Fever: Clinical Meaning

Bronchitis

Bronchitis is inflammation of the bronchial tubes that carry air to the lungs. Acute bronchitis is usually caused by viruses and resolves in 2–3 weeks. Chronic bronchitis is a form of COPD caused by long-term irritation, often from smoking.

Pneumonia

Pneumonia is an infection that inflames the air sacs (alveoli) in one or both lungs, which may fill with fluid or pus. It can be caused by bacteria, viruses, or fungi and ranges from mild to life-threatening.

Sinusitis

Sinusitis is inflammation of the sinuses, often following a cold or allergy. It causes facial pain, nasal congestion, thick nasal discharge, and reduced sense of smell. Acute sinusitis lasts up to 4 weeks; chronic sinusitis persists over 12 weeks.

Ear Infection (Otitis Media)

Ear infections occur when bacteria or viruses infect the middle ear, causing pain, fluid buildup, and temporary hearing loss. They are especially common in children but can affect adults as well.

Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease that causes inflammation in the joints, leading to pain, swelling, and eventual joint damage. Unlike osteoarthritis, RA is systemic and can affect organs including the heart and lungs.

Gout

Gout is a form of inflammatory arthritis caused by elevated uric acid levels (hyperuricemia) that form crystals in joints. It causes sudden, severe attacks of pain, swelling, redness, and tenderness, most often in the big toe.

Pancreatitis

Pancreatitis is inflammation of the pancreas, which can be acute (sudden) or chronic (long-term). Gallstones and heavy alcohol use are the most common causes. It causes severe upper abdominal pain that may radiate to the back, nausea, and vomiting.

Cholecystitis

Cholecystitis is inflammation of the gallbladder, usually caused by gallstones blocking the bile duct. It causes severe pain in the upper right abdomen, nausea, vomiting, and fever. Acute cholecystitis often requires surgery.

Cystitis (Urinary Tract Infection)

Cystitis is inflammation of the bladder, usually caused by a bacterial urinary tract infection (UTI). It causes a burning sensation during urination, frequent urge to urinate, cloudy urine, and pelvic discomfort. Women are significantly more affected than men.

Prostatitis

Prostatitis is inflammation of the prostate gland, which can be caused by bacterial infection or other factors. It causes pelvic pain, difficult or painful urination, and sometimes fever and chills. Chronic prostatitis is the most common form.

Influenza (Flu)

Influenza is a highly contagious respiratory viral illness caused by influenza A or B viruses. It spreads through respiratory droplets and causes sudden fever, severe body aches, fatigue, cough, and headache. Annual vaccination is recommended for prevention.

COVID-19

COVID-19 is an infectious respiratory disease caused by the SARS-CoV-2 virus. Symptoms range from mild (fever, cough, fatigue) to severe (pneumonia, respiratory failure). Long COVID affects some patients with persistent symptoms lasting months.

Chickenpox (Varicella)

Chickenpox is a highly contagious viral infection caused by the varicella-zoster virus. It causes an itchy blister-like rash, fever, and fatigue. It primarily affects children but can be more severe in adults. Vaccination is available.

Measles

Measles is a highly contagious viral disease characterized by fever, cough, runny nose, red eyes, and a distinctive red blotchy rash. It can cause serious complications including pneumonia and encephalitis. MMR vaccination provides effective protection.

Rubella (German Measles)

Rubella is a contagious viral infection known for its distinctive red rash. While usually mild in children, it is dangerous during pregnancy and can cause congenital rubella syndrome in the developing fetus. MMR vaccination provides effective prevention.

Whooping Cough (Pertussis)

Whooping cough is a highly contagious bacterial respiratory infection caused by Bordetella pertussis. It causes severe coughing fits followed by a high-pitched 'whoop' sound during breathing. It is most dangerous in infants. DTaP vaccination provides protection.

Kidney Cancer (Renal Cell Carcinoma)

Renal cell carcinoma is the most common kidney cancer in adults, often discovered incidentally on imaging. Symptoms include hematuria, flank pain, and a palpable mass; smoking and obesity are key risk factors.

Leukemia

Leukemia is a cancer of blood-forming tissues that disrupts normal blood cell production. It is classified by speed of progression (acute/chronic) and cell type (lymphocytic/myeloid), causing fatigue, bleeding, and infections.

Non-Hodgkin Lymphoma

Non-Hodgkin lymphoma is a group of blood cancers affecting the lymphatic system, presenting with painless swollen lymph nodes, fatigue, night sweats, and weight loss. It is more common than Hodgkin lymphoma.

Hodgkin Lymphoma

Hodgkin lymphoma is a type of lymphoma characterized by the presence of Reed-Sternberg cells. It typically affects young adults and is one of the most curable cancers with modern chemotherapy and radiation.

Bone Cancer (Osteosarcoma)

Osteosarcoma is the most common primary bone cancer, predominantly affecting adolescents. It presents as bone pain and swelling, most often around the knee; treatment involves surgery and chemotherapy.

Infective Endocarditis

Infective endocarditis is an infection of the heart valve lining by bacteria (usually Streptococcus or Staphylococcus), causing fever, heart murmur, and embolic complications. IV drug use and dental procedures are key risk factors.

Pericarditis

Pericarditis is inflammation of the pericardium (the sac surrounding the heart), causing sharp, pleuritic chest pain that improves when leaning forward. Viral infections are the most common cause; NSAIDs are the primary treatment.

Meningitis

Meningitis is inflammation of the meninges (membranes surrounding the brain and spinal cord), caused by bacteria, viruses, or fungi. Bacterial meningitis is a medical emergency causing severe headache, neck stiffness, fever, and potentially fatal if untreated.

Encephalitis

Encephalitis is inflammation of the brain parenchyma, most commonly caused by viral infections (herpes simplex, enteroviruses). It presents with fever, altered consciousness, seizures, and focal neurological deficits; early antiviral treatment is crucial.

Tuberculosis (TB)

Tuberculosis is an infectious disease caused by Mycobacterium tuberculosis, primarily affecting the lungs with symptoms of chronic cough, night sweats, fever, and weight loss. Drug-resistant TB is a growing global health threat requiring prolonged combination antibiotic therapy.

Malaria

Malaria is a life-threatening parasitic disease transmitted by Anopheles mosquitoes, causing cyclical fever, chills, and anemia. Plasmodium falciparum causes the most severe form; artemisinin-based combination therapy is the first-line treatment.

Dengue Fever

Dengue fever is a mosquito-borne viral infection causing high fever, severe headache, muscle and joint pain, and a characteristic skin rash. Dengue hemorrhagic fever is a severe form with bleeding and organ impairment.

Typhoid Fever

Typhoid fever is caused by Salmonella typhi, transmitted through contaminated food and water, causing sustained fever, abdominal pain, and rose spots. Antibiotic treatment is effective; vaccination is recommended for travellers to endemic areas.

HIV/AIDS

HIV (Human Immunodeficiency Virus) destroys CD4 T-cells, progressively weakening the immune system until AIDS develops. Antiretroviral therapy suppresses viral load to undetectable levels, enabling near-normal life expectancy.

Lyme Disease

Lyme disease is a tick-borne bacterial infection caused by Borrelia burgdorferi, presenting with a bull's-eye rash (erythema migrans), flu-like symptoms, and if untreated, joint, neurological, and cardiac complications.

Shingles (Herpes Zoster)

Shingles is reactivation of the varicella-zoster virus (chickenpox virus) in sensory nerves, causing a painful, blistering rash in a dermatomal distribution. Post-herpetic neuralgia is a common and debilitating complication.

Infectious Mononucleosis (Mono)

Infectious mononucleosis, caused by Epstein-Barr virus, presents with severe fatigue, sore throat, swollen lymph nodes, and splenomegaly. It primarily affects adolescents and young adults; strenuous activity must be avoided due to spleen rupture risk.

Streptococcal Pharyngitis (Strep Throat)

Strep throat is a bacterial infection of the throat caused by Group A Streptococcus, causing sore throat, fever, and swollen tonsils. Antibiotic treatment prevents rare but serious complications including rheumatic fever and kidney disease.

Urinary Tract Infection (UTI)

Urinary tract infections are caused by bacteria entering the urethra and bladder, causing painful urination, urgency, and frequency. Women are significantly more affected; E. coli causes about 80% of cases.

Cellulitis

Cellulitis is a bacterial skin infection causing redness, warmth, swelling, and tenderness of the skin and underlying tissue. Streptococcus and Staphylococcus are the most common causes; it requires prompt antibiotic treatment.

Sepsis

Sepsis is a life-threatening systemic response to infection causing organ dysfunction. It is identified by abnormal temperature, heart rate, breathing, and altered mental status; prompt antibiotic treatment and fluid resuscitation are essential.

Appendicitis

Appendicitis is inflammation of the appendix causing progressive right lower quadrant abdominal pain, nausea, fever, and rebound tenderness. Perforation risk increases with delayed treatment; surgical removal (appendectomy) is standard care.

Bacterial Meningitis

Bacterial meningitis is a medical emergency caused by bacteria such as Neisseria meningitidis and Streptococcus pneumoniae infecting the meninges. It causes severe headache, neck stiffness, photophobia, and can rapidly cause brain damage or death.

Osteomyelitis

Osteomyelitis is a bone infection caused by bacteria or fungi, causing localized bone pain, fever, and tenderness. Staphylococcus aureus is the most common causative organism; treatment requires prolonged antibiotics and sometimes surgery.

Norovirus (Stomach Flu)

Norovirus is the leading cause of acute gastroenteritis worldwide, spreading through contaminated food, water, and surfaces. It causes sudden-onset vomiting, diarrhea, and stomach cramps lasting 1-3 days; hydration is the mainstay of treatment.

Salmonellosis

Salmonellosis is a foodborne illness caused by Salmonella bacteria, typically from contaminated poultry, eggs, or raw produce. Symptoms include diarrhea, fever, and abdominal cramps beginning 6-48 hours after exposure; most resolve within a week.

Toxoplasmosis

Toxoplasmosis is caused by the parasite Toxoplasma gondii, transmitted through cat feces, undercooked meat, or vertically to the fetus. It is usually asymptomatic in healthy individuals but can cause severe disease in immunocompromised patients and congenital infection.

Systemic Lupus Erythematosus (SLE)

SLE is a chronic autoimmune disease that can affect multiple organ systems including the skin, joints, kidneys, and nervous system. The characteristic butterfly rash, joint pain, and kidney disease are hallmarks; flares are managed with immunosuppressants.

Crohn's Disease

Crohn's disease is a chronic inflammatory bowel disease that can affect any part of the GI tract from mouth to anus, causing abdominal pain, diarrhea, and malnutrition. Skip lesions and transmural inflammation are pathological hallmarks.

Vasculitis

Vasculitis is inflammation of blood vessel walls, causing a spectrum of diseases based on the size of affected vessels. Symptoms depend on the organs involved and can include skin purpura, peripheral neuropathy, and organ ischemia.

Giant Cell Arteritis

Giant cell arteritis is a vasculitis of large arteries primarily affecting those over 50, causing headache, temporal artery tenderness, jaw claudication, and risk of sudden visual loss. Urgent corticosteroid treatment prevents blindness.

Diverticulitis

Diverticulitis occurs when diverticula (small pouches in the colon wall) become inflamed or infected, causing left lower quadrant pain, fever, and bowel changes. Uncomplicated cases are treated with antibiotics; perforation or abscess may require surgery.

Lung Abscess

A lung abscess is a pus-filled cavity in the lung parenchyma, usually caused by aspiration of oral bacteria in patients with impaired consciousness. It presents with productive cough, fever, and weight loss; prolonged antibiotics are the primary treatment.

Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (extrinsic allergic alveolitis) is an inflammatory lung disease caused by repeated inhalation of organic antigens. Farmer's lung and bird fancier's lung are classic examples; antigen avoidance is the most important intervention.

Tonsillitis

Tonsillitis is inflammation of the palatine tonsils, causing sore throat, difficulty swallowing, fever, and swollen glands. Recurrent bacterial tonsillitis may require tonsillectomy; Group A Streptococcus is the most important bacterial cause.

Mastitis

Mastitis is inflammation of the breast tissue, most commonly occurring during breastfeeding due to blocked milk ducts or bacterial infection (S. aureus). It causes breast pain, redness, warmth, and fever; antibiotics and continued breastfeeding are recommended.

Trichinellosis

Trichinellosis is caused by Trichinella spiralis larvae encysted in muscle tissue, typically acquired from eating undercooked pork or wild game. It presents with fever, periorbital oedema, and severe myalgia. Treatment includes mebendazole and corticosteroids.

Leishmaniasis

Leishmaniasis is caused by Leishmania protozoa transmitted by sandfly bites, presenting in visceral, cutaneous, or mucocutaneous forms. Visceral leishmaniasis (kala-azar) causes fever, splenomegaly, and pancytopaenia. Amphotericin B and miltefosine are first-line treatments.

Food Poisoning

Food poisoning is an illness caused by consuming contaminated food or water. Symptoms typically begin within hours to days of exposure and range from mild discomfort to severe dehydration.

Viral Pharyngitis

Viral pharyngitis is throat inflammation caused by a viral infection, most commonly rhinovirus or adenovirus. It is the most frequent cause of sore throat and resolves without antibiotics.

Acute Laryngitis

Acute laryngitis is sudden inflammation of the larynx typically caused by viral upper respiratory infections. The hallmark is hoarseness or voice loss, usually lasting less than 3 weeks.

Pleurisy

Pleurisy is inflammation of the pleural membranes surrounding the lungs, causing sharp chest pain that worsens when breathing deeply or coughing.

Reactive Arthritis

Reactive arthritis is joint inflammation triggered by an infection elsewhere in the body, usually intestines, genitals, or urinary tract. The classic triad includes joint, eye, and urethral inflammation.

Epididymitis

Epididymitis is inflammation of the epididymis. In men under 35, STIs are the most common cause; in older men, urinary tract bacteria predominate. It requires prompt antibiotic treatment.

Kidney Infection (Pyelonephritis)

Pyelonephritis is bacterial infection of one or both kidneys, usually ascending from a bladder infection. It requires prompt antibiotics to prevent kidney damage and sepsis.

Pelvic Inflammatory Disease (PID)

PID is an infection of the female reproductive organs, usually caused by sexually transmitted bacteria. Untreated, it can lead to infertility, ectopic pregnancy, and chronic pelvic pain.

Giant Cell Arteritis

Giant cell arteritis is inflammation of large and medium arteries in the head. Primarily affecting people over 50, it can cause vision loss if untreated with corticosteroids.

Granulomatosis with Polyangiitis

Granulomatosis with polyangiitis (Wegener's) is a rare form of vasculitis affecting small and medium vessels, primarily targeting the respiratory tract and kidneys.

Viral Meningitis

Viral meningitis is inflammation of the membranes surrounding the brain and spinal cord caused by viruses. Less severe than bacterial meningitis, most cases resolve without specific treatment.

Hepatitis A

Hepatitis A is a highly contagious liver infection caused by the hepatitis A virus, transmitted through contaminated food and water. Unlike hepatitis B and C, it does not cause chronic disease.

Salmonella Infection

Salmonellosis is a common bacterial food poisoning caused by Salmonella bacteria. It typically causes diarrhea, fever, and stomach cramps beginning 12-72 hours after infection.

Diverticulitis

Diverticulitis occurs when small pouches (diverticula) that form in the digestive tract become inflamed or infected. It causes abdominal pain and can lead to serious complications.

Infective Endocarditis

Infective endocarditis is infection of the inner heart lining, particularly the heart valves. It is a serious condition requiring prolonged intravenous antibiotics and sometimes surgery.

Myocarditis

Myocarditis is inflammation of the heart muscle, most commonly caused by viral infections. It can affect the heart's electrical system and pumping ability, ranging from mild to life-threatening.

Ovarian Torsion

Ovarian torsion is the twisting of an ovary around its supporting ligaments, cutting off its blood supply. It causes sudden, severe pelvic pain and is a gynaecological emergency requiring urgent surgical intervention to preserve the ovary.