What is the difference between a virus and a bacterium?

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1. 1

   Diagnostic Test Accuracy of a 2-Transcript Host RNA Signature for Discriminating Bacterial vs Viral Infection in Febrile Children

   JAMA (Herberg et al.)Published Aug 23, 2016Checked Oct 11, 2026

   “The discovery group of 240 children (median age, 19 months; 62% male) included 52 with definite bacterial infection, of whom 36 (69%) required intensive care, and 92 with definite viral infection, of whom 32 (35%) required intensive care. Ninety-six children had indeterminate infection. Analysis of RNA expression data identified a 38-transcript signature distinguishing bacterial from viral infection. A smaller (2-transcript) signature (FAM89A and IFI44L) was identified by removing highly correlated transcripts. This study provides preliminary data regarding test accuracy of a 2-transcript host RNA signature discriminating bacterial from viral infection in febrile children. Further studies are needed in diverse groups of patients to assess accuracy and clinical utility of this test in different clinical settings.”

2. 2

   Differentiation of bacterial and viral pneumonia in children

   Thorax (Virkki)Published May 1, 2002Checked Oct 11, 2026

   “A potential causative agent was found in 215 (85%) of the 254 cases. Bacterial infection was found in 71% of 137 children with alveolar infiltrates on the chest radiograph, while 72% of the 134 cases with a bacterial pneumonia had alveolar infiltrates. Half of the 77 children with solely interstitial infiltrates on the chest radiograph had evidence of bacterial infection. The proportion of patients with increased WBC or ESR did not differ between bacterial and viral pneumonias, but differences in the CRP levels of >40 mg/l, >80 mg/l, and >120 mg/l were significant although the sensitivity for detecting bacterial pneumonia was too low for use in clinical practice. Most children with alveolar pneumonia, especially those with lobar infiltrates, have laboratory evidence of a bacterial infection. Interstitial infiltrates are seen in both viral and bacterial pneumonias.”

3. 3

   Complementary Utility of Metagenomic Next-Generation Sequencing and Blood Culture for Bloodstream Infections: Insights into Pathogen-Specific Inflammatory and Coagulation Profiles.

   Infection and drug resistance (Chen et al.)Published Sep 5, 2026Checked Oct 11, 2026

   “Differences in pathogen distribution and inflammatory/coagulation biomarkers across pathogen types were analyzed. Receiver operating characteristic (ROC) curve analysis was conducted to evaluate the predictive performance of these biomarkers for viral and fungal infections.ResultsCompared with blood culture, mNGS provided additional pathogen detection, with newly identified pathogens comprising viruses (33.5%, 184/550), polymicrobial infections (34.9%, 192/550), and fungal pathogens, whereas single bacterial infections accounted for only 14.5% (80/550). Compared with bacterial infections (n=80), viral infections (n=184) were associated with significantly lower procalcitonin (PCT), C-reactive protein (CRP), and fibrinogen (FIB), but higher prognostic nutritional index (PNI) (all ppConclusionmNGS complements conventional blood culture by expanding pathogen detection in clinically selected patients, while inflammatory and coagulation biomarkers may assist early etiological assessment and support clinical assessment and antimicrobial decision-making.”

4. 4

   Complete Blood Count-Derived Inflammatory Markers in Pediatric Lower Respiratory Tract Infection: A Narrative Review.

   Pathogens (Basel, Switzerland) (Joan et al.)Published Sep 8, 2026Checked Oct 11, 2026

   “s the most investigated marker, with the broadest evidence base for severity assessment and for separating bacterial from viral disease, although its performance remained pathogen-, population-, and endpoint-dependent; it was elevated in severe pertussis, tuberculosis, Mycoplasma pneumoniae, Streptococcus pneumoniae, and SARS-CoV-2 infection, whereas findings in respiratory syncytial virus infection were conflicting. The platelet-to-lymphocyte ratio had the next broadest evidence base for severity, and the systemic immune-inflammation index was consistently elevated in Mycoplasma pneumoniae and SARS-CoV-2 infection. No single ratio performed consistently across all etiologies. Ratios governed by one dominant immunopathogenic mechanism behaved predictably; those whose numerator and denominator respond to the same process did not. Cut-offs were neither standardized, age-specific, nor externally validated, and most estimates derived from retrospective cohorts in few countries; reported values therefore represent association and discrimination rather than validated prediction. Standardized, age-specific thresholds are needed before these markers can support routine risk stratification.”

5. 5

   Serious Bacterial Infections in Young Infants With Viral Infections

   AAP Grand RoundsPublished Feb 1, 2026Checked Oct 11, 2026

   “Regardless of viral test results, 93% of SBI cases had abnormal inflammatory markers or urinalysis. Additionally, SBI occurred in both virus-positive and virus-negative infants. Thus, for its cost, comprehensive viral testing is not helpful in discriminating which FYI has SBI compared with inflammatory markers.The current study has several limitations. The first is its retrospective design, which left investigators unblinded to the final SBI status and introduced bias during data collection and analysis. The second is that the researchers focused only on hospitalized FYI, limiting generalizability to settings where older infants often are managed as outpatients. Finally, the overall sample size, particularly the number of infants with invasive bacterial infection and for specific viral subgroups (eg, adenovirus, coronaviruses, metapneumovirus), was limited, reducing statistical power for subgroup analyses.Comprehensive viral testing is not associated with improved risk stratification and is more expensive than inflammatory markers and urinalysis for excluding SBI in FYI. Targeted testing may be a more resource-efficient strategy for this population.”