Int J Infect. 2015 January; 2(1): e22906. Published online 2015 January. Research Article Fever of Unknown Origin in Children Aged Three Months to Fifteen Years Gholamreza Solimani 1 ; Elham Shafigji Shahri 1,* ; Zahra Salari 1 ; Mahnaz Shahrakipoor 2 ; Alireza Teimouri 1 1 Children and Adolescent Health Research Center, Zahedan University of Medical Sciences, Zahedan, IR Iran 2 Department of Epidemiology and Biostatistics, Zahedan University of Medical Sciences, Zahedan, IR Iran *Corresponding author: Elham Shafigji Shahri, Children and Adolescent Health Research Center, Zahedan University of Medical Sciences, Zahedan, IR Iran. Tel: +98-9153163460, E- mail: eshahri@yahoo.com Received: August 19, 2014; Accepted: August 19, 2014 Background: Fever of unknown origin (FUO) is defined as the presence of fever in a child for eight or more days that a careful history and physical examination and preliminary laboratory results failed to reveal the probable cause of the fever. The causes of FUO are different according to geographical regions and age. Objectives: The current study aimed to evaluate the common causes of childhood FUO in Zahedan, Iran. Patients and Methods: A six-year retrospective study was conducted on all admitted children aged from three months to fifteen years from January 2006 to January 2012 and those with the final diagnosis of FUO were selected for the study. Results: Finally, 1100 patients were found eligible for the study. The FUO causes were infectious diseases (55.1%), collagen vascular (4.6%), neoplasm (6.7%), miscellaneous (23.3%) and undiagnosed (10.3%). Conclusions: Most fever of unknown origin results from atypical presentation of common diseases like Tuberculosis, Salmonellosis, Brucellosis, and Pneumonia. Keywords:Pediatrics; Infectious Diseases; Children Copyright © 2014, Infectious Diseases and Tropical Medicine Research Center. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (http://creativecommons.org/licenses/by-nc/4.0/) which permits copy and redistribute the material just in noncommercial usages, provided the original work is properly cited. 1. Background Fever is defined as a centrally mediated elevation of body temperature in response to a stress or insult. De- fining the limits of normal body temperature however is more difficult. Generally, the accepted range of rectal temperature is from 36°C to 37.8°C. Children tend to have higher body temperature than adults (1). Fever is one of the most common complaints in children and the sec- ond reason for referring to a physician. Based on history and physical examinations, a specific cause is not found for about 5% to 20% of febrile patients (1, 2). Fever with un- known resource is defined as a body temperature above 38.3°C which lasts for eight days or more and no clear cause is found fir it despite providing physical and labora- tory evaluation and general screening. One of the major causes of mortality and morbidity in children is Fever of unknown origin (FUO) in the developing countries. The most common causes of FUO in children are infectious diseases (40%-50%), collagen vascular disease with a lower incidence of 10% to 20%, and malignancies with the inci- dence of 5% to 10% (1, 3, 4). Malignancies are more unusual causes for FUO in children compared with adults and are counted for 10% of the cases. Approximately in 15% to 25% of the patients suffering from FUO the cause could not be diagnosed. The majority of hidden infections which cause FUO are unusual presentations of a common disease. The various diseases in children, presented as FUO, differ ac- cording to the geographical regions and depend on the specific diseases in the area and their diagnostic conve- niences (3). Many of the infectious causes of FUO in chil- dren are often bacterial and viral infections including cat scratch disease, Salmonellosis, Brucellosis, Tuberculosis, Human Immunodeficiency Virus (HIV), Cytomegalovirus (CMV), Epstein-Barr virus (EBV) and hepatitis. Local bacte- rial infections usually include endocarditis, intra-abdomi- nal abscess, liver abscess, and sinusitis or mastoiditis, and pyelonephritis or pre renal abscess. The incidence prob- ability of infectious disease and collagen vascular for the majority of FUO is more dominant in children under six years. Inflammatory diseases that usually appear as FUO include rheumatoid arthritis, juvenile rheumatoid arthri- tis (JRA), systemic lupus erythematous (SLE), polyarthritis nodosa, rheumatic fever and Kawasaki. Among malignant diseases, Hodgkin lymphoma, Non-Hodgkin lymphoma, leukemia, Ewing sarcoma, sarcoma and neuroblastoma are more common than the others (1). The FUO treatment should not be started before determining its cause unless the patient is acutely ill. It must be considered because non-specific treatment is rarely effective and delays the diagnosis. There is an exception, to avoid serious compli- cations in neutropenic patients, after taking blood cul-