Overview
RNA viruses of medical importance include influenza and other respiratory agents, enteroviruses, norovirus, coronaviruses, flaviviruses, and retroviruses such as HIV. Clinical laboratories detect them primarily with NAAT, selected antigen assays, and serology/RNA algorithms for blood-borne infection.
Classification
| Family / group | Examples | Typical lab emphasis |
|---|---|---|
| Orthomyxoviridae | Influenza A/B | Antigen ± NAAT |
| Pneumoviridae / Paramyxoviridae | RSV, measles, mumps | NAAT; serology as indicated |
| Picornaviridae | Enterovirus, rhinovirus | NAAT from appropriate site |
| Coronaviridae | SARS-CoV-2, seasonal CoV | NAAT ± antigen |
| Caliciviridae | Norovirus | Stool NAAT/antigen |
| Retroviridae | HIV | Ag/Ab ± RNA algorithms |
| Flaviviridae | HCV, arboviruses | Serology ± RNA/PCR |
Morphologic Features
Routine light microscopy does not identify RNA virions. Laboratory appearance is assay signal; some enveloped RNA viruses are relatively labile as infectious particles outside the host.
Laboratory Characteristics
- Respiratory multiplex panels list discrete RNA (and sometimes DNA) targets
- Rapid antigen devices prioritize turnaround with sensitivity tradeoffs
- HIV/HCV pathways follow multi-step laboratory algorithms
- Arbovirus testing is often referral- or season-directed
Reference Intervals
Qualitative RNA assays use detected/not detected language with assay-specific cutoffs. Quantitative HIV/HCV RNA uses IU/mL or copies/mL per method; interpretive and critical thresholds are institutional, verify locally.
| Result type | Meaning | Notes |
|---|---|---|
| Antigen not detected | Below antigen assay cutoff | May need NAAT per protocol |
| RNA detected | Nucleic acid present | Target- and specimen-scoped |
| Ab screen reactive | Needs algorithm confirmation | Do not finalize from screen alone if SOP requires more |
| RNA viral load | Quantified RNA | Method-specific units |
Clinical and Laboratory Significance
Significance depends on syndrome timing, specimen quality, and assay class. Co-detections on multiplex panels require clinical correlation; blood-borne RNA confirms active viremia/infection state within algorithm rules.
Differential Considerations
Differentiate true negatives from early/late antigen misses, degraded RNA, inhibitors, and unlisted pathogens outside panel scope.
Comparison Tables
Antigen vs NAAT (RNA viruses)
| Feature | Rapid antigen | Molecular NAAT |
|---|---|---|
| Typical speed | Minutes–hours | Hours (method-dependent) |
| Analytical sensitivity | Often lower | Often higher |
| Best use framing | Rapid screen when validated | Confirmation / broader panels |
Classification Frameworks
Family taxonomy follows ICTV. Public-health case definitions for influenza, COVID-19, HIV, and others are separate operational frameworks that may incorporate laboratory criteria.
Laboratory Notes
- Enforce transport times for RNA specimens per SOP
- Hedge screening cutoffs and confirmation algorithms as local/current
- Read multiplex target lists before counseling “virus ruled out”
References
Authoritative textbooks, guidelines, and reviews supporting this reference entry. Verify reference intervals, critical limits, and reflex criteria against institutional protocols and current guideline editions.
Textbooks
- Forbes BA, Sahm DF, Weissfeld AS. Bailey & Scott's Diagnostic Microbiology. 15th ed. Elsevier; 2020.
- Mahon CR, Lehman DC, Manuselis G. Textbook of Diagnostic Microbiology. 6th ed. Elsevier; 2018.
- Carroll KC, Hobden JA, Miller S, et al. Jawetz, Melnick, & Adelberg's Medical Microbiology. 28th ed. McGraw-Hill; 2019.
- Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology. 9th ed. Elsevier; 2021.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial Susceptibility Testing. CLSI document M100 (verify current edition and institutional adoption).
- Centers for Disease Control and Prevention / NIH. Biosafety in Microbiological and Biomedical Laboratories (BMBL). Current edition (verify institutional adoption).
Frequently Asked Questions
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