Merck Manual

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Some Causes of Fever Based on Risk Factors

Some Causes of Fever Based on Risk Factors

Risk Factor


None (healthy)

Upper or lower respiratory tract infection

Gastrointestinal infection

Infection related to a catheter inserted in a vein (IV catheter infection)

Urinary tract infection, particularly in people with a urinary catheter

Pneumonia, particularly in people on a ventilator

Atelectasis (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


Transfusion reaction

Travel to areas where an infection is common (endemic areas)

Disorders that cause diarrhea

Fungal infections such as coccidioidomycosis, blastomycosis, or histoplasmosis

Rickettsial infections (such as African tick-bite fever and Mediterranean spotted fever)

Exposure to insects or animals that carry disease-causing organisms, called vectors (in the United States)

Wild animals: Tularemia, rabies, or hantavirus infection

Fleas: Plague

Birds: Psittacosis

A weakened immune system (immunocompromise)

Parasites: Infection due to Toxoplasma gondii, Strongyloides stercoralis, Cryptosporidium, or Cystoisospora belli

Drugs that can increase heat production

Methylenedioxymethamphetamine (MDMA, or Ecstasy)


Drugs that can trigger fever

Beta-lactam antibiotics (such as penicillin)

Sulfa drugs





Amphotericin B

Interferons (drugs that are based on substances produced by the immune system and that help block the reproduction of viruses)