Afebrile brucellosis patients in endemic areas: a great diagnostic challenge

Brucellosis is a common zoonotic infection in pastoral areas. The absence of fever in some patients can lead to misdiagnosis or underdiagnosis, resulting in delayed treatment. However, no literature have summarized the clinical features of afebrile brucellosis, and this study aimed to fill in the research gap.

In this retrospective case-control study, patients diagnosed with brucellosis who were admitted to the Affiliated Kashgar Hospital of Sun Yat-sen University in 2024 were included. They were divided into afebrile and febrile groups. Demographic data, clinical features, and laboratory findings were compared between the two groups.

A total of 70 afebrile and 119 febrile patients were included in the study. Compared with febrile patients, afebrile patients had a higher proportion of chronic disease course (20% vs. 10%, p = 0.008) and were more likely to lack a clear epidemiological history (29% vs. 46%, p = 0.025). Afebrile patients were more likely to present with focal infections and localized symptoms, mainly spondylitis (51% vs. 24%, p < 0.001) and dorsalgia (66% vs. 42%, p = 0.003). In contrast, febrile patients were more likely to exhibit systemic toxic symptoms, mainly fatigue (75% vs. 34%, p < 0.001), inappetence (58% vs. 34%, p = 0.003), and hidrosis (37% vs. 17%, p = 0.007). The positive rate of bacterial culture was lower in afebrile patients (40% vs. 66%, p = 0.001). Febrile patients exhibited significantly lower hemoglobin levels, platelet counts, serum calcium and phosphorus levels, but higher procalcitonin levels, elevated transaminase levels, higher γ-glutamyl transferase levels, and a prolonged prothrombin time (all p < 0.05).

The atypical clinical manifestations, lower positive rate of bacterial culture, and fewer abnormal laboratory findings pose a greater diagnostic challenge of afebrile brucellosis. Despite causing less systemic impact, afebrile brucellosis may be associated with a worse prognosis. Physicians in pastoral areas should emphasize etiological diagnosis for afebrile patients presenting with dorsalgia.