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Risk Factor
Cause
None (healthy)
Upper or lower respiratory tract infection
Gastrointestinal infection
Urinary tract infection Overview of Urinary Tract Infections (UTIs) In healthy people, urine in the bladder is sterile—no bacteria or other infectious organisms are present. The tube that carries urine from the bladder out of the body (urethra) contains no bacteria... read more
Skin infection Overview of Bacterial Skin Infections The skin provides a remarkably good barrier against bacterial infections. Although many bacteria come in contact with or reside on the skin, they are normally unable to establish an infection... read more
Hospitalization Hospital-Acquired Infections People who are admitted to the hospital are at risk of acquiring an infection there. Such infections are called nosocomial infections. In the United States, approximately 4 to 5% of people who... read more
Bloodstream infection related to a catheter inserted in a vein (IV catheter infection)
Urinary tract infection, particularly in people with a urinary catheter
Pneumonia Hospital-Acquired Pneumonia Hospital-acquired pneumonia is lung infection that develops in people who have been hospitalized, typically after about 2 days or more of hospitalization. Many bacteria, viruses, and even fungi... read more , particularly in people on a ventilator
Atelectasis Atelectasis Atelectasis is a condition in which all or part of a lung becomes airless and collapses. Blockage of the bronchial tubes is a common cause of atelectasis. Shortness of breath can develop if... read more (collapse of part of a lung due to an airway blockage, rather than an infection)
Infection or a pocket of blood (hematoma) at the site of surgery
Deep vein thrombosis Deep Vein Thrombosis (DVT) Deep vein thrombosis is the formation of blood clots (thrombi) in the deep veins, usually in the legs. Blood clots may form in veins if the vein is injured, a disorder causes the blood to clot... read more or pulmonary embolism Pulmonary Embolism (PE) Pulmonary embolism is the blocking of an artery of the lung (pulmonary artery) by a collection of solid material brought through the bloodstream (embolus)—usually a blood clot (thrombus) or... read more
Diarrhea (due to Clostridioides difficile–induced colitis Clostridioides (formerly Clostridium) difficile–Induced Colitis Clostridioides difficile (C. difficile)–induced colitis is an inflammation of the large intestine (colon) that results in diarrhea. The inflammation is caused by toxin produced... read more )
Drugs
Transfusion reaction
Pressure sores Pressure Sores Pressure sores are areas of skin damage resulting from a lack of blood flow due to prolonged pressure. Pressure sores often result from pressure combined with pulling on the skin, friction,... read more
Travel to areas where an infection is common (endemic areas)
Malaria Malaria Malaria is infection of red blood cells with one of five species of the protozoa Plasmodium. Malaria causes fever, chills, sweating, a general feeling of illness (malaise), and sometimes... read more
Viral hepatitis Overview of Acute Viral Hepatitis Acute viral hepatitis is inflammation of the liver, generally meaning inflammation caused by infection with one of the five hepatitis viruses. In most people, the inflammation begins suddenly... read more
Disorders that cause diarrhea
Typhoid fever Typhoid Fever Typhoid fever is caused by certain types of the gram-negative bacteria Salmonella. It typically causes a high fever and abdominal pain. Typhoid fever can be spread by consuming food or... read more
Zika virus Epidemic encephalitis Encephalitis is inflammation of the brain that occurs when a virus directly infects the brain or when a virus, vaccine, or something else triggers inflammation. The spinal cord may also be involved... read more , chikungunya Arboviruses Arbovirus, arenavirus, and filovirus are viruses that are spread from animals to people and, with some viruses, from people to people. The animal involved depends on the type of virus. Many... read more , Ebola virus Ebola Virus and Marburg Virus Infections Marburg and Ebola virus infections cause bleeding and organ malfunction. These infections often result in death. Marburg and Ebola infections are spread through handling live or dead infected... read more , Japanese encephalitis Epidemic encephalitis , rabies Rabies Rabies is a viral infection of the brain that is transmitted by animals and that causes inflammation of the brain and spinal cord. Once the virus reaches the spinal cord and brain, rabies is... read more , measles Measles Measles is a highly contagious viral infection that causes various cold-like symptoms and a characteristic rash. Measles is caused by a virus. Symptoms include fever, runny nose, hacking cough... read more , and yellow fever Yellow Fever Yellow fever is a mosquito-borne viral disease that occurs mainly in the tropics. Yellow fever occurs only in the tropical areas of Central Africa, southern Panama, and South America. Some people... read more
Dengue fever Dengue Dengue is a mosquito-borne viral infection that causes fever, generalized body aches, and, if severe, external and internal bleeding (called dengue hemorrhagic fever). About 50 to 100 million... read more
Fungal infections such as coccidioidomycosis Coccidioidomycosis Coccidioidomycosis is an infection, usually of the lungs, caused by the fungus Coccidioides immitis or Coccidioides posadasii. The infection is caused by inhaling spores of the... read more , blastomycosis Blastomycosis Blastomycosis is an infection, mainly of the lungs, caused by the fungus Blastomyces dermatitidis. People have a fever, chills, and drenching sweats and sometimes chest pain, difficulty... read more , or histoplasmosis Histoplasmosis Histoplasmosis is an infection caused by the fungus Histoplasma capsulatum. It occurs mainly in the lungs but can sometimes spread throughout the body. Histoplasmosis is acquired by inhaling... read more
Rickettsial infections Overview of Rickettsial Infections Rickettsial infections and related infections (such as anaplasmosis, ehrlichiosis, and Q fever) are caused by an unusual type of bacteria that can live only inside the cells of another organism... read more (such as African tick-bite fever and Mediterranean spotted fever Other Spotted Fevers Various rickettsiae, transmitted by ticks, cause spotted fevers similar to but milder than Rocky Mountain spotted fever. They cause a small sore at the site of the tick bite, swelling in nearby... read more )
Exposure to insects or animals that carry disease-causing organisms, called vectors (in the United States)
Ticks: Rickettsiosis Overview of Rickettsial Infections Rickettsial infections and related infections (such as anaplasmosis, ehrlichiosis, and Q fever) are caused by an unusual type of bacteria that can live only inside the cells of another organism... read more , ehrlichiosis or anaplasmosis Ehrlichiosis and Anaplasmosis Ehrlichiosis and anaplasmosis are tick-borne bacterial infections that cause fever, chills, muscle aches, headache, a general feeling of illness (malaise), and sometimes a rash. Symptoms of... read more , Lyme disease Lyme Disease Lyme disease is a tick-transmitted infection caused by Borrelia species, primarily by Borrelia burgdorferi and sometimes by Borrelia mayonii in the United States. These... read more , babesiosis Babesiosis Babesiosis is infection of red blood cells caused by the protozoa Babesia. Babesiosis is transmitted by the same type of deer ticks (Ixodidae) that transmits Lyme disease. Babesiosis... read more , relapsing fever Relapsing Fever Relapsing fever is an infection caused by certain Borrelia species, which are spiral-shaped bacteria called spirochetes (see figure ). People are infected when they are bitten by an infected... read more , or tularemia Tularemia Tularemia is infection that is caused by the gram-negative bacteria Francisella tularensis, which is acquired when people have direct contact with infected wild animals, usually rabbits... read more
Mosquitoes: Encephalitis caused by arboviruses Epidemic encephalitis Encephalitis is inflammation of the brain that occurs when a virus directly infects the brain or when a virus, vaccine, or something else triggers inflammation. The spinal cord may also be involved... read more , malaria Malaria Malaria is infection of red blood cells with one of five species of the protozoa Plasmodium. Malaria causes fever, chills, sweating, a general feeling of illness (malaise), and sometimes... read more , or Zika virus infection Zika Virus Infection Zika virus infection is a mosquito-borne viral infection that typically causes no symptoms but can cause fever, rash, joint pain, or infection of the membrane that covers the white of the eye... read more ; yellow fever Yellow Fever Yellow fever is a mosquito-borne viral disease that occurs mainly in the tropics. Yellow fever occurs only in the tropical areas of Central Africa, southern Panama, and South America. Some people... read more
Wild animals: Tularemia, rabies Rabies Rabies is a viral infection of the brain that is transmitted by animals and that causes inflammation of the brain and spinal cord. Once the virus reaches the spinal cord and brain, rabies is... read more , or hantavirus infection Hantavirus Infection Hantavirus infection is a viral disease that is spread from rodents to people. The virus can cause severe infections of the lungs (with cough and shortness of breath) or kidneys (with abdominal... read more
Fleas: Plague Plague and Other Yersinia Infections Plague is a severe infection caused by the gram-negative bacteria Yersinia pestis and often involving the lymph nodes and/or lungs. The bacteria are spread mainly by the rat flea. Depending... read more
Domestic animals: Brucellosis Brucellosis Brucellosis is an infection caused by several species of the gram-negative bacteria Brucella and characterized by fever and bodywide symptoms. Brucellosis is acquired mainly by having... read more , cat-scratch disease Cat-Scratch Disease Cat-scratch disease is infection caused by the gram-negative bacteria Bartonella henselae and transmitted by a scratch or bite from an infected cat, often causing a crusted bump and swollen... read more , Q fever Q Fever Q fever is related to rickettsial diseases and is caused by Coxiella burnetii, which live mainly in sheep, cattle, and goats. Some people have mild symptoms, but most have flu-like symptoms... read more , or toxoplasmosis Toxoplasmosis Toxoplasmosis is infection caused by the protozoan parasite Toxoplasma gondii. Infection occurs when people unknowingly ingest toxoplasma cysts from cat feces or eat contaminated meat... read more
Birds: Psittacosis, bird flu Bird Flu Bird flu is a viral infection with strains of influenza virus that normally occur in wild birds and domestic poultry. The bird flu virus rarely spreads from animals to people (spread to people... read more
Reptiles: Salmonella infection Salmonella Infections The gram-negative bacteria Salmonella typically cause diarrhea and sometimes cause a more serious infection, typhoid fever. People are usually infected when they eat contaminated food... read more
Bats: Rabies Rabies Rabies is a viral infection of the brain that is transmitted by animals and that causes inflammation of the brain and spinal cord. Once the virus reaches the spinal cord and brain, rabies is... read more or histoplasmosis Histoplasmosis Histoplasmosis is an infection caused by the fungus Histoplasma capsulatum. It occurs mainly in the lungs but can sometimes spread throughout the body. Histoplasmosis is acquired by inhaling... read more
A weakened immune system (immunocompromise)
Viruses: Varicella-zoster virus infection Shingles Shingles is a painful skin rash caused by a viral infection that results from reactivation of the varicella-zoster virus, the virus that causes chickenpox. What causes the virus to reactivate... read more or cytomegalovirus infection Cytomegalovirus (CMV) Infection Cytomegalovirus infection is a common herpesvirus infection with a wide range of symptoms: from no symptoms to fever and fatigue (resembling infectious mononucleosis) to severe symptoms involving... read more
Bacteria: Infection due to pneumococci Pneumococcal Infections Pneumococcal infections are caused by the gram-positive, sphere-shaped (coccal) bacteria (see figure How Bacteria Shape Up) Streptococcus pneumoniae (pneumococci). These bacteria commonly... read more , meningococci Meningococcal Infections Meningococcal infections are caused by the bacteria Neisseria meningitidis (meningococci) and include meningitis and sepsis. Infection is spread by direct contact with nasal and throat... read more , Staphylococcus aureus Staphylococcus aureus Infections Staphylococcus aureus is the most dangerous of all of the many common staphylococcal bacteria. These gram-positive, sphere-shaped (coccal) bacteria (see figure ) often cause skin infections... read more , Pseudomonas aeruginosa Pseudomonas Infections Any of several types of the gram-negative bacteria Pseudomonas, especially Pseudomonas aeruginosa, can infect different parts of the body, particularly in people who have serious... read more , Nocardia, or mycobacteria Tuberculosis (TB) Tuberculosis is a chronic contagious infection caused by the airborne bacteria Mycobacterium tuberculosis. It usually affects the lungs, but almost any organ can be involved. Tuberculosis... read more
Fungi: Infection due to Candida Candidiasis Candidiasis is a fungal infection caused by several species of the yeast Candida, especially Candida albicans. The most common type of candidiasis is a superficial infection of... read more , Aspergillus Aspergillosis Aspergillosis is an infection, usually of the lungs, caused by the fungus Aspergillus. A ball of fungus fibers, blood clots, and white blood cells may form in the lungs or sinuses. People... read more , Histoplasma Histoplasmosis Histoplasmosis is an infection caused by the fungus Histoplasma capsulatum. It occurs mainly in the lungs but can sometimes spread throughout the body. Histoplasmosis is acquired by inhaling... read more , Coccidioides Coccidioidomycosis Coccidioidomycosis is an infection, usually of the lungs, caused by the fungus Coccidioides immitis or Coccidioides posadasii. The infection is caused by inhaling spores of the... read more , microsporidia Microsporidiosis Microsporidiosis is infection caused by Microsporidia, which are parasitic fungi. Symptoms depend on the organs infected, but infections can cause diarrhea, other intestinal symptoms, or eye... read more , Pneumocystis jirovecii Causes , or fungi that cause mucormycosis Mucormycosis Mucormycosis is a fungal infection that can be caused by many different molds. Mucormycosis is acquired when spores produced by the mold are inhaled or, much less commonly, when they enter the... read more
Parasites: Infection due to Toxoplasma gondii Toxoplasmosis Toxoplasmosis is infection caused by the protozoan parasite Toxoplasma gondii. Infection occurs when people unknowingly ingest toxoplasma cysts from cat feces or eat contaminated meat... read more , Strongyloides stercoralis Strongyloidiasis Strongyloidiasis is infection caused by the roundworm Strongyloides stercoralis, which enters the body when bare skin comes in contact with soil contaminated with the worm. Usually, people... read more , Cryptosporidium Cryptosporidiosis Cryptosporidiosis is an intestinal infection caused by Cryptosporidium, a protozoan parasite. The main symptoms are abdominal cramping and diarrhea. People acquire the infection by consuming... read more , or Cystoisospora belli
Drugs that can alter body temperature
Amphetamines Amphetamines Amphetamines are stimulant drugs that are used to treat certain medical conditions but are also subject to abuse. Amphetamines increase alertness, enhance physical performance, and produce euphoria... read more
Cocaine Cocaine Cocaine is an addictive stimulant drug made from leaves of the coca plant. Cocaine is a strong stimulant that increases alertness, causes euphoria, and makes people feel powerful. High doses... read more
Phencyclidine Ketamine and Phencyclidine (PCP) Ketamine and phencyclidine are chemically similar drugs used for anesthesia but are sometimes used recreationally. Ketamine is available in powder and liquid form. The powder can be snorted... read more (PCP)
Methylenedioxymethamphetamine Methylenedioxymethamphetamine (MDMA) MDMA (3,4-methylenedioxymethamphetamine) is similar to an amphetamine but has both stimulant and hallucinogenic effects. (See also Amphetamines and Overview of Substance-Related Disorders.)... read more (MDMA, or Ecstasy)
Antipsychotic drugs Neuroleptic Malignant Syndrome Neuroleptic malignant syndrome is confusion or unresponsiveness, muscle rigidity, high body temperature, and other symptoms that occur when certain antipsychotic (neuroleptic) drugs or anti-vomiting... read more (can cause neuroleptic malignant syndrome Neuroleptic Malignant Syndrome Neuroleptic malignant syndrome is confusion or unresponsiveness, muscle rigidity, high body temperature, and other symptoms that occur when certain antipsychotic (neuroleptic) drugs or anti-vomiting... read more )
Anesthetics (inhaled anesthetic gases such as halothane can cause malignant hyperthermia Malignant Hyperthermia Malignant hyperthermia is a rare, life-threatening rise in body temperature that occurs in susceptible people who are given certain muscle-relaxing drugs plus an anesthetic gas for surgery.... read more )
Thyroxine
Interferons (drugs that are based on substances produced by the immune system and that help block the reproduction of viruses)
Drugs that can trigger fever by a hypersensitivity reaction
Beta-lactam antibiotics (such as penicillin Penicillins Penicillins are a subclass of antibiotics called beta-lactam antibiotics (antibiotics that have a chemical structure called a beta-lactam ring). Carbapenems, cephalosporins, and monobactams... read more )
Sulfa drugs
Phenytoin
Carbamazepine
Procainamide
Quinidine
Amphotericin B