Hospital-based surveillance of influenza A(H1N1)pdm09 virus in Saudi Arabia, 2010-2016

Abdalla, Osman; Mohammed, Mutaz; Hakawi, Ahmed Mohammed; Aljifri, Alanoud; Abdalla, Mohamed; Eltigani, Sara; Mujib, Sahibzada Azhar; Assiri, Abdullah

BACKGROUND: Influenza is a highly contagious acute viral respiratory tract infection. The emergence of influenza A(H1N1)pdm09 in 2009 caused a pandemic. Since then it has become a seasonal influenza virus. It causes symptoms ranging from mild to severe illness, which might be fatal, particularly in people with underlying chronic medical conditions,immunocompromised people, the elderly, and pregnant women. I nfluenza is an acute, highly contagious viral infection of the respiratory tract that infects both humans and animals. [1] [2] [3] [4] Human influenza viruses are single-stranded RNA viruses that belong to the Orthomyxoviridae family, consisting of the genera influenza A, B, and C viruses. A new strain of influenza A(H1N1) virus known as influenza A(H1N1)pdm09 emerged in 2009 causing a global influenza pandemic (official nomenclature from Pandemic Disease Mexico 2009). [5] [6] [7] This strain now cocirculates with other seasonal viruses. 7 Only influenza A and B viruses cause epidemics in humans. [8] [9] [10] Influenza viruses circulate, causing disease in humans every year. In temperate climates, the disease tends to occur seasonally in the winter months. 11 Influenza viruses can be transmitted through aerosols, large droplets, or direct contact with secretions (or fomites). Seasonal influenza viruses can cause a wide range of symptoms from mild to severe illness, which can lead to death, particularly in persons at increased risk for severe disease, including pregnant women, the very young and very old, immunocompromised people, and people with chronic underlying medical conditions. 12 Seasonal influenza viruses evolve continuously, which means that people can be infected multiple times throughout their lives. 13 Therefore, the components of seasonal influenza vaccines are reviewed frequently (currently biannually) and updated periodically to ensure the continued effectiveness of the vaccines. 14 A pandemic occurs when an influenza virus, which is not previously known to be circulating among humans and to which most people do not have immunity, emerges and transmits among humans. These viruses may emerge, circulate, and cause large outbreaks outside of the normal influenza season. 15, 16 The World Health Organization (WHO) was called in 2005 to strengthen the surveillance system of all events of international public health concern. 17 The strengthening of the influenza surveillance system was set as a goal by WHO and concerned bodies in 2009, following the emergence of the novel strain of influenza virus A(H1N1)pdm09.