Should co‑infections be considered in patients with a positive enterovirus test, given that about 45% have co‑infection, especially with adenovirus?

Co-infections Must Be Actively Sought in Enterovirus-Positive Patients

Yes, co-infections should be systematically considered and tested for in patients with positive enterovirus results, as nearly half of EV-positive cases harbor additional pathogens, most commonly adenovirus. This high co-infection rate has direct implications for clinical management, interpretation of symptoms, and infection control measures.

The Evidence for High Co-infection Rates

The most recent data demonstrates that 45.7% of enterovirus-positive respiratory samples contained co-infections, with adenovirus being the predominant co-pathogen (38.0%), followed by Mycoplasma pneumoniae (8.1%) 1. This finding is particularly relevant in pediatric populations, where the youngest children (0-4 years) show the highest rates of both EV detection and co-infection 1.

Additional studies confirm this pattern across different clinical contexts:

• In primary care settings with acute respiratory infections, co-infections occurred in 28.2% of cases, though notably adenovirus co-infected with nearly all other respiratory viruses tested 2
• In gastroenteritis surveillance, 5.4% of samples showed HAdV and enterovirus co-detection 3
• Rhinovirus/enterovirus co-infections with RSV and adenovirus occurred in 21.4% of bronchiolitis cases 4

Clinical Implications and Testing Strategy

When to Suspect and Test for Co-infections

Multiplex respiratory panel testing should be standard practice for EV-positive patients presenting with:

• Neurological symptoms (meningitis, encephalitis, acute flaccid myelitis)
• Severe respiratory disease
• Neonatal sepsis
• Any hospitalized pediatric patient
• Immunocompromised individuals

The European guidelines explicitly recommend collecting multiple specimen types simultaneously: CSF, stool, AND respiratory samples for neurological presentations; respiratory samples are mandatory even when CSF is the primary concern 5.

Age-Specific Considerations

Children under 5 years require heightened vigilance, as they demonstrate:

• The highest EV detection rates (84.6% of all EV cases in children ≤17 years) 1
• Greater likelihood of co-infection, particularly in the youngest age groups 1, 6
• More severe clinical presentations when co-infected with specific viral combinations

Specific Viral Pairings That Matter

Not all co-infections carry equal clinical weight. RSV-containing combinations with adenovirus or rhinovirus are associated with increased respiratory burden 7. However, some rhinovirus-associated combinations may represent viral interference rather than true pathogenic co-infection 7.

Critical Pitfalls to Avoid

The Colonization vs. Infection Dilemma

Enteroviruses colonize the throat and gut for weeks to months; detection in these sites must be interpreted cautiously 5. This is particularly problematic when:

• Respiratory or stool samples are positive but CSF is negative in neurological cases
• Symptoms have resolved but viral shedding continues
• Asymptomatic contacts test positive

Solution: Correlate molecular findings with:

• Viral load (higher loads suggest active infection)
• Sample timing relative to symptom onset
• Clinical presentation severity
• Presence of other pathogens

The EV-D68 Exception

For acute flaccid myelitis or paralysis cases, respiratory specimens are mandatory because EV-D68 is rarely detectable in CSF or stool 5. Missing this requires testing only CSF would result in false-negative results for a critical pathogen.

Multiplex PCR Interpretation

The increased sensitivity of multiplex molecular assays detects viral nucleic acid, not necessarily viable virus. Clinical impact depends more on specific viral pairings and host factors than on the number of detected viruses 7. A positive result requires integration with:

• Clinical severity
• Laboratory markers (pleocytosis, inflammatory markers)
• Radiological findings
• Patient age and immune status

Practical Testing Algorithm

1. Initial EV-positive result → Automatically reflex to multiplex respiratory panel if not already performed
2. Collect multiple specimen types based on clinical presentation (per guideline recommendations 5)
3. Prioritize testing for:
   • Adenovirus (most common co-pathogen)
   • RSV (in respiratory presentations)
   • Human parechovirus (in neonates and young infants with negative EV testing)
4. Interpret results in context:
   • High viral loads + acute symptoms = likely pathogenic
   • Low loads + prolonged detection = possible colonization
   • Specific high-risk combinations (RSV+adenovirus, RSV+HMPV) = increased clinical concern

Seasonal and Epidemiological Context

EV circulates year-round, but co-infection patterns vary seasonally: single infections peak in autumn while co-infections predominate in spring 1. This temporal variation should inform testing strategies and infection control measures during different seasons.

The post-pandemic period has re-established endemic circulation of multiple respiratory viruses simultaneously 2, making co-infection surveillance increasingly important for both individual patient management and public health monitoring.