Aetiology of Fever of Unknown Origin in Two Middle Delta Egyptian Tertiary Health Care Facilities

Fever of Unknown Origin (FUO) was first defined in 1961 as a temperature greater than 38.3°C on several occasions, lasting for more than 3 weeks, or failure to reach a diagnosis despite one week of inpatient investigation. The time frame has recently been revised to include patients whose illness remains undiagnosed after either a minimum of three outpatient visits or three days of hospitalization. The purpose of this study was to describe the etiology, frequency, and pattern of different causes, particularly infectious causes, and to determine the relative incidence of various causes of FUO in the mid-Delta area of Egypt.

This retrospective cohort study included all FUO cases registered in the file system over a seven-year period from 2015 to 2022 at Mahala-Kubra Fever Hospital, as well as all admitted FUO cases at the Tropical Medicine and Infectious Diseases Department of Tanta University during 2021 and 2022.

A total of 383 FUO cases were included in the study. Among these, the leading causes of FUO were infections (n = 334, 87.2%), followed by neoplasms (n = 26, 6.8%). Autoimmune and miscellaneous causes ranked third (n = 9, 2.3%), and undiagnosed cases were the least common (n = 5, 1.3%). The two most common infectious causes in this study were urinary tract infection (n = 136, 40.7%) and brucellosis (n = 115, 34.4%). Typhoid fever (n = 29, 8.7%), pneumonia (n = 15, 4.2%), and abscesses (n = 10, 3.0%) were also frequent causes of FUO. Hematological malignancies were the most common malignant causes of FUO, with lymphoma being the most prevalent (n = 10, 38.5%), followed by leukemia (n = 8, 30.8%).

Fever (pyrexia) of unknown origin remains one of the most challenging complexities in medical diagnosis. Infections, particularly Urinary Tract Infections (UTIs) and brucellosis, are the primary causes of FUO in this study. It is also important to recognize that hematological malignancies are a significant cause of FUO.