Introduction

Fever is one of the most common clinical symptoms encountered across all age groups. In adults and elderly people, however, acute fever carries a particularly important clinical significance. Unlike children—where most fevers are viral and self-limiting—fever in adults and older adults often indicates an underlying infection, systemic disorder, inflammatory condition, or even a life-threatening emergency. The clinical approach must therefore be systematic, evidence-based, and age-specific.

This comprehensive article explains the causes, risk factors, clinical evaluation, red-flag signs, diagnostic methods, and treatment principles of acute fever in adults and elderly individuals. It also highlights how fever behaves differently in older adults, why early diagnosis matters, and what preventive measures can reduce morbidity.

1. What Is Acute Fever?

Fever is defined as:

≥38°C (100.4°F) when measured orally
≥38.2°C (100.8°F) rectally
≥37.8°C (100°F) axillary (less reliable)

Acute fever refers to:

Fever lasting < 7 days, usually due to infections
Subacute: 7–14 days
Chronic/persistent: >14 days

In elderly patients, fever may be mild or even absent despite serious infection due to:

Reduced immune response (immunosenescence)
Blunted temperature regulation
Use of steroids or anti-inflammatory drugs

Thus, elderly fever must always be taken seriously.

2. Pathophysiology: Why Fever Occurs

Fever is a defensive physiological response produced by the hypothalamus. Pyrogens trigger cytokine release—IL-1, IL-6, TNF-α—raising the thermoregulatory set point.

Benefits of fever:

Enhances white blood cell activity
Slows bacterial and viral growth
Improves host immune response

Dangers of fever in adults and elderly:

Dehydration
Delirium, confusion
Seizures (rare in adults)
Stress on heart in patients with cardiac disease

3. Causes of Acute Fever in Adults

The majority are infectious, but non-infectious causes must also be considered.

A. Infectious Causes

1. Viral Infections – Most Common

Influenza
Dengue, Chikungunya
COVID-19
Viral gastroenteritis
Respiratory viruses (RSV, Adenovirus)

Symptoms: Body pain, headache, dry cough, sore throat, mild diarrhoea.

2. Bacterial Infections – High Risk

Urinary tract infection (UTI)
Pneumonia
Skin infections (cellulitis, abscess)
Bacterial meningitis
Typhoid fever
Tuberculosis
Dental infections
Sepsis (life-threatening)

3. Parasitic Infections

Malaria
Amoebiasis
Leptospirosis (especially during monsoon)

B. Non-Infectious Causes

Although less common, these are crucial.

1. Autoimmune and Inflammatory

Rheumatoid arthritis
Systemic lupus erythematosus
Vasculitis
Inflammatory bowel disease

2. Drug-Induced Fever

Antibiotics (penicillin, cephalosporins)
Anti-seizure medications
Antihistamines
NSAIDs

3. Malignancies

Lymphoma
Leukemia
Solid organ cancers (lung, colon)

This is called neoplastic fever.

4. Miscellaneous Causes

Heat stroke
Thyroid storm
Blood transfusion reaction

4. Special Considerations: Fever in Elderly People

The elderly respond very differently to fever due to:

1. Blunted Immune Response

Fever may be absent or mild despite severe infection.
A temperature of 37.5°C (99.5°F) may indicate infection.

2. Atypical Symptoms

Older adults may present with:

Confusion
Fall
Reduced appetite
Weakness
Worsening of existing disease (COPD, heart failure)

3. Higher Risk of Complications

Pneumonia mortality increases significantly
Sepsis progresses rapidly
UTIs can cause delirium or septic shock
Dehydration occurs faster

4. Polypharmacy

Medications like steroids, beta-blockers, and anti-inflammatories mask fever.

Therefore, any acute fever in elderly requires urgent evaluation.

5. Clinical Presentation

Common Symptoms with Fever

Chills, rigors
Headache
Body pains
Cough or breathlessness
Diarrhoea or vomiting
Burning sensation during urination
Localized pain (ear, throat, abdomen)

Red-Flag Symptoms

Immediate medical attention required:

Difficulty breathing
Chest pain
Severe headache or neck stiffness
Persistent vomiting
Confusion or altered sensorium
Purple rash (possible meningococcemia)
Seizure
Very high temperature > 103°F (39.4°C)

6. Diagnostic Approach to Acute Fever

A systematic evaluation is essential.

A. Clinical History

Duration of fever
Pattern (continuous, remittent, intermittent)
Travel history
Mosquito exposure
Sexual history
Animal exposure
Drug history
Vaccination status
Recent hospitalization or catheter use

B. Physical Examination

Vitals (HR, BP, RR, SpO₂)
Skin inspection for rashes
Throat, lungs, abdomen
Neurological evaluation
Joint swelling
Urinary signs

C. Laboratory Investigations

Basic Tests

CBC (WBC count often elevated)
ESR, CRP
Liver & kidney function
Urinalysis and urine culture
Blood culture
Chest X-ray
Dengue NS1, malaria smear/rapid test
Influenza test

Advanced Tests (Based on need)

CT chest/abdomen
Lumbar puncture (suspected meningitis)
Thyroid function
Autoimmune markers
Procalcitonin (bacterial infection severity)

7. Management of Acute Fever

Treatment depends on underlying cause, not fever alone.

A. General Measures

Stay hydrated
Oral rehydration salts
Light clothing
Lukewarm sponge bath
Adequate rest
Avoid alcohol or smoking

B. Medications

1. Antipyretics

Paracetamol 500–650 mg every 6 hours
(Avoid exceeding 3 g/day; elderly need dose adjustment)

2. NSAIDs (if needed)

Ibuprofen
(Avoid in kidney disease, gastritis, heart disease)

C. Antibiotics

Only when bacterial infection is confirmed or strongly suspected:

UTI
Pneumonia
Skin infections
Typhoid
Sepsis

Overusing antibiotics leads to resistance and complications.

D. Antiviral/Specific Therapies

Oseltamivir for influenza
Acyclovir for herpes zoster
Artemisinin combination therapy for malaria
Doxycycline for leptospirosis

E. Hospitalization Criteria

Elderly patient with comorbidities
Low BP
Sepsis or shock
Hypoxia
Altered mental status
Pneumonia
Severe dehydration
Persistent high fever >3 days

8. Complications

Fever itself is usually not dangerous, but delayed treatment is.
Complications include:

Adults:

Severe dehydration
Acute kidney injury
Pneumonia complications
Sepsis

Elderly:

Delirium
Falls
Multi-organ dysfunction
Rapid progression to septic shock

9. Prevention of Acute Infections

A. Vaccination

Especially for elderly:

Influenza vaccine
Pneumococcal vaccine
COVID-19 boosters
Hepatitis B
Shingles vaccine

B. Hygiene

Handwashing
Avoiding contaminated food/water
Safe mosquito control

C. Chronic Disease Management

Better control of:

Diabetes
Hypertension
COPD
Kidney disease

10. When to Consult a Doctor

Seek immediate help if:

Fever > 3 days
Fever with rash
Severe sore throat
Difficulty breathing
Blood in urine or stool
Confusion or severe weakness
Persistent vomiting
In elderly: any mild fever with lethargy or confusion

11. Prognosis

Most viral fevers resolve in 3–5 days.
Bacterial infections recover well with early treatment.
Elderly outcomes depend on:

Early diagnosis
Comorbidity control
Prompt hospitalization when needed

Relevant Website Links (Authoritative Sources)

These are high-quality medical references relevant to fever evaluation and management:

World Health Organization (WHO) – Fever & Infectious Diseases
https://www.who.int/health-topics
Centers for Disease Control and Prevention (CDC) – Adult infections
https://www.cdc.gov
Mayo Clinic – Fever in Adults
https://www.mayoclinic.org/symptoms/fever
NHS UK – Fever in Adults
https://www.nhs.uk/conditions/fever-in-adults
Johns Hopkins Medicine – Symptoms & Conditions
https://www.hopkinsmedicine.org/health
UpToDate (Clinical Guidance)
https://www.uptodate.com
Cleveland Clinic – Fever Causes & Treatment
https://my.clevelandclinic.org/health/symptoms/15159-fever

References

Journal of General Internal Medicine – Diagnostic approach to febrile illness.

WHO. Clinical management of infectious diseases.

CDC. Guidelines for adult infection evaluation.

Mayo Clinic. Fever in adults: symptoms and treatment.

NHS Clinical Guidance. Fever assessment in adults.

UpToDate: “Evaluation of fever in adults”.

Cleveland Clinic. Fever: symptoms, causes, management.

Lancet Infectious Diseases – “Fever in the elderly: atypical presentations”.

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Managing Acute Fever in Adults and Elderly – Expert Guide by Dr. Pothireddy Surendranath Reddy