What Causes Intermittent Fever in Adults? Your Comprehensive Guide

September 29, 2025 •

4 min read

An estimated 95% of adult fevers are caused by underlying infections, but when a fever comes and goes, the cause can be less obvious.

Understanding what causes intermittent fever in adults is crucial for proper diagnosis and treatment, as this pattern of temperature fluctuation can signal a range of conditions from simple viral illnesses to more complex autoimmune disorders.

Quick Summary

Intermittent fever in adults can be triggered by various underlying conditions, including both acute and chronic infections, autoimmune diseases like rheumatoid arthritis, certain inflammatory syndromes, and, in rare cases, malignancies. The cyclical nature of the fever is a key symptom that helps guide medical professionals toward a diagnosis and appropriate treatment plan.

Key Points

Pattern Recognition: The cyclical pattern of an intermittent fever is a crucial clue for diagnosis, helping doctors distinguish it from continuous or remittent fevers.
Infections are a Common Cause: Viral infections (like EBV), bacterial infections (like UTIs and abscesses), and parasitic infections (like malaria) are frequent culprits.
Autoimmune Diseases Trigger Flares: Conditions such as rheumatoid arthritis and lupus can cause intermittent fever as part of an inflammatory flare-up.
Medication Side Effects: Some drugs can induce a fever that comes and goes; this typically resolves after discontinuing the medication.
Comprehensive Diagnosis is Necessary: Because the causes are diverse, a doctor will perform blood tests, imaging, and other specialized exams to pinpoint the root cause.
Know When to See a Doctor: Seek professional medical help for unexplained, persistent, or severe intermittent fever to ensure proper diagnosis and treatment.

Understanding the Pattern of Intermittent Fever

Intermittent fever is defined as a fever that occurs in cycles, with periods of elevated temperature followed by periods of normal or subnormal temperature. This contrasts with a continuous fever, where the temperature remains elevated, or a remittent fever, which fluctuates but never returns to baseline.

Observing the fever's pattern is often a critical piece of information for a doctor. The timing and duration of the fever spikes, along with other symptoms, can narrow down the potential culprits and help pinpoint the correct diagnosis. For instance, some fevers may follow a predictable 24, 48, or 72-hour cycle, a classic sign associated with specific infectious agents.

Common Infectious Causes

Infections are a leading cause of intermittent fever in adults. The body's immune response to a pathogen often involves raising its core temperature to create a less hospitable environment for the invading organism. The intermittent pattern can reflect the lifecycle of the pathogen or the body's fluctuating battle against it.

Bacterial Infections

Urinary Tract Infections (UTIs): Persistent or complicated UTIs can sometimes lead to intermittent fevers, especially if the infection has spread to the kidneys. The fever may rise and fall as the bacteria multiply and the body fights back.
Abscesses: A localized collection of pus, or an abscess, can be a source of intermittent fever. As the abscess grows and puts pressure on surrounding tissues, it can trigger a systemic inflammatory response. This can include abscesses in the abdomen, liver, or other organs.
Tuberculosis (TB): Although less common in developed nations, TB is a significant global cause of intermittent fever, often accompanied by night sweats, fatigue, and weight loss.

Viral Infections

Epstein-Barr Virus (EBV): The virus that causes mononucleosis can sometimes produce a relapsing fever pattern that lingers for weeks or even months after the initial illness subsides.
Cytomegalovirus (CMV): A common virus similar to EBV, CMV infection can also result in long-term, low-grade, or intermittent fevers in adults.

Parasitic and Vector-Borne Infections

Malaria: A classic example of intermittent fever, malaria involves fever cycles that correspond to the parasite's development inside red blood cells. The fever pattern can be a tertian (every 48 hours) or quartan (every 72 hours) cycle, depending on the species of plasmodium.

Autoimmune and Inflammatory Conditions

When the immune system mistakenly attacks the body's own tissues, it can cause chronic inflammation that manifests as an intermittent fever. These conditions are often accompanied by other systemic symptoms, such as joint pain, rash, or fatigue.

Rheumatoid Arthritis (RA) and Systemic Lupus Erythematosus (SLE)

Both RA and SLE are autoimmune diseases that can cause periodic fever. The fever is typically part of a flare-up of the disease, and can be accompanied by joint swelling, pain, and general malaise.

Adult-Onset Still's Disease (AOSD)

AOSD is a rare inflammatory disease characterized by high-spiking fevers, often occurring once or twice a day, accompanied by a fleeting pink or salmon-colored rash and joint pain. The fever often spikes in the late afternoon or evening.

Medications and Other Non-Infectious Causes

Sometimes, the cause of intermittent fever isn't an infection or autoimmune disease but an adverse reaction to a medication or another systemic issue.

Drug-Induced Fever

Certain medications, including some antibiotics and anticonvulsants, can cause a fever as a side effect. This is known as drug-induced fever and typically resolves once the medication is stopped.

Comparison of Common Causes


Cause	Typical Pattern	Accompanying Symptoms	Diagnostic Clues
Infections	Variable, can be cyclic (e.g., malaria)	Chills, fatigue, specific organ symptoms (cough, pain during urination)	Blood tests (CBC, cultures), imaging, travel history
Autoimmune	Often linked to flare-ups	Joint pain, rash, fatigue, unexplained weight loss	Specific autoantibody tests, inflammatory markers
Drug-Induced	Starts days to weeks after new medication	Rash, lack of other infection signs	Cessation of medication leads to resolution
Malignancy	Often low-grade, persistent, or spiking	Night sweats, unexplained weight loss, fatigue	Blood tests, imaging, biopsy

Diagnostic Approaches

Diagnosing the cause of an intermittent fever can be a methodical process. A doctor will typically start with a thorough medical history, including recent travel, new medications, and a review of all symptoms. Key diagnostic steps include:

Blood Tests: A complete blood count (CBC), inflammatory markers (CRP, ESR), and blood cultures can help identify infection or inflammation. Specific antibody tests may be used to check for autoimmune conditions.
Imaging: Chest X-rays, CT scans, or ultrasounds may be used to check for abscesses, infections, or other sources of inflammation within the body.
Specialized Tests: Depending on the suspected cause, further investigation might involve an antinuclear antibody (ANA) test for lupus, joint fluid analysis for RA, or specific tests for infectious diseases like malaria.

When to Seek Medical Attention

While a mild, intermittent fever from a common cold or flu may resolve on its own, it's important to consult a doctor, especially if the fever is persistent or accompanied by other worrying symptoms. Prompt diagnosis is key to preventing complications from more serious conditions.

Conclusion

Intermittent fever in adults can be a perplexing symptom, but it's not a condition in itself. It is a sign that your body is grappling with an underlying issue, whether it's a persistent infection, a chronic inflammatory disorder, a medication side effect, or another illness. By paying close attention to the fever's pattern and accompanying symptoms, you can provide your healthcare provider with the necessary information to guide them toward an accurate diagnosis. Always seek professional medical advice for a fever that is unexplained, persistent, or accompanied by other concerning symptoms. For additional insights into infectious diseases, you can consult reliable sources on health information like the Centers for Disease Control and Prevention.

Frequently Asked Questions

Not necessarily. While some serious conditions can cause it, intermittent fever can also be a symptom of a simple viral illness or a mild infection. However, because it can also indicate more complex issues, it warrants medical evaluation if it persists or is accompanied by other concerning symptoms.

Doctors use a combination of methods. They take a detailed medical history, noting the fever's pattern, duration, and other symptoms. They also rely on blood tests, such as a complete blood count and inflammatory markers, and sometimes imaging studies to rule out specific infections or inflammatory conditions.

Yes, chronic stress can cause a persistent, low-grade fever, sometimes with a fluctuating pattern, known as psychogenic fever. This typically occurs in people with chronic fatigue syndrome or fibromyalgia. Anti-anxiety treatments are often more effective than traditional fever reducers in these cases.

An intermittent fever involves temperature spikes followed by periods of normal temperature. In contrast, a continuous fever stays elevated for an extended period, with minimal fluctuation.

Yes, certain patterns can be indicative of specific conditions. For example, a fever that spikes every 48 or 72 hours is a classic sign of malaria. Adult-onset Still's disease is often characterized by fever spikes in the late afternoon or evening.

While not a common cause, allergic reactions, including hypersensitivity to certain medications or foods, can sometimes trigger intermittent fevers. This is often an immune response to the allergen.

Immediate medical attention is necessary if the fever is very high (above 103°F), lasts more than a few days, or is accompanied by severe symptoms like confusion, severe headache, chest pain, or difficulty breathing.