Sample collection is a critical step in diagnosing viral diseases, as it ensures accurate detection of the virus or viral antigens in affected individuals. Proper sample collection depends on the suspected virus, the clinical symptoms, and the target organ system.
General Guidelines for Viral Sample Collection
- Timing: Samples should be collected as early as possible after symptom onset, when viral load is highest.
- Sterility: Use sterile equipment and containers to avoid contamination.
- Transport: Use viral transport media (VTM) and maintain samples at appropriate temperatures, typically 2-8°C if processing is delayed.
- Documentation: Proper labeling and completion of laboratory request forms are essential.
Types of Samples and Their Collection Methods
1. Respiratory Viruses (e.g., Influenza, COVID-19, RSV)
- Sample Types: Nasopharyngeal swabs, throat swabs, nasal aspirates, sputum, bronchoalveolar lavage.
- Method:
- For nasopharyngeal swabs, insert a flexible swab into one nostril, parallel to the palate, until resistance is felt, then gently rotate.
- Sputum: Collected from deep coughing into a sterile container.
- Transport: Use VTM, refrigerate, and transport to the lab within 48 hours.
2. Gastrointestinal Viruses (e.g., Rotavirus, Norovirus)
- Sample Types: Stool, rectal swabs, vomitus.
- Method:
- Stool: Collect in a sterile, leak-proof container. Avoid contamination with urine.
- Rectal swab: Insert the swab into the rectum and rotate gently.
- Transport: No special transport media required for stool. Keep at 2-8°C if delayed.
3. Blood-borne Viruses (e.g., HIV, Hepatitis B/C, Dengue, Zika)
- Sample Types: Whole blood, serum, plasma.
- Method:
- Use sterile syringes to collect venous blood into tubes. For serology, collect in tubes without anticoagulant; for PCR, use EDTA or citrate tubes.
- Transport: Keep at 2-8°C or freeze for long-term storage.
4. Skin and Mucocutaneous Lesions (e.g., Herpes Simplex Virus, Varicella-Zoster Virus)
- Sample Types: Vesicular fluid, lesion swabs, biopsy.
- Method:
- For vesicular fluid, puncture the vesicle and collect the fluid with a swab.
- For biopsy, obtain a small skin sample using sterile techniques.
- Transport: Use VTM or saline, and refrigerate.
5. Central Nervous System (CNS) Viruses (e.g., Enteroviruses, Herpesviruses, Rabies)
- Sample Types: Cerebrospinal fluid (CSF), brain tissue (for post-mortem diagnosis).
- Method:
- CSF: Obtain via lumbar puncture using aseptic techniques.
- Transport: Keep at 2-8°C, ideally process within a few hours.
6. Genital Viruses (e.g., Human Papillomavirus, Herpes Simplex Virus)
- Sample Types: Genital swabs, urethral swabs, cervical swabs.
- Method:
- Swabs should be collected from the cervix or urethra using sterile swabs.
- Transport: Use VTM and refrigerate if not processed immediately.
7. Ocular Viruses (e.g., Adenovirus, Herpesviruses)
- Sample Types: Conjunctival swabs, corneal scrapings.
- Method:
- Swab the lower conjunctival sac or scrape corneal lesions with a sterile instrument.
- Transport: Use VTM, store at 2-8°C.
8. Zoonotic Viruses (e.g., Rabies, Ebola)
- Sample Types: Blood, CSF, saliva, brain tissue (post-mortem).
- Method:
- Saliva: Collected with a sterile swab from the oral cavity.
- Brain tissue: Collected during necropsy following biosafety protocols.
- Transport: Use appropriate containment and transport media, refrigerate or freeze.
Special Considerations
- Biosafety: Samples from highly infectious diseases like Ebola or Hantavirus should be handled in high-containment labs (BSL-3/4).
- Preservation: If immediate processing is not possible, samples may need to be stored at -80°C to preserve viral integrity.