BacteriologyValue of serum procalcitonin, neopterin, and C-reactive protein in differentiating bacterial from viral etiologies in patients presenting with lower respiratory tract infections
Introduction
Lower respiratory tract infections (LRTIs) account for a 6.9% global mortality (World Health Report, WHO 2004), drain already stretched health care resources, and can bring down a country's health service and economy. Differentiating viral from bacterial causes of LRTI is important so that, first, optimal treatment is started, second, inappropriate antibiotic treatment and subsequent resistance is prevented, and third, patients with mixed infection are not cohorted together.
Antibiotic resistance is a global concern, and strategies that use biomarkers to delineate bacterial from viral etiologies have been applied to aid more judicious use of antibiotics. Serum procalcitonin (PCT) is a marker of bacterial infection (Simon et al., 2004), and a newly developed assay (Kryptor PCT; BRAHMS, Hennigsdorf, Germany) has been introduced and used to guide the appropriate use of antibiotics in patients with LRTIs (Christ-Crain et al., 2004) and community-acquired pneumonia (CAP) (Christ-Crain et al., 2006). Prompt initiation of appropriate antibiotic therapy improves outcome, and a delay of more than 4 h in bacterial CAP has been associated with increased mortality (Meehan et al., 1997). The potential use of biomarker(s) to accurately include or exclude bacterial and viral infection will improve the management of LRTI.
In this study, we evaluated assays for PCT, neopterin, and C-reactive protein (CRP) alone and in combination to differentiate bacterial from viral causes of LRTI.
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Patient subjects
Ethical approval was obtained to conduct a prospective study of consecutive patients admitted to the Prince of Wales Hospital (PWH), Hong Kong, through our emergency department with LRTI/CAP between January 1 and December 31, 2004. Sera were obtained from all patients on the day of hospitalization for suspected LRTI and were used for the evaluation of 3 markers: PCT, neopterin, and CRP. PWH is a 1350-bed teaching hospital and tertiary referral center for the New Territories of the Hong Kong
Patient characteristics
The mean age of the patients with LRTI in the 2 groups with bacterial and viral etiology was both 69.7 years (the range for the 2 groups was 20–103 years and 15–91 years, respectively), and the female-to-male ratio was 1:1.15. In thecontrol group, the mean age was 61.9 years (range, 19–91 years) with a female-to-male ratio of 3.1:1.
CRP, neopterin, and PCT levels
In patients with LRTI of bacterial etiology, serum CRPconcentrations were raised above the normal range (>10 mg/L) in 132 (95%) of 139 patients compared with 6
Discussion
This study shows that CRP >10 and PCT >0.1 may be used to rule in bacterial infection in 60% to 95% cases of bacterial infection, whereas neopterin >10 may be used to rule in viral infection in 97% cases. PCT is a reliable marker of sepsis as applied in the intensive care setting (Müller et al., 2000), and PCT has been shown to be sensitive and specific for differentiating bacterial from viral etiology in children admitted with CAP (Moulin et al., 2001). However, in adults with CAP, PCT was
Acknowledgment
The authors thank the Research Department of BRAHMS, Hennigsdorf, Berlin, and in.vent diagnostica, Hennigsdorf, Berlin, for donation of Neopterin ELISA kits and Kryptor PCT®. This study was supported in part by the Small Entrepreneur Research Assistance Programme (SERAP, S/P895/05B), and by Dr. George W.H. Cautherley of R&C Biogenius, Hong Kong.
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