Fever of unknown origin can cause various microorganisms and many infectious diseases. We will discuss here only some of them. Infection can be classified by its localization (sinusitis, pneumonia, pelvic abscess, osteomyelitis, etc.) or by the causative agent (leptospirosis, brucellosis, staphylococcal infection, etc.). When treating a patient with fever of unknown origin, a physician should use both classifications.
Upper respiratory tract infections. Infections of the ear, nose, and throat, including banal infections of the upper respiratory tract, especially common in children, are rarely seen for fever of unknown origin for several reasons. Most of these infections go away after a short time, even without treatment, and long fever is not characteristic of them. Doctors are familiar with these diseases and, on the basis of clinical symptoms, generally correctly diagnose.
These infections usually respond well to antibiotic treatment and are often cured unintentionally or accidentally when prescribing antibiotics for other diseases.
Nevertheless, in the published consolidated papers on fever of unknown origin, these diseases are mentioned. So, Pizzo in a series of 100 patients with fever of unknown origin, which was defined as a fever lasting more than 2 weeks, noted 3 cases of sinusitis, 2 cases of tonsillitis and 1 case of peritonsillar abscess. The article, however, does not explain why tonsillitis and peritonsillar abscess have not been diagnosed for such a long time.
In the McClung rabbit, in which fever of unknown origin was identified as a febrile illness that was not diagnosed for 3 weeks of examining a patient on an outpatient basis and 1 week in a hospital, 2 cases of chronic sinusitis were described. The reason for such a late diagnosis was that chronic sinusitis “was not taken into account as a diagnosis.” In 2 cases, the diagnosis of “chronic pharyngitis” in this article is puzzling. In one patient, this disease lasted 2 years!
The available information is not enough to decide whether this child has experienced repeated outbreaks of infection, whether it was a prolonged pharyngitis. Lohr in a series of 54 children with fever of unknown origin included one case of recurrent otitis and one case of sinusitis. Infections of bones and joints. Infectious diseases of bones and joints, as a rule, are clinically easy to diagnose. For fever of unknown origin, bone damage is more common than septic arthritis. Most of the observations of children with fever of unknown origin include several cases of osteomyelitis. Brewis notes that infectious lesions of the pelvis, scapula, and especially of the spine may not be diagnosed for a long time. According to Pizzo, one case of osteomyelitis was observed in the age group under 6 years old and one in the group of children over 6 years old.