate Try... MRCP exam preparation.
Chickenpox (Varicella)
Chickenpox (varicella) is a highly contagious primary infection caused by varicella-zoster virus (VZV), a member of the ... MRCPCH, RCPCH Progress Test exam pre
Chlamydia trachomatis Infections
Chlamydia trachomatis is an obligate intracellular Gram-negative bacterium that causes the most prevalent bacterial sexu... MRCP exam preparation.
Cholera
The cornerstone of cholera management is rapid and aggressive fluid replacement with oral rehydration solution (ORS) or intravenous fluids. With appropriate rehydration therapy, case fatality rates can be reduced from...
Chronic Fatigue Syndrome (ME/CFS)
Comprehensive evidence-based guide to myalgic encephalomyelitis/chronic fatigue syndrome diagnosis and management including IOM/CDC criteria, post-exertional malaise, severity classification, and energy management...
Clostridioides difficile Infection (CDI)
The clinical spectrum of CDI ranges from mild, self-limiting diarrhoea to life-threatening pseudomembranous colitis, tox... MRCP exam preparation.
Clostridioides difficile Infection (CDI)
"Stop Unnecessary Antibiotics" : First and most important step. Discontinue the inciting antibiotic and any other unnecessary antibiotics immediately.
Community Acquired Pneumonia
Community Acquired Pneumonia (CAP) is an acute infection of the lung parenchyma acquired outside of the hospital setting... MRCP, USMLE exam preparation.
Community-Acquired Pneumonia - Adult
Community-acquired pneumonia (CAP) is an acute lower respiratory tract infection acquired outside hospital, presenting w... ACEM Fellowship Written, ACEM Fellow
Community-Acquired Pneumonia (CAP)
Successful management is predicated on the "Early Recognition and Rapid Intervention" paradigm. This involves immediate clinical suspicion, prompt severity stratification using validated scoring systems (CURB-65 or...
COVID-19
COVID-19 (Coronavirus Disease 2019) is a systemic viral illness caused by the novel coronavirus SARS-CoV-2 (Severe Acute... MRCP, USMLE exam preparation.
Cryptococcosis
Cryptococcosis is a potentially life-threatening systemic fungal infection caused by encapsulated yeasts of the Cryptoco... MRCP exam preparation.
Cytomegalovirus (CMV) Infection
Cytomegalovirus (CMV), also known as Human Herpesvirus 5 (HHV-5) , is a ubiquitous β-herpesvirus that establishes lifelong latent infection after primary exposure. CMV infection represents a critical spectrum of...
Dengue Fever
Dengue fever is the most prevalent mosquito-borne viral infection worldwide, caused by the dengue virus (DENV), a single... MRCP exam preparation.
Diphtheria
The diphtheria exotoxin is absorbed systemically and causes serious complications including myocarditis (Heart failure, Arrhythmias, Complete Heart Block) and neuropathy (Cranial nerve and peripheral nerve paralysis)....
Discitis & Vertebral Osteomyelitis
Discitis (also termed spondylodiscitis or vertebral osteomyelitis) represents an infection of the intervertebral disc space and adjacent vertebral bodies. This condition constitutes a diagnostic and therapeutic...
Dog & Human Bites
Mammalian bites (Dog, Cat, Human) are common injuries with significant infection risk due to inoculation of polymicrobial oral flora deep into tissues. Dog bites account for 60-90% of mammalian bite injuries...
Eczema Herpeticum
Key Facts Aetiology : HSV-1 (85-90% of cases) or HSV-2 infection on disrupted skin barrier Risk population : Predominantly atopic dermatitis patients (especially moderate-to-severe, childhood-onset disease) Incidence...
Erysipelas
Primary Pathogen : Group A Streptococcus ( Strep pyogenes ) - 80-90% of cases Secondary Pathogens : Group G/C Streptococcus ( S. dysgalactiae ) - increasingly recognized Anatomical Depth : Upper dermis and superficial...
Genital Herpes (HSV)
Genital herpes is a chronic, lifelong sexually transmitted infection caused by herpes simplex virus type 1 (HSV-1) or type 2 (HSV-2). It is characterized by painful genital ulceration during primary and recurrent...
Gentamicin Prescribing in Adults
Gentamicin is a bactericidal aminoglycoside antibiotic with potent activity against aerobic Gram-negative bacteria, including Pseudomonas aeruginosa . It is characterized by:
Giardiasis
Transmission occurs primarily via the fecal-oral route through ingestion of infectious cysts in contaminated water, food, or via person-to-person contact. The infection is particularly prevalent among travelers to...
Gonorrhoea
The organism is an obligate human pathogen that primarily infects mucosal surfaces lined by columnar or cuboidal epithelium: Urethra, Endocervix, Rectum, Pharynx, and Conjunctiva . Stratified squamous epithelium...
Group B Streptococcus in Pregnancy
Group B Streptococcus (GBS, Streptococcus agalactiae ) is a gram-positive, β-hemolytic bacterium that colonizes the gastrointestinal and genitourinary tracts of approximately 18-20% of pregnant women worldwide. While...
Haemolytic Uraemic Syndrome (HUS)
Haemolytic Uraemic Syndrome (HUS) is a thrombotic microangiopathy (TMA) characterized by the classic triad of:... MRCPCH exam preparation.
Helicobacter Pylori
Key Facts Global Prevalence : 4.4 billion people infected worldwide (58% of global population), with marked geographic variation (20-30% in developed nations, 70-90% in developing countries). Discovery : Nobel Prize...
Hepatitis A
The disease demonstrates significant geographic variation in endemicity, with high prevalence in regions with poor sanitation and hygiene infrastructure. In developed countries, most cases are imported through...
Hepatitis B (Adult)
Hepatitis B virus (HBV) is a partially double-stranded DNA hepatotropic virus of the Hepadnaviridae family that causes both acute and chronic liver disease. Unlike other hepatitis viruses, HBV establishes a persistent...
Hepatitis C
Transmission occurs predominantly via parenteral exposure : injection drug use (IVDU), blood transfusions prior to universal screening (pre-1992 in the UK, pre-1990 in the USA), needlestick injuries, vertical...
Herpes Zoster (Shingles)
Herpes zoster (shingles) results from reactivation of latent varicella zoster virus (VZV) from dorsal root, cranial nerv... MRCP, PLAB exam preparation.
HIV & AIDS
Human Immunodeficiency Virus (HIV) is a lentivirus belonging to the Retroviridae family that selectively infects and dep... MRCP exam preparation.
HIV Infection (Adult)
Human Immunodeficiency Virus (HIV) is a lentivirus (subfamily of retroviruses) that targets the human immune system, specifically CD4+ T-lymphocytes (helper T cells), macrophages, and dendritic cells. Progressive...
Hospital-Acquired Pneumonia
Hospital-acquired pneumonia (HAP) is pneumonia that develops ≥48 hours after hospital admission and was not incubating a... MRCP exam preparation.
Hospital-Acquired Pneumonia and Ventilator-Associated Pneumonia
Hospital-acquired pneumonia (HAP) is defined as pneumonia that develops 48 hours or more after hospital admission and wa... MRCP, FFICM exam preparation.
Human Papillomavirus (HPV) Infection
Human Papillomavirus (HPV) is a double-stranded DNA virus of the Papillomaviridae family, representing the most common sexually transmitted infection (STI) worldwide . Over 200 HPV genotypes have been identified, with...
Hydatid Disease (Echinococcosis)
Humans are accidental intermediate hosts, infected through ingestion of parasite eggs from contaminated food or contact with definitive hosts (primarily dogs). The larvae migrate to the liver (60-70%) or lungs...
Immune Dysfunction Pathology in Critical Illness
Immune dysfunction in critical illness encompasses both hyperinflammation (SIRS) and immunosuppression (CARS/immunoparalysis). The initial pro-inflammatory response involves PAMP/DAMP recognition, cytokine release...
Infectious Mononucleosis
Key Facts Causative Agent : Epstein-Barr virus (EBV/HHV-4), a double-stranded DNA gamma-herpesvirus. Incidence : 45-50 per 100,000 population annually in Western countries; peaks in adolescents aged 15-24. Incubation...
Infective Gastroenteritis
While the majority of adult cases in developed nations are viral (Norovirus) and self-limiting, bacterial gastroenteritis ( Campylobacter , Salmonella , E. coli ) presents a more severe clinical picture, often with...
Invasive Aspergillosis
Invasive Aspergillosis (IA) is a life-threatening opportunistic fungal infection caused predominantly by Aspergillus fum... MRCP exam preparation.
Invasive Candidiasis
Risk factors are ubiquitous in intensive care: broad-spectrum antibiotics, central venous catheters (CVCs), Total Parenteral Nutrition (TPN), abdominal surgery, neutropenia, immunosuppression, renal replacement...
Japanese Encephalitis
A comprehensive gold-standard guide to Japanese Encephalitis, covering the Culex mosquito vector, classic thalamic MRI changes, CSF findings, vaccination protocols, supportive care, and neurological sequelae.
Legionnaires' Disease
The disease represents 2-9% of community-acquired pneumonia (CAP) cases but accounts for a disproportionately high number of severe pneumonia cases requiring ICU admission. Mortality ranges from 5-10% in...
Leishmaniasis
Comprehensive evidence-based guide to Leishmaniasis covering all three clinical forms (Cutaneous, Mucocutaneous, Visceral), epidemiology, pathophysiology, diagnosis, and management strategies with emphasis on liposomal...
Leptospirosis (Weil's Disease)
Leptospirosis is a spirochaetal zoonosis of global significance, representing the most common zoonotic infection worldwi... MRCP exam preparation.
Lung Abscess
Lung abscess is a circumscribed collection of pus within the lung parenchyma resulting from suppurative necrosis and cav... MRCP exam preparation.
Lyme Disease
A comprehensive evidence-based guide to Lyme Disease covering epidemiology, pathophysiology, the two-tier diagnostic testing protocol, stage-based management with antibiotic regimens, and complications including...
Lymphadenopathy
The generalist's challenge is to filter the "benign majority" from the "malignant minority". While less than 1% of primary care patients with lymphadenopathy have malignancy, this rises to 40-60% in specialist...
Measles
Clinical Pearls: One of the most contagious diseases known (R0 = 12-18) Koplik spots appear 1-2 days before rash, pathognomonic Rash starts behind ears, spreads cephalocaudally Vitamin A supplementation reduces...
Meningitis and Encephalitis in Adults
Meningitis and encephalitis are life-threatening infections of the central nervous system requiring immediate recognition and treatment. Bacterial meningitis is inflammation of the meninges caused predominantly by...
Mucormycosis
A comprehensive guide to Mucormycosis, covering epidemiology, molecular pathophysiology of angioinvasion, clinical manifestations across all forms (rhinocerebral, pulmonary, disseminated, cutaneous), diagnostic...
Mumps (Child)
Mumps is an acute, highly contagious viral infection caused by the Mumps virus (genus Rubulavirus , family Paramyxoviridae ), characterised clinically by painful, bilateral parotid gland swelling (epidemic parotitis)....
Mycoplasma Pneumonia (Atypical Pneumonia)
Mycoplasma pneumoniae is a cell wall-deficient bacterium representing one of the smallest free-living organisms capable of self-replication. It is the most common cause of atypical pneumonia in children and young...
Myocarditis
The diagnosis requires high clinical suspicion, particularly in young patients presenting with cardiac symptoms following viral illness. Cardiac magnetic resonance imaging (CMR) has emerged as the gold standard...
Necrotising Fasciitis
The hallmark clinical feature is severe pain that appears disproportionate to the physical examination findings—a result of deep fascial involvement and nerve ischaemia occurring before significant skin changes become...
Neonatal Sepsis
Key Facts Global Incidence : EOS affects 0.5-1.0 per 1000 live births in term infants; 10-20 per 1000 in preterm infants Mortality : Overall 10-20%; up to 50% in very low birth weight (VLBW) infants (less than 1500g)...
Oral Candidiasis (Adult)
Oral candidiasis, commonly known as oral thrush, is a fungal infection of the oral mucosa caused predominantly by Candid... MRCP exam preparation.
Pandemic Response in Intensive Care
Activate Hospital Incident Command System (HICS)... CICM Second Part Written, CICM Second Part Hot Case exam preparation.
Pediatric Bacterial Meningitis
Comprehensive evidence-based guide to diagnosis and management of bacterial meningitis in neonates, infants, and children - emergency recognition, age-specific pathogens, CSF interpretation, empiric antibiotics, and...
Pneumocystis Pneumonia (PCP)
Pneumocystis Pneumonia (PCP), caused by the fungus Pneumocystis jirovecii, is a life-threatening opportunistic infection... MRCP exam preparation.
Pneumonia - Adult
CURB-65 score (0-1: outpatient, 2: consider admission, ≥3: severe - ICU assessment) is the most validated severity to... ACEM Fellowship Written, ACEM Fellow
Pneumonia - Paediatric
Tachypnoea is the most sensitive clinical sign of pneumonia: greater than 60/min (below 2 months), greater than 50/mi... ACEM Fellowship Written, ACEM Fellow
Poliomyelitis (Child)
Poliomyelitis (polio) is an acute viral infection caused by poliovirus , a human enterovirus belonging to the Picornaviridae family. While the majority of poliovirus infections are asymptomatic or cause only minor...
Postpartum Endometritis
The condition is characterised by the classic triad : fever ( 38°C), uterine tenderness, and offensive lochia. Caesarean section is the single most important risk factor, increasing the risk 10-20 fold compared to...
Progressive Multifocal Leukoencephalopathy (PML)
A comprehensive guide to Progressive Multifocal Leukoencephalopathy (PML), covering JC Virus pathophysiology, risk stratification with Natalizumab, diagnostic criteria, MRI features including subcortical U-fibre...
Prostatitis
Type I (Acute Bacterial Prostatitis) is a urological emergency characterised by acute systemic infection with fever, rigors, and an exquisitely tender prostate. This represents approximately 5-10% of cases and...
Q Fever
Acute Q fever presents in a spectrum from asymptomatic infection (60%) to three main clinical syndromes: flu-like illness , atypical pneumonia , and granulomatous hepatitis . Most acute cases are self-limiting, but...
Rabies
Key Facts Causative Agent : Lyssavirus genus (14 species); rabies virus (genotype 1) causes 95% of human cases Transmission : Primarily via bite from rabid animal; saliva contact with broken skin or mucous membranes;...
Reactive Arthritis (Adult)
Reactive arthritis (ReA) is a sterile inflammatory arthritis that develops following an infection at a distant site, typically gastrointestinal or genitourinary . It is classified as one of the seronegative...
Rheumatic Fever
Acute Rheumatic Fever (ARF) is a delayed, non-suppurative, autoimmune sequela of Group A Streptococcus (GAS) pharyngitis. It represents a multisystem inflammatory disorder characterized by migratory polyarthritis,...
Roseola Infantum
HHV-6 seroprevalence reaches 95% by age 2-3 years in most populations worldwide, establishing roseola as a near-universal childhood infection with lifelong viral latency following primary infection. The infection is...
Rubella (German Measles)
Rubella, also known as German measles, is an acute viral infection caused by the rubella virus , a single-stranded RNA virus of the Togaviridae family. The clinical significance of rubella exists on two distinct...
Scabies
Nocturnal Itch Pearl : The characteristic nocturnal pruritus occurs because mites are more active in warm environments. Night-time scratching + web space involvement = think scabies.
Schistosomiasis (Bilharzia)
Schistosomiasis is a chronic parasitic disease caused by blood flukes (trematodes) of the genus Schistosoma . It ranks as the second most devastating parasitic disease globally after malaria, affecting over 240...
Septic Arthritis
The classic presentation is a short history (less than 1 week) of a single hot, swollen, painful joint with restricted range of movement and systemic upset. Inability to weight bear is a key sign.
Severe Sepsis - Adult
Sepsis-3 Definition: Organ dysfunction (SOFA score increase ≥2) caused by infection - SIRS criteria abandoned... ACEM Primary Written, ACEM Primary Viva exam
Shigellosis (Bacillary Dysentery)
Shigellosis is an acute invasive bacterial colitis caused by species of the genus Shigella , manifesting as inflammatory diarrhoea with blood and mucus (dysentery). Distinguished by an extraordinarily low infectious...
SIRS and Sepsis Pathology
Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. The pathophysiology involves recognition of PAMPs and DAMPs by pattern recognition receptors (TLRs), triggering a...
Slapped Cheek Syndrome (Fifth Disease/Parvovirus B19)
Slapped Cheek Syndrome (Erythema Infectiosum), historically termed "Fifth Disease" as the fifth described childhood exanthem, is a common viral infection caused by Human Parvovirus B19 (B19V). This small,...
Soil Transmitted Helminths
A comprehensive, evidence-based guide to the 'Big Three' Soil Transmitted Helminths (Ascaris, Trichuris, Hookworm). Covers detailed life cycles, Loeffler's syndrome, Th2 immunology, Mass Drug Administration (MDA)...
Splenomegaly
The spleen's unique anatomical position in the portal circulation and its role as a reticuloendothelial filter make it susceptible to enlargement via three primary mechanisms: congestion (e.g., cirrhosis),...
Staphylococcal Scalded Skin Syndrome
Staphylococcal Scalded Skin Syndrome (SSSS) is an acute toxin-mediated exfoliative dermatosis caused by epidermolytic ex... MRCPCH, DCH exam preparation.
Surgical Site Infection in Adults
Surgical site infection (SSI) remains the most common healthcare-associated infection (HAI) in surgical patients, accounting for nearly 20% of all HAIs. Defined by the Centers for Disease Control and Prevention (CDC)...
Tetanus
The global burden of tetanus has decreased dramatically over the past three decades, with deaths falling by nearly 90% between 1990 and 2019, primarily due to the WHO's Maternal and Neonatal Tetanus Elimination...
Tinea Infections
The three principal genera of dermatophytes are Trichophyton , Microsporum , and Epidermophyton . Trichophyton rubrum accounts for 60-80% of all dermatophyte infections globally and is the most common cause of chronic...
Tinea Infections (Dermatophytosis)
Dermatophytosis (tinea infections) represents a group of superficial mycoses caused by keratinophilic fungi of the genera Trichophyton , Microsporum , and Epidermophyton . These organisms infect keratinized...
Toxoplasmosis
The parasite's complex life cycle involves cats as the definitive host, with humans and other warm-blooded animals serving as intermediate hosts. Transmission occurs through ingestion of oocysts from cat feces,...
Tuberculosis (Adult)
Tuberculosis (TB) is a chronic granulomatous infectious disease caused by organisms of the Mycobacterium tuberculosis co... MRCP exam preparation.
Tuberculosis (Pulmonary) - Adult
TB affects primarily the lung parenchyma but has the biological capacity to disseminate to virtually every organ system ... MRCP, Respiratory Medicine exam prep
Typhoid and Paratyphoid Fever (Enteric Fever)
Enteric fever is a life-threatening systemic infection caused by the invasive bacteria Salmonella enterica serovar Typhi (typhoid fever) or Paratyphi A, B, C (paratyphoid fever). This condition remains a major global...
Urinary Tract Infection (Adult)
Urinary tract infection (UTI) represents one of the most prevalent bacterial infections worldwide, accounting for approximately 150 million cases annually and significant healthcare expenditure. UTIs are classified...
Urinary Tract Infection in Adults
Urinary tract infection (UTI) is bacterial infection of any component of the urinary system, most commonly the bladder (... MRCP exam preparation.
Urosepsis
Key Facts Definition : Sepsis (life-threatening organ dysfunction) arising from urinary tract source Incidence : Most common source of community-acquired sepsis in patients >65 years Mortality : 10-15% overall;...
Varicella Zoster Virus (Chickenpox & Shingles)
Varicella Zoster Virus (VZV), also known as Human Herpesvirus 3 (HHV-3), is a neurotropic alphaherpesvirus that causes two clinically distinct syndromes separated by decades: varicella (chickenpox) as the primary...
Viral Encephalitis
Herpes Simplex Virus Type 1 (HSV-1) is the most common identified cause of sporadic, severe viral encephalitis in developed countries, accounting for 10-20% of all cases. Without treatment, HSV encephalitis carries a...
Viral Haemorrhagic Fevers
VHFs are classified as high-consequence infectious diseases (HCID) due to their high case-fatality rates (ranging from 1% to 90% depending on the pathogen), potential for person-to-person transmission, limited...
Yellow Fever
The clinical spectrum ranges from asymptomatic or mild febrile illness in approximately 85% of cases to severe disease characterised by hepatorenal failure, haemorrhage, and shock in 15% of infected individuals. The...
Zika Virus Infection
Zika virus (ZIKV) is a mosquito-borne Flavivirus that emerged from relative obscurity to become a major public health concern following massive outbreaks in the Americas from 2015-2016. While Zika virus infection...