What cell lines are used for viral culture in suspected respiratory virus infection?

Cell Lines for Viral Culture in Suspected Influenza Infection

For suspected influenza infection in a 4-year-old with respiratory symptoms, the sputum specimen should be processed for viral culture using MDCK (Madin-Darby Canine Kidney) cells for influenza viruses, LLC-MK2 cells for parainfluenza viruses, and HEp-2 cells for respiratory syncytial virus (RSV).

Rationale for Cell Line Selection

Viral culture remains an important diagnostic method for respiratory viruses, particularly when molecular testing is not immediately available or when a viable isolate is needed. The choice of cell lines is critical for optimal virus isolation.

Specific Cell Lines for Respiratory Viruses

1. MDCK cells:

   • Primary cell line for influenza virus isolation 1
   • Provides optimal growth conditions for influenza A and B viruses
   • Essential given the patient's presentation with fever, cough, and respiratory symptoms during winter months

2. LLC-MK2 cells:

   • Optimal for parainfluenza virus isolation 1, 2
   • Important to include as parainfluenza can present with similar symptoms

3. HEp-2 cells:

   • Highly effective for RSV isolation 2
   • Critical consideration in a 4-year-old with respiratory symptoms

Combined Cell Line Approach

A shell vial assay using simultaneous culture of multiple cell lines (HEp-2, LLC-MK2, and MDCK) in a single vial (CoHLM SV assay) can detect 94.1% of respiratory viral strains within 48 hours, compared to traditional tube culture which takes approximately 6 days 2. This approach is particularly valuable for rapid diagnosis in a pediatric patient with significant respiratory symptoms.

Clinical Context and Specimen Collection

The patient's clinical presentation strongly suggests a viral respiratory infection:

• 5-day history of fever, headache, nonproductive cough
• Nasal congestion and shortness of breath
• Physical exam showing fever (39°C), increased respiratory rate (35/min), and rales at the base of right lung
• Chest X-ray revealing right lower lobe infiltrate

These findings, occurring in January (peak respiratory virus season), are highly consistent with influenza or other respiratory viral infections.

Additional Considerations

Timing of Specimen Collection

• The specimen was collected early in the course of illness (within 5 days of symptom onset), which is optimal for viral culture

Alternative Testing Methods

While viral culture remains valuable, nucleic acid amplification testing (NAT) has become the reference standard for respiratory virus detection due to:

• Higher sensitivity
• Faster turnaround time (typically <24 hours)
• Ability to detect multiple viruses simultaneously 3

Common Pitfalls to Avoid

1. Inadequate specimen collection: Ensure proper collection of induced sputum with minimal contamination

2. Delayed processing: Respiratory specimens should be transported promptly to the laboratory in appropriate viral transport media to maintain virus viability

3. Using limited cell lines: Using only a single cell line may miss important respiratory pathogens, as different viruses grow preferentially in different cell lines 4

4. Failure to consider epidemiological context: The timing (January) increases the likelihood of influenza and RSV

By using the appropriate combination of cell lines (MDCK, LLC-MK2, and HEp-2), the laboratory can optimize detection of the most common respiratory viruses causing illness in this pediatric patient with significant respiratory symptoms.