Early recognition and antibiotic therapy improve the prognosis of bacterial infections. Triage temperature in the Emergency department (ED) constitutes a diagnostic and prognostic marker of infection. The objective of this study was to assess the prevalence of community-acquired bacterial infections and the diagnostic ability of conventional biological markers in patients presenting to the ED with hypothermia.

We conducted a retrospective single-center study over a 1-year period before the COVID-19 pandemic. Consecutive adult patients admitted to the ED with hypothermia (body temperature < 36.0 °C) were eligible. Patients with evident cause of hypothermia and patients with viral infections were excluded. Diagnosis of infection was based on the presence of at least two among the three following pre-defined criteria: (i) the presence of a potential source of infection, (ii) microbiology data, and (iii) patient outcome under antibiotic therapy. The association between traditional biomarkers (white blood cells, lymphocytes, C-reactive protein [CRP], Neutrophil to Lymphocyte Count Ratio [NLCR]) and underlying bacterial infections was evaluated using a univariate and a multivariate (logistic regression) analysis. Receiver operating characteristic curves were built to determine threshold values yielding the best sensitivity and specificity for each biomarker.

Of 490 patients admitted to the ED with hypothermia during the study period, 281 were excluded for circumstantial or viral origin, and 209 were finally studied (108 men; mean age: 73 ± 17 years). A bacterial infection was diagnosed in 59 patients (28%) and was mostly related to Gram-negative microorganisms (68%). The area under the curve (AUC) for the CRP level was 0.82 with a confidence interval (CI) ranging from 0.75 to 0.89. The AUC for the leukocyte, neutrophil and lymphocyte counts were 0.54 (CI: 0.45–0.64), 0.58 (CI: 0.48–0.68) and 0.74 (CI: 0.66–0.82), respectively. The AUC of NLCR and quick Sequential Organ Failure Assessment (qSOFA) reached 0.70 (CI: 0.61–0.79) and 0.61 (CI: 0.52–0.70), respectively. In the multivariate analysis, CRP ≥ 50 mg/L (OR: 9.39; 95% CI: 3.91–24.14; p < 0.01) and a NLCR ≥10 (OR: 2.73; 95% CI: 1.20–6.12; p = 0.02) were identified as independent variables associated with the diagnosis of underlying bacterial infection.

Community-acquired bacterial infections represent one third of diagnoses in an unselected population presenting to the ED with unexplained hypothermia. CRP level and NLCR appear useful for the diagnosis of causative bacterial infection.