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

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. OBJECTIVE: Describe the data generated by the influenza A(H1N1) pdm09 surveillance in Saudi Arabia from 2010 to 2016. DESIGN: Retrospective, descriptive. SETTING: Hospitals reporting to the Ministry of Health. MATERIALS AND METHODS: We studied aggregate data on hospitalized cases of influenza A(H1N1)pdm09 in Saudi Arabia between 2010 and 2016. The surveillance system used the case definition proposed by the WHO. The cases were confirmed by performing the real-time PCR (polymerase chain reaction) on upper respiratory samples. MAIN OUTCOME MEASURES: Suspected and confirmed influenza A(H1N1)pdm09 cases. SAMPLE SIZE: 113 502 suspected H1N1 cases and 17 094 (15.1%) confirmed cases. RESULTS: Most of the reported cases were registered in the Riyadh region. During the period of the study, the highest number of confirmed cases, 9262 (54.2 %), was in 2015. The case fatality rate for confirmed cases was 3.6%. CONCLUSION: Influenza A(H1N1)pdm09 showed seasonal trends. The number of suspected influenza cases each year was proportionate to the number of confirmed cases for that year. Riyadh, Jeddah and the Eastern areas (regions with the highest population) reported most of the cases. LIMITATION: Only one strain of H1N1 was tested. CONFLICT OF INTEREST: None.