The causes of prolonged fever have changed during the years and are influenced by age, geographic location and availability of diagnostic facilities/techniques. The aim of the present study was to determine the causes of prolonged fever, to know the proportion and outcomes of undiagnosed children.

We reviewed patients with fever persisting for more than 2 weeks in duration, with documented temperatures of 38℃ on several occasions, or uncertain diagnosis after intensive study of 1 week duration in other hospitals who were admitted to Pusan National University Hospital during the period from July 1999 to June 2004.

Fifty-four (59.0 percent) were boys and thirty-seven (41 percent) were girls. Forty-six cases were less than 6 years and 45 cases were more than 6 years; the mean age was 6.48±6.56 years. In 62 cases (68.1 percent), the fever had persisted for 2 to 3 weeks before admission and in 26 cases (28.6 percent), had lasted longer than a month. Final diagnosis had been reached in 66 of 91 children (72.5 percent). The most common cause was infection (38/91), followed by collagen vascular disease (12/91), immune deficiency (3/91), neoplasia (2/91), and miscellaneous disease. Tuberculosis was the most common infectious cause. The causes of fever were not revealed in 25 cases. Outcome on discharge were as follows; 77 cases (84.6 percent) were improved, 10 cases (11.0 percent) discharged without improvement and 4 cases (4.4 percent) expired.

The most common cause of prolonged fever in Korean children remains infection, but the incidence of infection was decreased as compared with previous studies. Tuberculosis is the most common among infectious causes. As Kikuchi disease (subacute necrotizing lymphadenitis) represented a significant cause of prolonged fever, it should be considered if a patient has neutropenia with lymphadenopathy. Undiagnosed patients with prolonged fever (27.5 percent) have increased over previous studies.