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

Calculating the case fatality rate (CFR) is dependent on estimates of the denominator. Using the denominator of symptomatic (suspected cases) of 113 588, suggests an overall CFR of 0.54% (95%CI: 0.50-0.58) and Table 1 . The seasonal trend in the data is consistent with the Northern Hemisphere influenza season. 11, 12 The year 2015 had the highest number of cases, suspected cases, confirmed cases, and deaths. This finding is likely due to the outbreak of influenza during and after Hajj 2015, especially in the areas of Makkah and Jeddah, and a policy of testing all suspected cases of MERS CoV to Influenza A(H1N1)pdm09 issued in the second half of the year 2014. The most densely populated regions: Riyadh, Jeddah, Makkah and Eastern, comprises 70% of the Saudi population. These four regions reported 62.4% of A(H1N1)pdm09 cases. The Riyadh region reported the highest number of cases (3818, 22.3%), followed by Jeddah (3378, 19.8%). The population density and crowdedness in these two regions may have predisposed to some A(H1N1)pdm09 outbreaks during winter seasons of 2015. There may be under-reporting from other regions, leading to an underestimation of the true disease burden. Aljouf and Hafr Albatin reported the least cases in seven years (38 and 35 cases, consecutively).