- Published on
Emergency And Acute Medicine – Influenza
Basics
Description Influenza is an acute, usually self-limited viral respiratory infection transmitted via small-particle aerosols from coughing, sneezing, or talking. The virus infects respiratory epithelium after deposition in the airway. Incubation is 1–4 days (average 2), with a mean illness duration of approximately 4 days in adults. Seasonal outbreaks peak most commonly in winter, often February. Mortality is largely due to pulmonary complications. Complications include primary viral pneumonia, secondary bacterial pneumonia, COPD exacerbations, otitis media and sinusitis in children, reactive airway disease, and rarely myositis, myocarditis, pericarditis, Guillain–Barré syndrome, aseptic meningitis, ARDS, and multisystem organ failure.
Etiology
Influenza is caused primarily by influenza A or B viruses, with influenza A generally producing more severe disease. Influenza A is classified by hemagglutinin (H1, H2, H3) and neuraminidase subtypes. Annual epidemics result from antigenic drift, while pandemics result from antigenic shift. Waterfowl serve as the primary reservoir. Vaccine targets circulating subtype antigens.
Diagnosis
Signs and symptoms Influenza-like illness is defined as fever with cough or sore throat without another clear diagnosis. Fever and cough together are somewhat specific but insensitive. Children often have higher fevers, more lower respiratory involvement, calf myalgias, and febrile seizures. Elderly patients may present atypically with confusion, lassitude, or minimal respiratory symptoms. Local epidemic activity is the strongest predictor of disease.
Essential workup
Diagnosis is primarily clinical during influenza season when community prevalence is high.
Diagnosis tests and interpretation
Lab CBC may show normal or mildly decreased WBC count. Pulse oximetry or ABG is indicated for significant respiratory symptoms.
Imaging Chest radiograph is indicated for lower respiratory findings and may be normal or show bilateral interstitial infiltrates.
Diagnostic procedures Rapid antigen tests are specific but poorly sensitive. PCR testing is both sensitive and specific and can differentiate subtypes. Viral culture is not useful for ED decision-making.
Differential diagnosis
Other respiratory viral infections, bronchitis, atypical pneumonia, infectious mononucleosis, and rarely anthrax.
Treatment
Initial stabilization Provide supplemental oxygen, IV fluids, and ventilatory support as indicated.
Emergency department management Treatment is primarily supportive with antipyretics, hydration, and bronchodilators for bronchospasm. Avoid aspirin, especially in children. Neuraminidase inhibitors (oseltamivir, zanamivir) are most effective when started within 48 hours of symptom onset and reduce symptom duration by less than one day. Antivirals are recommended for severe illness, hospitalized patients, immunocompromised individuals, and those at high risk for complications.
Medication
Oseltamivir 75 mg PO BID for treatment or 75 mg PO daily for postexposure prophylaxis. Zanamivir inhalation 10 mg q12h. Albuterol for associated bronchospasm.
Prevention
Annual inactivated influenza vaccination is recommended for high-risk groups, health care workers, pregnant women, and children. Live attenuated intranasal vaccine is approved for healthy individuals aged 2–49 years but contraindicated in pregnancy, immunocompromise, and certain comorbidities. Chemoprophylaxis may be used in selected high-risk exposures.
Follow-up and disposition
Admission criteria Hypoxia, pneumonia, severe dehydration, altered mental status, or inability to tolerate oral intake.
Discharge criteria Stable patients tolerating fluids with mild disease.
Follow-up recommendations Outpatient follow-up and return precautions for worsening respiratory symptoms.
Pearls and pitfalls
Local influenza prevalence is the most important diagnostic clue. Most patients do not require testing or antivirals. Consider concurrent reactive airway disease in patients with wheezing or hypoxia. Stay updated with seasonal CDC guidance.
Basics
Description Influenza is an acute, usually self-limited viral respiratory infection transmitted via small-particle aerosols from coughing, sneezing, or talking. The virus infects respiratory epithelium after deposition in the airway. Incubation is 1–4 days (average 2), with a mean illness duration of approximately 4 days in adults. Seasonal outbreaks peak most commonly in winter, often February. Mortality is largely due to pulmonary complications. Complications include primary viral pneumonia, secondary bacterial pneumonia, COPD exacerbations, otitis media and sinusitis in children, reactive airway disease, and rarely myositis, myocarditis, pericarditis, Guillain–Barré syndrome, aseptic meningitis, ARDS, and multisystem organ failure.
Etiology
Influenza is caused primarily by influenza A or B viruses, with influenza A generally producing more severe disease. Influenza A is classified by hemagglutinin (H1, H2, H3) and neuraminidase subtypes. Annual epidemics result from antigenic drift, while pandemics result from antigenic shift. Waterfowl serve as the primary reservoir. Vaccine targets circulating subtype antigens.
Diagnosis
Signs and symptoms Influenza-like illness is defined as fever with cough or sore throat without another clear diagnosis. Fever and cough together are somewhat specific but insensitive. Children often have higher fevers, more lower respiratory involvement, calf myalgias, and febrile seizures. Elderly patients may present atypically with confusion, lassitude, or minimal respiratory symptoms. Local epidemic activity is the strongest predictor of disease.
Essential workup
Diagnosis is primarily clinical during influenza season when community prevalence is high.
Diagnosis tests and interpretation
Lab CBC may show normal or mildly decreased WBC count. Pulse oximetry or ABG is indicated for significant respiratory symptoms.
Imaging Chest radiograph is indicated for lower respiratory findings and may be normal or show bilateral interstitial infiltrates.
Diagnostic procedures Rapid antigen tests are specific but poorly sensitive. PCR testing is both sensitive and specific and can differentiate subtypes. Viral culture is not useful for ED decision-making.
Differential diagnosis
Other respiratory viral infections, bronchitis, atypical pneumonia, infectious mononucleosis, and rarely anthrax.
Treatment
Initial stabilization Provide supplemental oxygen, IV fluids, and ventilatory support as indicated.
Emergency department management Treatment is primarily supportive with antipyretics, hydration, and bronchodilators for bronchospasm. Avoid aspirin, especially in children. Neuraminidase inhibitors (oseltamivir, zanamivir) are most effective when started within 48 hours of symptom onset and reduce symptom duration by less than one day. Antivirals are recommended for severe illness, hospitalized patients, immunocompromised individuals, and those at high risk for complications.
Medication
Oseltamivir 75 mg PO BID for treatment or 75 mg PO daily for postexposure prophylaxis. Zanamivir inhalation 10 mg q12h. Albuterol for associated bronchospasm.
Prevention
Annual inactivated influenza vaccination is recommended for high-risk groups, health care workers, pregnant women, and children. Live attenuated intranasal vaccine is approved for healthy individuals aged 2–49 years but contraindicated in pregnancy, immunocompromise, and certain comorbidities. Chemoprophylaxis may be used in selected high-risk exposures.
Follow-up and disposition
Admission criteria Hypoxia, pneumonia, severe dehydration, altered mental status, or inability to tolerate oral intake.
Discharge criteria Stable patients tolerating fluids with mild disease.
Follow-up recommendations Outpatient follow-up and return precautions for worsening respiratory symptoms.
Pearls and pitfalls
Local influenza prevalence is the most important diagnostic clue. Most patients do not require testing or antivirals. Consider concurrent reactive airway disease in patients with wheezing or hypoxia. Stay updated with seasonal CDC guidance.
0 Comments
