#50 Fever in the ICU and Fever in the Returning Traveler

Written By Nick Mark

We see fever every day in the ICU but what’s the best approach to diagnosis and when do we need to go on a Zebra hunt? In this episode, we’re joined by Dr. Luis Tatem, a physician triple-boarded in Internal Medicine, Infectious Diseases, and Critical Care — plus certified in Tropical Medicine from the London School of Hygiene & Tropical Medicine. We explore the diagnostic and therapeutic approach to fever in the ICU, including practical pearls for evaluating fevers in patients returning from global travel. We then walk through high-yield case vignettes that illustrate diseases like malaria, dengue, typhoid, leptospirosis, and more.

Luis Tatem, MD

Swedish Medical Center, Seattle WA

Key Learning Objectives

  • Understand how to define and measure fever in critically ill patients.

  • Develop a structured workup for fever in the ICU.

  • Learn how to elicit a high-yield travel history.

  • Recognize high-risk regions, exposures, and pathogens associated with post-travel fevers.

  • Review case-based management of common tropical infectious diseases.


Fever in the ICU: Definitions, Measurement, and Workup

How common is fever in the ICU?
According to the IDSA, 28–88% of ICU patients will experience fever during their admission.

Defining Fever:

  • No single universal threshold. Per UpToDate: “Fever is an elevation in core body temperature above the daily range for an individual. There is no universal threshold for fever, as normal body temperature varies by individual, time of day, and method of measurement”“

  • Often used cutoff for fever is >38.3°C (101°F).

  • For neutropenic patients: >38.0°C sustained for 1 hour, or >38.3°C once (NCCN, IDSA Guidelines).

  • In elderly or LTCF patients, fever may be defined as >37.8°C once, or >37.2°C oral on repeated measurements.

Hyperpyrexia: >41.5°C (106.7°F) — seen in certain toxidromes, CNS causes, or overwhelming infections.

Normal body temperature:

How should we measure temperature in ICU patients? Ideally centrally.

  • Accuracy of different measurement techniques, from most to least reliable:

  1. Pulmonary artery catheter (PAC) 🥇

  2. Esophageal 🥈

  3. Bladder 🥈

  4. Rectal 🥉

  5. Oral 🥉

  6. Tympanic/Skin 🥉

Workup of Fever in the ICU:

  • There is no “generic fever workup” it should be customized to the individual patient risk factors.

  • First step is to examine the patient and talk to their nurse!

  • Labs and studies:

    • Blood cultures ×2 (central + peripheral)

    • Urinalysis and urine culture (change foley if applicable)

    • CBC with differential, LFTs, CRP, Procalcitonin

    • Chest X-ray (for all patients), CT scan if needed

    • Targeted testing depending on presentation:

      • Abdominal US (if GI symptoms)

      • Respiratory viral panel (if URI symptoms)

      • Consider line infections, drug fevers, necrotizing soft tissue infection

Non-Infectious Causes of Fever:

  • Drug fever (e.g. dexmedetomidine, amphotericin, penicillins, )

  • Thrombosis (PE, DVT)

  • Autoimmune disease

  • Malignancy

  • CNS pathology (SAH, central fever)


Fever in the Returning Traveler

Epidemiology:

  • Most illnesses in returning travelers are mild and do not require medical attention, however over 180,000 people entering the US every day.

  • Up to 79% of travelers to low/middle-income countries develop illness during or after travel (CDC Yellow Book). Around 19% of travelers from the developing world will develop fever after returning — many within the first 2 weeks.


High-Yield Travel History Questions:

  • Tourist vs visiting friends/relatives (VFR) (VFR often take fewer precautions)

  • Destinations and dates of travel (be more specific than country, what region, city)

  • Lodging type (rural vs hotel, air conditioning, mosquito net use)

  • Vaccination and prophylaxis history (e.g., malaria prophylaxis, yellow fever vaccination)

  • Food and water exposures (bottled water vs tap water vs camping)

  • Insect bites (mosquitos, flies, etc)

  • Animal exposures —> animal bites, livestock (q-fever)

  • Activities (e.g., freshwater swimming, tattoos, sexual contact)

  • Was anyone sick in the travel group?


Diseases by Incubation Period:

  • <14 Days: Dengue, malaria, leptospirosis, rickettsiae, meningococcus, acute HIV, arboviruses

  • 2–6 Weeks: Hepatitis A/E, amebic liver abscess, acute schistosomiasis

  • >6 Weeks: TB, chronic parasitic infections, leishmaniasis


Geographic Clues:

  • Complete list of diseases to consider by location. (by CDC) Some examples:

  • Sub-Saharan Africa: Malaria, African tick-bite fever, typhoid

  • Southeast Asia: Dengue, typhoid, leptospirosis, scrub typhus, Hepatitis A or E

  • South America: Yellow fever, Chagas, acute diarrheal syndrome

  • Central America: Dengue, Zika, Salmonella, Rickettsia, etc

  • USA: Hantavirus, Babesiosis, Anaplasmosis, RMSF, Ehrlichiosis, Tularemia


Physical Exam Tips:

  • Check for hepatosplenomegaly

  • Look for conjunctivitis, lymphadenopathy

  • Examine skin for rash (rose spots, petechiae, purpura)

  • Perform detailed neurologic exam for AMS, encephalopathy

  • Consider syndromes that include fever:

    • Rash + fever

    • Bleeding + fever

    • Joint paint + fever

    • Hepatitis + fever

    • Abdominal symptoms + fever

    • Multi-organ failure + fever


Initial Labs:

  • CBC with manual diff, LFTs, UA

  • Pancultures: Blood, urine, stool

  • Specific tests:

    • Malaria:

      • Thick and thin blood smears (at least 3 smears performed 8 hours apart)

      • RDT for malaria (HRP2 antigen)

    • NS1 antigen for dengue

    • Serologies based on exposure (e.g., leptospira, typhus)


Case-Based Highlights

Case 1: Malaria

  • Diagnosis: Blood smear with high parasitemia

  • Treatment: IV artesunate (via CDC), monitor parasite load

  • Pearls:

    • Follow the parasite percentage; make sure the parasite load is dropping with therapy

    • Things that don’t work: plasma exchange, steroids.

    • Be cautious with fluids → often necessary but high risk for pulmonary edema

    • Remember that people with malaria can have multiple infections.


Case 2: Dengue

  • Signs: Myalgias, rash, gum bleeding, leukopenia, transaminitis

    • Can present with Encephalitis, myocarditis, and bleeding diathesis

  • Diagnosis: NS1 antigen, tourniquet test

  • Management: Fluids, monitor for capillary leak, avoid transfusion unless necessary

    • Myocarditis can lead to cardiogenic shock

    • Use POCUS to identify fluid collections and assess volume status

    • Transfusions:

      • Repeat CBC q 4 hrs

      • Do not transfuse platelets unless platelets are less than 10k but do transfuse blood

    • Capillary leak syndrome

      • Resuscitate to urine output and normalized cap refill

  • Pearls:

    • CDC Dengue Info

    • Per the CDC: “Almost half of the world's population, about 4 billion people, live in areas with a risk of dengue. Dengue is often a leading cause of febrile illness in areas with risk. Dengue outbreaks are reported frequently in these regions, including many popular tourist destinations in: the Caribbean, Central America, South America, and Southeast Asia”


Case 3: Typhoid

  • Diagnosis: Blood cultures, Widal test

  • Treatment: Ceftriaxone (resistance common)

  • Pearl: Differentiate from typhus (Rickettsia)

Typhus Typhoid
Organism Rickettsia prowazekii (epidemic typhus) and Rickettsia typhi (murine typhus).

Salmonella enterica serotype Typhi.
Spread Spread through the bite of infected fleas, lice, or chiggers.

Transmitted through contaminated food or water that contains the bacteria.
Symptoms High fever, headache, myalgias, and rash. Multi-systemic dz.

High fever, headache, myalgias, and rash
PLUS
Abdominal pain, diarrhea
Region Epidemic typhus:
Africa, central america
Murine typhus:
Worldwide, including US
Scrub typhus:
East and Southeast Asia Pacific and parts of south-central Russia.

 Areas with poor sanitation and inadequate access to clean water and safe food are at highest risk, including South and Southeast Asia, Central and South America, Africa, and the Caribbean
Diagnosis Cultures Cultures

Treatment Doxycycline Ceftriaxone (sensitive)
Azithromycin + Meropenem (resistant)
(do not use quinolones)
Steroids

Case 4: Rickettsia (RMSF)

  • Rash starts on wrists/ankles, spreads centrally

  • Labs: Hyponatremia, thrombocytopenia

  • Treatment: Empiric doxycycline

Case 5: Leptospirosis

  • Key signs: Conjunctival suffusion, jaundice, renal failure

  • Diagnosis: PCR/serology

  • Treatment: Ceftriaxone

Case 6: Yellow Fever

  • Yellow fever typically has two phases

    • Initial (viremic) phase: Fever, myalgia, headache, nausea, conjunctival injection.

    • Toxic phase (in ~15-20%): Returns 24–48 hours later with jaundice, hemorrhage, shock, and multiorgan failure. 

  • These patients can be sick!

    • Hemodynamic instability or shock.

    • Hepatic failure with coagulopathy or encephalopathy.

      • Hepatic encephalopathy may develop from fulminant liver failure.

      • Use ammonia levels and mental status as guides; manage ICP if needed.

    • Renal failure.

    • GI bleeding or hemorrhagic diathesis.

    • Coagulopathy is common due to liver failure and DIC.

      • Monitor INR, platelets, and fibrinogen; use blood products judiciously.

      • Avoid invasive procedures when possible.

  • Diagnosis: PCR, travel history

  • Management: Supportive, ICU-level care

  • WHO Yellow Fever Fact Sheet

Case 7: Lassa Fever

  • West Africa endemic; consider in healthcare workers

  • Symptoms: Fever, chest pain, edema, proteinuria

    • Common findings: facial swelling, mucosal bleeding, proteinuria, sensorineural hearing loss (even in survivors).

  • Diagnosis: RT-PCR

  • Treatment: IV ribavirin (within 6 days ideally)

    • IV ribavirin within 6 days of symptom onset reduces mortality.

      • Continue for 10+ days; monitor for hemolytic anemia and hepatotoxicity.

      • Not effective if started late in critical illness — still used but with less benefit.

  • CDC Lassa Fact Sheet

  • Lassa fever is a viral hemorrhagic illness caused by an arenavirus, endemic to West Africa.

    • Often starts with nonspecific symptoms (fever, sore throat, malaise), but can progress to shock, bleeding, encephalopathy, and multiorgan failure.

    • Think of Lassa in patients with fever + travel to West Africa (especially Nigeria, Sierra Leone, Liberia, Guinea).

  • Hypovolemic shock from capillary leak and GI losses.

  • Renal failure, hepatic dysfunction, and DIC-like coagulopathy.

  • Encephalopathy may occur due to direct viral effects or organ failure.

  • Lassa virus is spread via body fluids (urine, vomit, blood), not airborne, but can cause nosocomial outbreaks. Use contact and droplet precautions at minimum; enhance to full barrier precautions (PPE, N95, face shield, double gloves) in ICU.

    • Notify public health authorities early.

Resources and References

Nick Mark
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