Identifying the Probable Etiology of Acute Undifferentiated Fever through Inflammatory Markers.

ABSTRACT

BACKGROUND: Acute undifferentiated fever (AUF) is defined as any febrile illness with a duration of ≤14 days without evidence of localized infection. Most outpatient services and a significant inpatient load in India are contributed by AUF. COVID-19 has recently added to the existing list of common etiologies of AUF. While the rapid diagnostic test (RDT) kits, which are widely used for the detection of common etiologies of AUF, are unreliable, the rise of various inflammatory markers may help identify the probable etiology. This not only results in better diagnosis but also prepares the physician for close monitoring and pooling of resources. AIM: To identify the probable etiology of AUF through inflammatory markers. OBJECTIVE: To understand the clinical and biochemical parameters as possible predictors of adverse outcomes in AUF. MATERIALS AND METHODS: This was a prospective observational study carried out in the Department of Medicine in a tertiary care hospital. The total duration of the study was 1 year. A total of 400 AUF patients [both outpatient department (OPD) and inpatient department (IPD)] fulfilling the eligibility criteria were taken up for the study after consent. Various inflammatory markers, namely erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), D-dimer, ferritin, and procalcitonin levels along with basic blood and biochemical tests were measured in all qualifying patients at their first visit. The level of rise of all the measured inflammatory markers was analyzed for clues toward identifying the etiology. Also, the possible predictors of adverse outcomes, as defined in the study, were analyzed. Outcome variables are described as mean ± standard deviation. All statistical calculations were done using computer programs Microsoft Excel 2007 (Microsoft Corporation, New York, United States of America) and SPSS (Statistical Product and Service Solutions; SPSS Inc., United States of America) version 21. RESULTS: The common etiologies in our study contributing to AUF were dengue (31.5%), COVID-19 (18.5%), enteric fever (12.7%), scrub typhus (9.0%), and malaria (6.0%). In 76 cases (19%), the fever was undiagnosed. Enteric fever had highly elevated CRP (>30 mg/L) and moderately elevated D-dimer, ferritin, and procalcitonin. Both nonsevere dengue and COVID-19 had highly elevated D-dimer (>750 ng/mL), but in nonsevere dengue, CRP, ferritin, and procalcitonin were only mildly elevated, whereas in COVID-19, CRP and ferritin were moderately elevated with mildly elevated procalcitonin. Scrub typhus had highly elevated CRP and ferritin [more than four times the upper limit of normal (ULN)], but D-dimer and procalcitonin were only mildly elevated. The mean serum procalcitonin level in enteric fever is significantly higher than the other etiologies of AUF. Our study was correctly able to identify 90.8% of nonsevere dengue, 87.8% of typhoid, 83.6% of COVID-19, and 91.4% of scrub typhus patients based on the inflammatory markers level. Obesity, diabetes (both types 1 and 2), hypertension, coronary artery disease (CAD), malignancy, chronic kidney disease (CKD), and chronic lung disease were significantly associated with adverse outcomes. A significant delay in visiting the hospital after the onset of fever was found in all etiologies of AUF, which had adverse outcomes. CONCLUSION: Our study is one of the few studies comparing the rise in the level of various inflammatory markers among the common etiologies of AUF. The novelty of the study is that it aids in identifying the probable etiology of AUF with good confidence through the levels of inflammatory markers. Also, our study highlights the high-risk factors associated with adverse outcomes in AUF.