Fever in Adults

What Is a Fever?

Body temperature varies through the day and with activity, hormones, surroundings and the measurement site. Many clinical services use 38°C as a practical adult fever threshold, but someone can feel hot, cold or shivery even when the measured value is below this.

How Should Temperature Be Measured?

• Use a working digital thermometer and follow its instructions.
• Record the value, time and measurement site because mouth, armpit, ear and forehead readings can differ.
• Wait after a hot or cold drink, bathing, heavy exercise or being wrapped in thick bedding before repeating an oral or surface reading.
• Use the same method for trends when practical rather than comparing several devices and sites.
• Do not repeatedly check every few minutes; reassess if symptoms change or at the interval advised clinically.

Touch alone cannot measure fever reliably. Tell the clinician about chills or rigors even if a thermometer was unavailable.

Fever, Feeling Hot and Heat Illness Are Different

Symptoms That Help Locate the Cause

Common Categories of Causes

• Viral respiratory or gastrointestinal infections.
• Bacterial infections involving the throat, lungs, urinary tract, skin, abdomen, bloodstream or another site.
• Mosquito-borne infections such as dengue or malaria, depending on exposure and local activity.
• Inflammatory or autoimmune conditions.
• Reactions following vaccination, procedures or selected prescribed substances.
• Less commonly, blood disorders, cancers or blood clots.

Symptoms overlap. Fever alone cannot distinguish viral from bacterial illness and cannot show whether an antibiotic is needed.

Dengue Warning Signs

Dengue may cause fever, severe headache, pain behind the eyes, body aches, nausea or rash. Severe dengue can begin as the temperature settles, so a falling fever does not always mean recovery.

• Severe or increasing abdominal pain.
• Persistent vomiting or inability to drink.
• Bleeding from the nose or gums, blood in vomit or stool, or unusual bruising.
• Rapid breathing, marked weakness, restlessness or unusual drowsiness.
• Pale, cold or clammy skin, intense thirst, faintness or reduced urine.

These warning signs need immediate medical care. Do not use a single platelet value to decide severity or delay review while waiting for a repeat test.

Who Needs Earlier Medical Review?

• Pregnant or recently postpartum patients.
• Adults who are older, frail, bedbound or living with dementia.
• People receiving cancer treatment, immune-suppressing care, or living with a weakened immune system.
• People without a functioning spleen, or with a transplant, dialysis, advanced kidney or liver disease.
• Anyone with a recent operation, hospital admission, wound, catheter, line, implant or invasive procedure.
• People with poorly controlled diabetes or significant heart or lung disease.
• Anyone recently exposed to malaria, dengue, contaminated water, animal bites, ticks or a relevant outbreak.

In these groups, contact a clinician promptly even when the temperature is only mildly raised or the symptoms seem early.

When Should a Routine Fever Become a Same-Day Review?

• The fever is worsening, repeatedly returning or not beginning to improve after two to three days.
• There are shaking chills, increasing pain, a new rash or a new localising symptom.
• Drinking is difficult, urine is reduced, dizziness occurs on standing or weakness is increasing.
• The fever follows recent travel, mosquito exposure, surgery, a procedure or a new wound.
• Symptoms improve and then return with greater severity.
• The person is worried because the illness feels substantially different from an ordinary infection.

What Happens During Assessment?

The clinician will ask when symptoms began, the highest measured temperature and site, fever pattern, contacts, travel, mosquito exposure, food and water history, recent procedures, medical conditions and every prescribed or non-prescribed substance taken.

Examination may include pulse, blood pressure, breathing rate, oxygen level, hydration, mental state, skin and the body system suggested by symptoms. These observations help assess urgency and possible sepsis.

Which Tests May Be Needed?

Not every fever needs every test. Timing matters: some tests can be negative early, while others may be misleading if ordered without a compatible history.

• Blood count and selected inflammation or organ-function tests.
• Urine testing when urinary symptoms, pregnancy or no clear source is present.
• Tests for dengue, malaria or other infections based on timing and exposure.
• Respiratory testing when compatible symptoms or an outbreak is present.
• Chest imaging, ultrasound or another scan when examination suggests a particular source or complication.
• Cultures before treatment when a bloodstream, urinary or other bacterial infection is suspected and timing allows.

Safe Supportive Care While Arranging Review

• Rest and drink suitable fluids regularly unless a clinician has restricted fluid intake.
• Wear comfortable light clothing and keep the room reasonably cool; avoid heavy wrapping.
• Record temperature, urine output and important symptoms without checking obsessively.
• Use separate drinking utensils and sensible hand hygiene when an infection may spread.
• Stay away from work, school, food handling and vulnerable people while actively febrile or contagious.

Avoid ice baths, alcohol rubs, leftover prescriptions, shared tablets and unverified injections. If symptom relief is needed, obtain individual advice because pregnancy, dengue risk, allergies, kidney or liver disease and other prescriptions can change what is safe.

Why Antibiotics Are Not Automatic

Antibiotics treat selected bacterial infections; they do not treat viral illness. Unnecessary or incomplete antibiotic use can cause harm, obscure test results and contribute to resistance. When a serious bacterial infection is suspected, timely clinician-directed treatment is important.

Pregnancy and Fever

Fever during pregnancy or soon after delivery deserves earlier clinical advice. Urinary infection, respiratory illness, dengue and pregnancy-related infection may need specific assessment. Seek urgent care for abdominal pain, bleeding, reduced fetal movement, severe headache, breathing difficulty, fainting, confusion or rapidly worsening illness.

When Is Specialist or Higher-Centre Care Appropriate?

• Sepsis, meningitis, severe dengue, malaria complications or another life-threatening infection is suspected.
• There is organ dysfunction, low oxygen, shock, altered consciousness or severe dehydration.
• Fever persists without a clear cause despite appropriate initial evaluation.
• Complex immune suppression, pregnancy, transplant care or serious heart, lung, kidney or liver disease changes management.
• A deep abscess, infected implant or condition requiring advanced imaging, intervention or intensive monitoring is suspected.

Common Myths