Influenza: Epidemiology, Clinical Features, Therapy, and Prevention

Abstract

Influenza A and B are important causes of respiratory illness in all age groups. Influenza causes seasonal outbreaks globally and, less commonly, pandemics. In the United States, seasonal influenza epidemics account for >200,000 hospitalizations and >30,000 deaths annually. More than 90% of deaths occur in the elderly population. Interestingly, in the novel 2009 H1N1 influenza pandemic, attack rates were highest among children and young adults. Fewer than 10% of cases occurred in adults >60 years old, likely because preexisting antibodies against other H1N1 viruses afforded protection. Despite concerns about a high lethality rate with the novel 2009 H1N1 strain, most illnesses caused by the 2009 H1N1 viruses were mild (overall case fatality rate <0.5%). Clinical features of influenza infection overlap with other respiratory pathogens (particularly viruses). The diagnosis is often delayed due to low suspicion and the limited use of specific diagnostic tests. Rapid diagnostic tests are widely available and allow detection of influenza antigen in respiratory secretions within 1 hour; however, sensitivity ranges from 50 to 90%. Neuraminidase inhibitors (NAIs) (eg, oseltamivir and zanamivir) are effective for treating influenza A or B and for prophylaxis in selected adults and children. Resistance to NAIs is rare, but influenza strains resistant to oseltamivir have been detected. Vaccines are the cornerstone of influenza control. Currently, trivalent inactivated vaccine (TIV) and live attenuated influenza vaccine (LAIV) are available. These agents reduce mortality and morbidity in high-risk patients (i.e., the elderly or patients with comorbidities), and expanding the use of vaccines to healthy children and adults reduces the incidence of influenza, pneumonia, and hospitalizations due to respiratory illnesses in the community.

Impact of vitamin D administration on immunogenicity of trivalent inactivated influenza vaccine in previously unvaccinated children

“…14 Patients with chronic and severe underlying diseases are at the highest risk of influenza-related complications, but otherwise healthy subjects can also develop severe influenza, particularly if they are less than five years of age. 15,16 The potential severity of the disease and the role played by children in spreading the infection explain why influenza vaccination is strongly recommended throughout the world for children with chronic and severe underlying diseases and, in an increasing number of countries, for at least the youngest healthy subjects. 17,18 Unfortunately, the protection induced by TIV in younger children is not optimal because of the immaturity of the immune system in the first years of life.…”

The significance of naturally occurring neuraminidase quasispecies of H5N1 avian influenza virus on resistance to oseltamivir: a point of concern

“…HPAI virus of the subtype H5N1, discovered for the first time in 1996 in Guangdong province in China, was the precursor of the H5N1 virus that spread to humans in Hong Kong (Xu et al, 1999) and has since caused numerous outbreaks in poultry in South-east Asia and continues to be endemic in many parts of the world such as Asia, Africa and the Middle East (Clark & Lynch, 2011;Neumann et al, 2010). Avian influenza continues to present a significant risk to human health due to persistent outbreaks, making it a potential candidate for causing an influenza pandemic.…”

Postinfection A77-1726 Treatment Improves Cardiopulmonary Function in H1N1 Influenza-Infected Mice

“…Influenza A viruses cause a highly contagious acute respiratory illness in humans (1). Currently, seasonal influenza accounts for 200,000 hospitalizations and more than 36,000 excess deaths per year in the United States alone, and is the eighth leading cause of annual mortality in this country (2).…”