Influenza

Introduction

In 2007, influenza caused 411 deaths: 79 of them in persons aged 75-84 years and 139 of them in persons aged 85 years and older (Xu et al, 2007)

Hosts

Human and animal

Transmission / Exposure Route

Transmission of influenza from poultry or pigs to humans occurs by direct contact with infected animals. The risk is especially high during slaughter and preparation for consumption; eating properly cooked meat poses no risk. Avian influenza can also be spread through exposure to water and surfaces contaminated by bird droppings. Influenza viruses spread from human to human via aerosols created by coughs or sneezes of infected individuals. Influenza virus infection occurs after inhalation of the aerosol by a person who is immunologically susceptible. ^[1]

Case Fatality Ratio

In the United States in 2006, influenza caused 849 deaths, 608 of them in persons aged 75 years and older.^[2] 
In 2007, influenza caused 411 deaths: 79 of them in persons aged 75-84 years and 139 of them in persons aged 85 years and older ^[3]

Incubation Period

18-72 hours^[1]

Burden of Disease

Each year approximately 500,000 deaths worldwide are attributed to Influenza virus infection. ^[4] Influenza can cause seasonal, endemic, and sometimes pandemic infections. The worst pandemic, in 1918, killed approximately 50 million people worldwide. ^[5]

Duration of infectiousness and disease

Infected individuals often see symptoms for 7-10 days. ^[5] Influenza virus is contagious and is transmittable 1 day before symptoms appear and up to 7 days after becoming ill. ^[2]

Symptomology

Symptoms include fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue, vomiting and diarrhea (common in children). Pneumonia can develop as a result of Influenza virus infection. ^[2]

Latency

Asymptomatic Rates

Excretion Rates (see Exposure)

Immunity

Seasonal Influenza vaccines are sufficient to protect from the most common forms of Influenza virus. ^[2]

Microbiology

Encapsulated, negative-sense, single-stranded RNA viruses of the family Orthomyxoviridae^[1]