Clinical characteristics of and diagnostic approaches to human Francisella tularensis infection: a retrospective, monocentric case study from Germany

Francisella tularensis, the causative agent of tularemia, poses a challenge for diagnosis and treatment due to its diverse clinical presentations and low incidence. Hence, the awareness among clinicians is comparatively low. This study reports the clinical characteristics, diagnostic approaches, and treatment outcomes of tularemia cases at one tertiary center in Germany over a 12-yearperiod. This retrospective monocentric case series considered all tularemia cases diagnosed at Saarland University Medical Center in Homburg, Germany between January 2013 and December 2024. Cases were identified from electronic medical records, and the certainty of tularemia was graded as definite, probable and possible infection, based on results of serology, polymerase chain reaction (PCR) assays, or blood cultures. Clinical data were extracted from patient records and supplemented by follow-up information from the clinicians. We identified 14 tularemia cases, including 6 definite as well as 3 probable and 5 possible cases. The clinical presentation was highly variable, with the (ulcero-)glandular form being the most common entity (10/14). Invasive diagnostics or surgery were required in eleven out of 14 patients. Initial misdiagnosis was common, leading to delayed diagnosis and multiple courses of ineffective antibiotics. Definite treatment included fluoroquinolones or doxycycline, and led to resolution of symptoms in most patients. The varied clinical manifestations of tularemia, from classic (ulcero-)glandular forms to severe and atypical presentations illustrate its diagnostic and clinical complexity. Enhanced awareness and early consideration are crucial, especially in endemic areas or patients with anamnestic environmental exposures.