Acute Febrile Illness (AFI): Symptoms, Causes, and Treatment

One day you’re fine, and the next, your body feels hot, achy, and exhausted. Maybe there’s a headache, chills, or just a general sense that something’s off. Doctors often refer to this type of rapid-onset illness as an acute febrile illness.

Acute Febrile Illness (AFI) is a frequently encountered medical condition that affects people of all ages. It is characterized by the sudden onset of fever, typically lasting less than 14 days [1]. Various factors, including a wide spectrum of infections and non-infectious conditions, can cause AFI. Recognising the symptoms and understanding the causes of AFI are crucial for early diagnosis and effective treatment, as the underlying cause can range from a benign viral infection to a life-threatening condition [2].

What is Acute Febrile Illness (AFI)?

Acute Febrile Illness, also known as acute undifferentiated fever or short febrile illness, is defined as a sudden rise in body temperature, generally considered to be above 38.0°C (100.4°F) when measured orally [3]. This elevated temperature is the body’s natural response to fighting off invading pathogens, such as bacteria, viruses, parasites, or fungi. AFI can vary in severity and may be accompanied by other symptoms, such as headaches, chills, muscle pain, and dizziness. While many cases of AFI are self-limiting (resolve on their own), it is essential to identify the underlying cause to provide appropriate care and rule out serious conditions [2].

Common Causes of Acute Febrile Illness (AFI)

AFI refers to a rapid onset of fever, often accompanied by other symptoms such as chills, weakness, and muscle aches. The causes of AFI are diverse and can be broadly categorised into infectious and non-infectious factors. Here are the main causes of AFI:

• Bacterial infections: Examples include Streptococcus (strep throat), E. coli (urinary and gastrointestinal infections), Staphylococcus (skin infections), and Typhoid (often from contaminated food or water) [4].
• Viral infections: Coronavirus, Influenza, Dengue fever, Varicella (chicken pox), Measles, and certain acute presentations of HIV.
• Parasitic infections: Malaria (transmitted by mosquito bite), Lyme disease (transmitted by tick bite), and Giardiasis (from contaminated water).
• Fungal infections: Candida (yeast), Cryptococcus (meningitis), and Pneumocystis (pneumonia), often seen in individuals with weakened immune systems.
• Vector-borne diseases: Dengue fever, Zika virus, and various forms of encephalitis, which are particularly prevalent in tropical and subtropical regions.
• Non-infectious causes: These can include certain cancers (malignancies), heat stroke, autoimmune diseases (like Systemic Lupus Erythematosus), and reactions following immunisations [2].

It is important to note that some non-infectious causes may mimic infections, especially in early stages, and require a careful medical evaluation with appropriate testing for exclusion.

Symptoms of Acute Febrile Illness (AFI)

Here are some of the most common symptoms of AFI:

• Elevated body temperature (fever), typically above 38.0°C (100.4°F) [3].
• Headaches and dizziness
• Sweats and chills
• Muscle and joint pain (Myalgia/Arthralgia)
• Weakness and fatigue
• Respiratory symptoms such as coughing or wheezing
• In infants or young children, fever may be accompanied by seizures (Febrile Seizures)
• Nausea, vomiting, and lethargy in some cases

Treatment and Management of Acute Febrile Illness (AFI)

The treatment and management of acute febrile illness aim to address the underlying cause of the fever while managing symptoms and preventing complications. A specific diagnosis is key to effective management [2].

General Measures (Supportive Care):

• Paracetamol (Acetaminophen) or Ibuprofen may be recommended for fever control and pain relief. Always follow the dosage instructions provided by a healthcare professional or the product label.
• Avoid aspirin or NSAIDs (Non-Steroidal Anti-inflammatory Drugs) in suspected cases of Dengue fever or other hemorrhagic fevers due to the potential risk of bleeding complications.
• Ensure adequate hydration with water, Oral Rehydration Solutions (ORS), or clear fluids, as fever can increase the risk of dehydration.
• Get plenty of rest and maintain a cool environment.

Specific Treatment (Requires Medical Diagnosis):

• Antibiotics: Only prescribed if a bacterial infection is confirmed or strongly suspected by a doctor. Self-medication should be strictly avoided.
• Antivirals: Rarely used; may be prescribed for severe cases of Influenza or specific herpesvirus infections.
• Antimalarials: Prescribed for confirmed cases of Malaria.
• Hospitalisation: Required in severe cases with complications, persistent high fever, hypotension (low blood pressure), or suspected sepsis.

Note: Self-medication with antibiotics or other prescription drugs without a proper medical diagnosis should be strictly avoided to prevent antimicrobial resistance and potential drug-related complications.

Conclusion

Acute Febrile Illness is a common condition with a wide range of causes, making accurate and timely diagnosis essential [4]. While many cases are self-limiting, early identification of the cause is critical to guide treatment, especially in regions prone to infectious outbreaks. Failure to treat AFI where a specific underlying cause is identified (e.g., bacterial infection or malaria) can result in severe complications, but with prompt diagnosis and supportive care, most individuals recover fully. Always seek medical attention for fever that is high (over 39.5°C or 103°F), persistent (lasting more than 72 hours), or accompanied by severe symptoms like confusion, difficulty breathing, or a stiff neck.

Frequently Asked Questions (FAQs)

What are examples of febrile illnesses?

Examples of febrile illnesses include bacterial infections (e.g., streptococcus, E. coli, staphylococcus), viral infections (e.g., coronavirus, influenza, dengue fever), parasitic infections (e.g., malaria, Lyme disease), and fungal infections (e.g., candida, cryptococcus).

How long does an acute febrile illness typically last?

An acute febrile illness is defined as a fever lasting less than 14 days [1]. However, if a fever persists beyond 72 hours or is severe, immediate medical evaluation is necessary.

What is the difference between “febrile” and “fever”?

“Febrile” is an adjective that describes the condition of having a fever, such as a “febrile patient.” “Fever” is the specific symptom of an elevated body temperature.

Who is a febrile patient?

A febrile patient is an individual with an elevated body temperature, typically defined as ≥38°C (100.4°F) or higher, indicating a potential infection or other underlying medical condition.

What is the febrile stage?

It refers to the active period during an illness when the body temperature is elevated. This stage is often associated with symptoms like chills, sweating, and systemic discomfort.

Is an acute febrile illness contagious?

An acute febrile illness can be contagious or not, depending on the underlying cause. For example, AFI caused by viral and bacterial infections is often contagious, while AFI caused by non-infectious conditions (like autoimmune diseases or heat stroke) is not.

What causes a febrile infection?

Febrile infections are caused by various pathogens, including viruses (e.g., coronavirus, influenza), bacteria (e.g., Streptococcus, E. coli), parasites (e.g., malaria, Lyme disease), and fungi (e.g., Candida, Cryptococcus).

References

[1] Rhee, C., Kharod, G. A., Schaad, N., Furukawa, N. W., Vora, N. M., Blaney, D. D., Crump, J. A., & Clarke, K. R. (2019). Global knowledge gaps in acute febrile illness etiologic investigations: A scoping review. PLoS Neglected Tropical Diseases, 13(11), e0007792. https://doi.org/10.1371/journal.pntd.0007792

[2] Grundy, B. S., & Houpt, E. R. (2022). Opportunities and challenges to accurate diagnosis and management of acute febrile illness in adults and adolescents: A review. Acta Tropica, 227, 106286. https://doi.org/10.1016/j.actatropica.2021.106286

[3] Sullivan, J. E., & Farrar, H. C. (2011). Fever and antipyretic use in children. Pediatrics, 127(3), 580–587. https://doi.org/10.1542/peds.2010-3852

[4] Capeding, M. R., Chua, M. N., Hadinegoro, S. R., Hussain, I. I. H. M., Nallusamy, R., Pitisuttithum, P., Rusmil, K., Thisyakorn, U., Thomas, S. J., Tran, N. H., Wirawan, D. N., Yoon, I., Bouckenooghe, A., Hutagalung, Y., Laot, T., & Wartel, T. A. (2013). Dengue and other common causes of acute febrile illness in Asia: An active surveillance study in children. PLoS Neglected Tropical Diseases, 7(7), e2331. https://doi.org/10.1371/journal.pntd.0002331