C-reactive protein as predictor of bacterial infection among patients with an influenza-like illness

John Patrick Haran; Francesca Lynn Beaudoin; Selim Suner; Shan Lu

doi:10.1016/j.ajem.2012.06.026

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C-reactive protein as predictor of bacterial infection among patients with an influenza-like illness☆☆☆★

John Patrick Haran, MD

Francesca Lynn Beaudoin, MD, MS

Selim Suner, MD

Shan Lu, MD, PhD

DOI: http://dx.doi.org/10.1016/j.ajem.2012.06.026

Article Info

Fig. 1

Box-and-whisker diagram of the 3 groups for CRP values in mg/L. The top and bottom of the gray boxes depicts the 75th and 25th percentile of the data with band near the middle being the 50th (median) percentile with the numerical value of the median depicted next to the plot. The upper bar line represents the 98th and the lower bar line represents the 2nd percentile.

Fig. 2

The ROC curve plot of the sensitivity of C-reactive protein as a test identifying for bacterial infection. The hashed lines represent the 95% upper and lower confidence intervals (CI) and the solid line is the true-positive fraction (TPF).

Fig. 3

The sensitivity of CRP at decreasing 10 mg/L intervals starting from 80 mg/L. The arrows are the average with the black line running from the 95% upper and lower confidence intervals. The average approaches 100% sensitivity at 20 mg/L.

Fig. 4

The ROC curve plot of the sensitivity of CRP, WBC count, percentage segmented neutrophils (Segs) and percentage banded neutrophils (Bands) as tests to identify bacterial infection.

Abstract

Objective

During the influenza season patients are labeled as having an influenza-like illness (ILI) which may be either a viral or bacterial infection. We hypothesize that C-reactive protein (CRP) levels among patients with ILI diagnosed with a bacterial infection will be higher than patients diagnosed with an influenza or another viral infection.

Methods

We enrolled a convenience sample of adults with ILI presenting to an urban academic emergency department from October to March during the 2008 to 2011 influenza seasons. Subjects had nasal aspirates for viral testing, and serum CRP. Bacterial infection was determined by positive blood cultures, radiographic evidence of pneumonia, or a discharge diagnosis of bacterial infection. Receiver operating characteristic curve, analysis of variance, and Student t test were used to analyze results.

Results

Over 3 influenza seasons there were 131 total patients analyzed (48 influenza infection, 42 other viral infection and 41 bacterial infection). CRP values were 25.65 mg/L (95% CI, 18.88-32.41) for influenza, 18.73 mg/L (95% CI, 12.97-24.49) for viral and 135.96 mg/L (95% CI, 99.38-172.54) for bacterial. There was a significant difference between the bacterial group, and both the influenza and other viral infection groups (P < .001). The receiver operating characteristic curve for CRP as a determinant of bacterial infection had an area under the curve of 0.978, whereby a CRP value of <20 had a sensitivity of 100% and >80 had a specificity of 100%.

Conclusion

C-reactive protein is both a sensitive and specific marker for bacterial infection in patients presenting with ILI during the influenza season.

☆Funding: This study was designed and carried out at Rhode Island Hospital/Brown University and was supported by an intradepartmental grant through the Department of Emergency Medicine.

☆☆Meetings: Presented at the Society for Academic Emergency Medicine (SAEM) Annual Meeting, Boston, MA, June 6, 2011 (Lightning Oral Presentation) Academic Emergency Medicine, Volume 18, number 5, p s141, May 2001.

★Presented at SAEM New England Emergency Medicine Research Directors (NERDS) Regional Meeting, Worcester, MA, April 6, 2011 (Oral Presentation).

C-reactive protein as predictor of bacterial infection among patients with an influenza-like illness☆☆☆★

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