# Comparison of Clinical, Epidemiological, Haematological, and Biochemical Characteristics in Serologically Confirmed and Suspected Cases of Tularemia

## TL;DR

This study compares tularemia patients with similar but non-tularemia cases to identify key differences in symptoms and risk factors for better diagnosis.

## Contribution

The study identifies specific clinical and epidemiological markers that distinguish confirmed tularemia cases from similar-looking cases.

## Key findings

- Tularemia cases had longer delays in seeking care and more oropharyngeal symptoms like sore throat and tonsillitis.
- Epidemiological risk factors like rural residence and water contact were more common in tularemia patients.
- Lower levels of alanine aminotransaminase and C-reactive protein were observed in confirmed tularemia cases.

## Abstract

Background: Tularemia is a zoonotic infection caused by Francisella tularensis, transmitted to humans through direct contact with infected animals, arthropod bites, or by ingesting contaminated water. It commonly presents with fever, lymphadenopathy, and oropharyngeal symptoms. In Turkey, where waterborne outbreaks are frequent, tularemia remains a significant public health concern. This study aimed to compare the clinical, epidemiological, and laboratory characteristics of patients diagnosed with tularemia and those with similar clinical features but seronegative results, with the goal of identifying parameters that may assist in differential diagnosis. Methods: This retrospective study included adults (≥18 years) who presented to the Infectious Diseases Outpatient Clinic between 2016 and 2024 with suspected tularemia and were tested using a microagglutination test (MAT). Patients with a positive MAT (≥1:160) or a fourfold titre increase were classified as tularemia cases, while seronegative patients were defined as tularemia-like cases. Demographic data, clinical symptoms, epidemiological risk factors, and laboratory findings were compared between the two groups. Results: A total of 105 patients were included, 54 (51.4%) of whom were diagnosed with tularemia. The duration from symptom onset to healthcare presentation was significantly longer in tularemia cases (20.3 ± 5.7 vs. 15.7 ± 6.2 days; p < 0.001). Sore throat (66.7% vs. 43.1%; p = 0.026) and tonsillitis/pharyngitis (55.6% vs. 21.6%; p = 0.001) were significantly more prevalent in the tularemia group. Epidemiological risk factors, including rural residence (92.6%), animal husbandry (74.1%), agricultural activity (72.2%), and contact with lake or stream water, were significantly more prevalent among tularemia cases (all p < 0.001). Alanine aminotransaminase (p = 0.019) and C-reactive protein levels (p = 0.027) were significantly lower in the tularemia group. Conclusions: Tularemia cases are associated with particular epidemiological risk factors and oropharyngeal symptoms. A thorough epidemiological evaluation is crucial for diagnosis, and enhancing awareness among healthcare providers and the public may facilitate earlier recognition and management.