UMass Chan Medical School Faculty Publications


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

UMMS Affiliation

Department of Emergency Medicine; Department of Medicine, Division of Infectious Diseases and Immunology

Publication Date


Document Type



Adolescent; Adult; Aged; Analysis of Variance; Bacterial Infections; Biological Markers; C-Reactive Protein; Female; Humans; Influenza, Human; Male; Middle Aged; Predictive Value of Tests; Prospective Studies; ROC Curve; Sensitivity and Specificity; Trauma Centers; Virus Diseases


Bacterial Infections and Mycoses | Diagnosis | Emergency Medicine | Immunology and Infectious Disease | Infectious Disease | Influenza Humans


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 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.

DOI of Published Version



Am J Emerg Med. 2013 Jan;31(1):137-44. doi: 10.1016/j.ajem.2012.06.026. Link to article on publisher's site

Related Resources

Link to Article in PubMed

Journal/Book/Conference Title

The American journal of emergency medicine

PubMed ID