Acute Febrile Illness (AFI), that goes by other medical terminologies including Acute Undifferentiated Fever (AUF), Acute Fever (AF) or Short Febrile Illness (SFI) is generally defined as a fever that subsides by itself in three weeks, or in some instances, lasts for a maximum period of a fortnight i.e. two weeks.

Due to the fact that the exact underlying causes of acute febrile illness are yet to be identified, doctors from the medical community worldwide are yet to reach a common consensus on the exact definition of acute febrile illness.

Nevertheless, certain factors can be stated as triggering a rise in body temperature above the normal levels, which is 98.6 Fahrenheit or 37 Celcius and ultimately resulting in acute febrile illness.
acute febrile illness

These include an epidemic of certain infectious diseases due to geographical regions or seasonal changes in a particular country or city. The harmful microbes instigating AFI comprise viruses, bacteria, protozoa and rickettsia that cause malaria, scrub typhus, rickettsial fevers, dengue, leptospirosis and influenza. Furthermore, in a minority of cases, signs of AFI are detected in the patient, but the exact causative aspect cannot be diagnosed. Also Read: Influenza Virus: Debunking Common Myths About The Contagious Disease

Hence, acute febrile illness is broadly categorised into three sub-types, based on the signs and severity of the illness, which are:

Diagnosed Acute Febrile Illness (Diagnosed AFI)

Non-Malarial Acute Febrile Illness (Non-Malarial AFI)

Undiagnosed Acute Febrile Illness (Undiagnosed AFI)

Due to the wide prevalence of AFI, particularly in tropical nations including India, in the monsoons as well as phases between seasonal changes, it is important to understand how AFI presents in people and ensure immediate medical care is given, so as to ensure a speedy recovery.

Symptoms Of Acute Febrile Illness:

The overlapping feature of AFI with other vector-borne illnesses does pose a challenge for physicians to distinguish the symptoms from that of a common cold, viral fever or malarial infection. Specific traits that doctors associate with acute febrile illnesses comprise the following:

  • A high fever that lasts for more than 4 days and does not subside with the usual dose of antibiotics or antivirals, with body temperatures constantly being above normal
  • Rashes on skin
  • Haemorrhages
  • Jaundice
  • Myalgia
  • Arthralgia
  • Typhoid

Diagnosis Of Acute Febrile Illness:

The wide array of indicators that fall under the umbrella of acute febrile illness invariably result in medical practitioners having to conduct various different analyses to certainly conclude an instance of AFI. Besides scrutinizing the external symptoms and medical history of the affected individual, the primary diagnostic tests consist of:

Peripheral Smear Examination

In this test, the medical expert takes a sample of blood from the patient and examines it under the microscope, to look for any anomalies in the structure, number and size of red blood cells, white blood cells and platelets.

Rapid Diagnostic Test (RDT)

A sterilized needle is used to prick the patient and merely a drop of blood is drawn onto an antigen plate. The antigen on the plate is a protein specific to any one of the infectious diseases – malaria, dengue, jaundice, typhoid or other regional diseases. The blood sample is then promptly analysed under a lens, to spot if it binds to the antigen on the plate. Post this analysis, a quick laboratory diagnosis confirming if the viral or bacterial strain causing malaria, dengue, jaundice or typhoid is present in the system of the patient, so as to enable initiating treatment procedures instantly. Also Read: Learn About Prevention Of Malaria In Mosquito Season

ELISA (Enzyme-Linked Immunosorbent Assay)

This biochemical assay utilises an antibody as a ligand (binding agent), to discern if the specific protein called an antigen, which is found on the cell membranes of infectious germs, is present in the blood sample of the patient. The ELISA test is usually used to figure out an instance of rickettsial infections or leptospirosis.

PCR (Polymerase Chain Reaction)

This is a detailed evaluation of the DNA samples in the blood of the patient, wherein they are amplified and the signal is compared to a standard DNA from a healthy individual and the DNA from the causative microbial agent. In case the DNA signal from the patient’s blood sample correlates with that of the infectious microorganism, then the diagnosis of the specific case of AFI can be confirmed.

Treatment Options For Acute Febrile Illness:

Depending on the characteristic features and severity of fevers in the individual afflicted with AFI, the healthcare provider begins the appropriate course of treatment, in order to guarantee the complete elimination of fever symptoms within two to three weeks.

Essentially, antimalarial drugs, antibiotics or antivirals are prescribed, to be taken in a strict course following meals. In addition, multivitamin supplements are also strongly advised to be taken, in order to avoid serious instances of lethargy, dizziness, nausea, vomiting and headaches.


More in-depth research is required to significantly prevent AFI, so as to lower the number of cases of acute febrile illness, especially in tropical countries. Apart from this, investigative studies that clearly outline the causes, symptoms, diagnostic measures and treatment methodologies to efficiently tackle AFI would help doctors treat these ailments successfully and at a quicker pace. This would prevent transmission of AFI amongst a huge, dense population, where infectious germs thrive, as is common in tropical countries and naturally enhance the overall quality of health.