Low procalcitonin level in acute scrub typhus

Background: Procalcitonin (PCT) is a promising biomarker for identification of bacterial infections. In bacterial infections, serum PCT levels start to rise at 4 hours after the onset of systemic infection, and peak at between 8 and 24 hours. PCT can be used as a rapid diagnostic biomarker to differentiate between culture-negative bacterial sepsis and systemic inflammatory response syndrome. The level of PCT associated with O. tsutsugamushiinfection is rarely investigated. To the best of our knowledge, no study has focused on the usefulness of PCT for the diagnosis of acute scrub typhus.

Methods: we compared serum PCT levels of acute scrub typhus with that of Escherichia coli bacteraemia on the day of admission. In addition, we determined the optimal cutoff value of serum PCT levels for diagnosing acute scrub typhus. E. coli bacteraemia was defined as E. coli grown from blood culture taken on the day of admission. Serum PCT levels were assessed within the first 24 hours following admission. This retrospective study was conducted in Wonkwang University Hospital and Chonbuk National University Hospital in Korea between July and December 2011. A total of 106 patients (≥ 18 years old) with acute scrub typhus and 82 patients (≥ 18 years old) with E. coli bacteraemia were included in the study

Results: The mean ages of the patients with acute scrub typhus and with E. coli bacteraemia were 64.9 years and 73.3 years, respectively. The mean serum PCT levels in patients with acute scrub typhus and with E. coli bacteraemia were 0.90 ng/ml and 43.7 ng/ml, respectively. Receiver operating characteristic (ROC) curve analysis determined the optimal cutoff value of serum PCT to be 1.3 ng/ml with a sensitivity of 87.7% and a specificity of 78.0%. Patients with PCT levels lower than 1.3 ng/ml had a 25.4 times higher risk for having acute scrub typhus than for having E. coli bacteraemia (Table 1) .

Conclusion: Our study suggests that PCT levels (≤ 1.3 ng/ml) may be used to diagnose acute scrub typhus and that PCT can be used by differentiation from gram-negative bacterial infection.

Table 1. . Sensitivity, specificity, and odds ratio for acute scrub typhus according to cutoff value of procalcitonin levels.

Cutoff value of PCT level (ng/ml)	Sensitivity (%)	Specificity (%)	Odds ratio	95% Confidence interval
≤ 0.98	80.2	78.0	14.4	7.088-29.220
≤ 1.2	84.9	78.0	20.0	9.487-42.162
≤ 1.27	87.7	78.0	25.4	11.646-55.553