Chapter 41: Influenza

INTRODUCTION

• Influenza is a viral illness associated with high mortality and high hospitalization rates. The highest rates of severe illness, hospitalization, and death occur among those older than age 65 years, young children (younger than 2 years old), and those who have underlying medical conditions, including pregnancy and cardiopulmonary disorders.

• The route of influenza transmission is person-to-person via inhalation of respiratory droplets, which can occur when an infected person coughs or sneezes. The incubation period for influenza ranges between 1 and 7 days, with an average incubation of 2 days. Adults are considered infectious from the day before their symptoms begin through 7 days after the onset of illness, whereas children can be infectious for longer than 10 days after the onset of illness. Viral shedding can persist for weeks to months in severely immunocompromised people.

CLINICAL PRESENTATION

• The presentation of influenza is similar to a number of other respiratory illnesses.

• The clinical course and outcome are affected by age, immunocompetence, viral characteristics, smoking, comorbidities, pregnancy, and the degree of preexisting immunity.

• Complications of influenza may include exacerbation of underlying comorbidities, primary viral pneumonia, secondary bacterial pneumonia or other respiratory illnesses (eg, sinusitis, bronchitis, and otitis), encephalopathy, transverse myelitis, myositis, myocarditis, pericarditis, and Reye syndrome.

SIGNS AND SYMPTOMS

• Classic signs and symptoms of influenza include rapid onset of fever, myalgia, headache, malaise, nonproductive cough, sore throat, and rhinitis.

• Nausea, vomiting, and otitis media are also commonly reported in children.

• Signs and symptoms typically resolve in 3 to 7 days, although cough and malaise may persist for more than 2 weeks.

LABORATORY TESTS

• The gold standard for diagnosis of influenza are reverse-transcription polymerase chain reaction (RT-PCR) or viral culture.

• Rapid influenza diagnostic tests [(RIDTs), also known as point-of-care (POC) tests], direct (DFA) or indirect (IFA) fluorescence antibody tests, and the RT-PCR assay may be used for rapid detection of virus.

• Chest radiograph should be obtained if pneumonia is suspected.

PREVENTION

• The best means to decrease the morbidity and mortality associated with influenza is to prevent infection through vaccination. Appropriate infection control measures, such as hand hygiene, basic respiratory etiquette (cover your cough and throw tissues away), and contact avoidance, are also important in preventing the spread of influenza.

• Annual vaccination is recommended for all persons age 6 months or older and caregivers (eg, parents, teachers, babysitters, nannies) of children less than 6 months of age.

• Vaccination is also recommended for those who live with and/or care for people who are at high risk, including household contacts and healthcare workers.

• The Advisory Committee on Immunization Practices (ACIP) has made the following recommendations regarding the vaccinations of persons with reports of egg allergy: (a) Vaccination with any age appropriate IIV or RIV3 vaccine, for persons with a history of egg allergy that involves ...