Diagnosing and Treating Influenza in the Emergency Department: An Evidence-Based Update

Why can influenza severity be difficult to assess?

Influenza has a wide spectrum of illness, and its presentation can be atypical in vulnerable patients. The issue reviews clinical features associated with severe disease and complications.

When is influenza testing most useful in the ED?

Testing has the greatest value when it informs care decisions. The review addresses diagnostic stewardship alongside treatment, infection control, and disposition considerations.

How do rapid antigen and molecular tests differ?

The available tests differ in accuracy, turnaround time, cost, and local availability. The issue examines these tradeoffs and common interpretation challenges.

How does patient risk affect antiviral decisions?

Expected benefit and treatment considerations vary with illness severity, patient risk, and symptom duration. The review covers antiviral selection across adult, pediatric, pregnant, and immunocompromised populations.

What complicates the course of influenza?

Bacterial superinfection, respiratory failure, and extrapulmonary complications can contribute to deterioration. The issue also explores coinfection with SARS-CoV-2 and the challenges of distinguishing overlapping illnesses.

CASE 1 — Influenza in an Older Long-Term Care Resident: An 81-year-old man with heart failure and Alzheimer disease presents with fever, cough, confusion, poor intake, and hypoxemia during an outbreak at his facility; testing detects influenza A. The case highlights assessment of complications and treatment considerations in a vulnerable patient several days into illness.

CASE 2 — Mild Illness and a Request for Antivirals: A healthy 28-year-old schoolteacher presents early in a febrile respiratory illness and requests treatment to help her return to work. The case explores whether testing will change care and how expected benefit, adverse effects, and patient preferences shape treatment discussions.

CASE 3 — Influenza and a Seizure in a Young Child: A 2-year-old boy returns to his baseline mental status after a brief generalized seizure during a febrile respiratory illness, and testing detects influenza B. The case frames the challenges of weighing age-related risk, antiviral treatment, and the appropriate level of ongoing care.

• An overview of the estimated annual US influenza burden and an illustration of influenza virus structure and subtyping.
• A differential diagnosis summary for influenza-like illness and a comparison of common clinical features in adults and children.
• A reference covering clinical features associated with severe or complicated influenza.
• A summary of patient populations at high risk for influenza complications.
• A comparison of influenza testing methods, including accuracy and time to results.
• Antiviral medication references for adults and children, including adult renal impairment considerations.
• A summary of ED disposition considerations across influenza presentations.
• A clinical pathway for ED management of suspected influenza, integrating patient risk, testing, treatment, and disposition.

• Excluding influenza after a negative rapid antigen test.
• Overlooking atypical presentations without fever.
• Applying the symptom-duration cutoff rigidly to high-risk patients.
• Dismissing deterioration after initial improvement.
• Choosing an antiviral without considering pregnancy-specific limitations.