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In infants <3 months old, or in immunodepressed patients, untreated minor Salmonella infections may be associated with metastatic localization to bone, lung, meninges and ear12; these patients are usually treated with antibiotics. Unfortunately clinical data or laboratory tests (including search for occult blood or leukocytes in stools13 are often inaccurate in differentiating bacterial from viral gastroenteritis (GE); only culture allows a reliable diagnosis.
The diagnostic accuracy of C-reactive protein (CRP), erythrocyte sedimentation rate (ESR) and white blood cell (WBC) count and their usefulness in the clinical differentiation of viral from bacterial GE in children have been investigated in a recent paper by Borgnolo et al.14
We have tried to confirm the data obtained by Borgnolo et al.14 in a group of 248 consecutive children with acute GE admitted to our pediatric department.
Methods. From January, 1996, to June, 1998, 260 children were admitted to our pediatric department for acute GE. A rectal swab culture was performed in 247 children for bacterial culture of Salmonella and Shigella spp., with standard laboratory techniques. Rotavirus and adenovirus were searched for using the rapid latex tests Rotalatex and Adenolatex (Bouty, Milan, Italy).
At the time of admission we also determined CRP concentration (standard nephelometric method), ESR (standard Westergren method) and WBC count (using a standard automated cell counter).
Maximal body temperature, age, days of hospitalization, days with diarrhea, presence of vomiting and need for parenteral rehydration were also recorded.
Statistical analysis was performed with standard computer software (Microsoft Excel and SPSS 6.0 for Windows). Receiver operating characteristic curve analysis was performed with GraphRoc for Windows 2.0.
Results. Of 247 children admitted with acute GE, 29 (11.7%) had a confirmed bacterial infection (all minor Salmonella spp.), 121 (48.9%) had a confirmed viral infection (90 rotavirus, 8 adenovirus, 23 rotavirus and adenovirus combined), and 97 (39.3%) had no demonstrable pathogen.
For analysis of the positive and negative predictive values, we pooled the data of the patients with viral and undetermined GE, given the impossibility of distinguishing clinically between the two conditions.
The receiver operating characteristic (ROC) curve of CRP, ESR and WBC are shown in Figure 1; the area under the ROC curve was 0.8674 for CRP, 0.7575 for ESR and 0.4963 for WBC count (a test with no power of discrimination has an area under the curve of 0.5000). The differences between the three ROC curves are significant (CRP vs. ESR, P = 0.03; CRP vs. WBC, P < 0.0001; ESR vs. WBC, P < 0.001).
CRP was equal or higher than 2 mg/dl in 24 of 29 (82.7%) children with Salmonella infection, in 21 of 121 (17.3%) children with a viral infection and in 22 of 97 (22.7%) children with no identifiable pathogen.
With a value of 2.0 or greater, the sensitivity of CRP was 79.3%, with a specificity of 80.3%; the positive predictive value (i.e. the percentage of children with a CRP ≥2.0 who are expected to have a Salmonella GE) is 34.8%, whereas the negative predictive value (i.e. the percentage of children with a CRP <2.0 who are not expected to have Salmonella GE) was 96.7%. A summary of the efficiency data with thresholds of 1.2, 2.0 and 3.5 mg/dl is reported in Table 1.
