Clinical Background
Influenza is an acute viral infection that occurs in outbreaks of varying severity throughout the winter.
Epidemiology
- Incidence - >1/1,000
- Age
- Attack rates highest in young children
- Mortality highest in elderly
- Transmission - respiratory droplet, airborne route
Organism
- Single-stranded RNA virus
- Family - Orthomyxovindae
- Three types based on antigenic differences - A, B, C
- Only A undergoes antigenic shift
- Antigenic shift is responsible for pandemics
- Classified by hemagglutinin (HA)/neuramidase (NA) activity
- Named with H and N components: H1-15 and N1-9
Risk Factors
- Chronic pulmonary disease - especially asthma
- Chronic renal, cardiovascular or metabolic diseases
- Elderly
- Immunocompromised state
- Pregnancy
Clinical Presentation
- Abrupt onset of fever, chills, myalgias and malaise
- Severe retroorbital headache, sore throat
- Cough and upper respiratory infection signs and symptoms occur 3-4 days after initial onset
- Complications
- Primary viral influenzal pneumonia
- Secondary bacterial pneumonia
- Myositis
- Myocarditis, pericarditis
- Guillain Barré, transverse myelitis, encephalitis
- Reye syndrome
Treatment
- Current antivirals given within 48 hours of symptoms may lessen the severity of the course
- Neuraminidase inhibitors are used for treatment and prophylaxis against Influenza A and B
- Most strains of Influenza A are considered resistant to treatment with amantadine sulfate (>95%)
- Supportive
Prevention
- Yearly vaccination
- Inactivated - intramuscular
- Live attenuated - intranasal
- Contraindicated in settings of immunocompromised persons or households with persons who are immunocompromised
- Antiretroviral prophylaxis with neuraminidase inhibitors when vaccination is contraindicated
Refer to Influenza topic at www.arupconsult.com for CDC Seasonal Influenza Vaccination Resources for Health professional
