Can Upper Respiratory Tract Infections (URTI) be caused by influenza?

Upper Respiratory Tract Infections Can Be Caused by Influenza Virus

Yes, upper respiratory tract infections (URTIs) can definitely be caused by influenza virus. 1 Influenza is one of the common viral etiologies of URTIs, which involve infection of the nose, sinuses, pharynx, and larynx.

Influenza as a Cause of URTI

• Influenza virus is a major respiratory pathogen that commonly causes upper respiratory tract infections, presenting with symptoms such as cough, sore throat, nasal congestion, and coryza (runny nose) 1
• The common cold syndrome, which is primarily an upper respiratory tract infection, can be caused by several viruses including influenza, rhinoviruses, coronaviruses, parainfluenza viruses, respiratory syncytial virus, adenoviruses, and enteroviruses 1
• Influenza viruses (both A and B types) are frequently detected in upper respiratory specimens from patients with respiratory symptoms 2, 3

Clinical Manifestations of Influenza URTI

• Typical symptoms of influenza-related URTI include:

  • Cough
  • Sore throat
  • Nasal congestion
  • Coryza (runny nose)
  • Fever (often higher than in other viral URTIs)
  • Systemic symptoms such as myalgia, headache, fatigue, and malaise 1, 4

• The diagnosis of influenza-related URTI is typically made based on clinical presentation during influenza season, with laboratory confirmation available through various methods:

  • Nucleic acid testing (NAT)
  • Direct antigen detection (DAD)
  • Virus isolation by cell culture (VIC) 1

Relationship Between URTI and LRTI with Influenza

• Influenza infection often begins as an URTI but can progress to lower respiratory tract infection (LRTI) in some cases 5
• Higher viral burden (as measured by lower cycle threshold values in PCR testing) during influenza URTI has been associated with increased risk of progression to LRTI, particularly in immunocompromised patients 5
• In children, influenza-associated acute otitis media (AOM) occurs in up to two-thirds of young children with influenza virus infection, typically developing 2-5 days after URTI onset 1

Treatment Considerations for Influenza URTI

• Neuraminidase inhibitors (NAIs) such as oseltamivir and zanamivir are FDA-approved for treatment of acute uncomplicated influenza 4, 6
• Early administration of antivirals during uncomplicated URTI may prevent progression to complications like AOM, with studies showing a reduction in the development of AOM by 43-85% in young children treated with oseltamivir within 12-48 hours of influenza symptom onset 1
• The recommended dose of oseltamivir for treatment of influenza in adults and adolescents is 75 mg twice daily for 5 days 4
• The recommended dose of zanamivir for treatment of influenza in adults and pediatric patients aged 7 years and older is 10 mg twice daily for 5 days 6

Prevention of Influenza URTI

• Influenza vaccination is the primary preventive measure against influenza-related URTI 1
• Recommendations for influenza vaccination vary worldwide:
  • In the United States: recommended for children ≥6 months of age
  • In the United Kingdom: recommended for children from 2 years of age
  • In the Netherlands: restricted to children with substantial medical comorbidities 1
• Both inactivated influenza vaccines and live attenuated influenza vaccines have been shown to reduce influenza infection and associated complications 1

Distinguishing Features from Other URTIs

• Influenza URTI typically presents with more abrupt onset and more severe systemic symptoms compared to common cold caused by other viruses 1
• Fever is more common and typically higher in influenza compared to other viral URTIs 1
• The absence of fever makes influenza less likely as a cause of URTI 1
• Paroxysmal cough is highly sensitive (93.2%) but not specific for pertussis, and can help differentiate it from influenza URTI 1

Clinical Pearls and Pitfalls

• Not all influenza infections progress to lower respiratory tract involvement; many remain limited to the upper respiratory tract 1, 5
• Bacterial superinfections can complicate influenza URTI, so worsening symptoms after initial improvement should raise suspicion for secondary bacterial infection 6
• Antiviral medications are most effective when started within 48 hours of symptom onset 4, 6
• Influenza can co-circulate with other respiratory viruses, and co-infections are possible 2, 7
• Early intervention in URTI is crucial to reduce symptom severity and viral transmission 8