Background
Seroepidemiologic studies of human tularemia have been conducted throughout the northern hemisphere. The purposes of this study are (1) to provide an overview of F. tularensis seroprevalence data, and (2) to generate an estimate of the proportion of study participants whose infection remained subclinical.
Methods
We conducted a systematic review of Francisella tularensis seroprevalence studies according to the PRISMA guidelines. We searched Pubmed®, Embase® and Web of Science™covering the period from 1951 to 2023.
Results
The weighted pooled seroprevalence among 44’486 participants recruited in 52 studies was 3.7% (95% confidence interval (CI) 2.7-5.1). Reported seroprevalences ranged between 0.2% and 31.3%. Occupational activities associated with an increased likelihood of exposure (risk ratio (RR) 3.51 (3.2-3.86)) and studies from North America vs. Europe and Asia (4.53 (4.15-4.94)) were associated with significantly increased seropositive rates. Twenty-eight datasets (47%) reported clinical information on a total of 965 seropositive participants. The weighted pooled estimate for subclinical seropositivity was 84.4% (95% CI 72.9-991.7). Studies from F. tularensis type A areas (RR 0.37, 95% CI 0.27-0.51) and studies from sites where pulmonary tularemia prevailed (RR 0.38, 95% CI 0.28-0.51) reported lower subclinical seropositivity rates than studies from type B areas and from areas of predominance of (ulcero-) glandular or oropharyngeal tularemia, respectively.
Conclusions
Throughout the northern hemisphere, only a small proportion of study participants showed serologic evidence of exposure to F. tularensis. Eight outof 10 seropositive participants had no historical evidence of past clinical tularemia.