Evaluating the Diagnostic Value of Absolute Eosinopenia in Culture-Positive Enteric Fever: A Retrospective Case-Control Study.

Background Enteric fever continues to pose a diagnostic challenge in endemic regions due to the limited availability and delayed results of blood cultures and the poor specificity of serological tests. Absolute eosinophil count (AEC = 0 cells/mm³), a simple and low-cost hematological marker, may offer early diagnostic utility, especially in resource-constrained settings. Objective To evaluate the diagnostic performance of absolute eosinopenia in detecting culture-confirmed enteric fever and compare it with commonly used serological tests such as Widal and Typhidot. Methods This retrospective case-control study was conducted at a tertiary care teaching hospital in eastern India between August 2023 and June 2024. Culture-positive patients with Salmonella Typhi or S. Paratyphi were enrolled as cases, while febrile patients with confirmed non-enteric diagnoses served as controls. Data were extracted from electronic health records. A total of 159 patients (79 cases and 80 controls) were included. Sample size was calculated using prior eosinopenia proportions (59% vs. 13%), with α = 0.05 and 80% power. Absolute eosinophil counts were obtained using an automated hematology analyzer, and diagnostic accuracy was compared to serological testing. Results Absolute eosinopenia was observed in 46.8% of enteric fever cases and 8.75% of controls. It showed a sensitivity of 45.6% (95% CI: 34.3-57.3) and a specificity of 91.3% (95% CI: 82.7-96.4), with a positive predictive value of 84.6% and a negative predictive value of 61.6%. The area under the receiver operating characteristic (ROC) curve for AEC was 0.68 (95% CI: 0.60-0.76), demonstrating moderate diagnostic accuracy. These results were comparable or superior to commonly used serological tests. Conclusion Absolute eosinopenia demonstrates high specificity and moderate overall diagnostic accuracy for enteric fever. It may serve as a rapid, adjunctive marker to support clinical suspicion in endemic, resource-limited settings - particularly where blood culture or reliable serological testing is unavailable. However, it should be interpreted alongside leukocyte counts and clinical features rather than used as a standalone diagnostic criterion. Limitations As a retrospective, single-center study, findings may be influenced by selection bias and may not be generalizable across broader populations. The timing of eosinophil count measurement relative to symptom onset was not standardized. Further prospective studies are needed to validate these findings.