An Epidemiological Analysis of Summer Influenza Epidemics in Okinawa

Abstract

Objective This study evaluates the difference between winter influenza and summer influenza in Okinawa. Methods From January 2007 to June 2014, weekly rapid antigen test (RAT) results performed in four acute care hospitals were collected for the surveillance of regional influenza prevalence in the Naha region of the Okinawa Islands. Results An antigenic data analysis revealed that multiple H1N1 and H3N2 viruses consistently co-circulate in Okinawa, creating synchronized seasonal patterns and a high genetic diversity of influenza A. Additionally, influenza B viruses play a significant role in summer epidemics, almost every year. To further understand influenza epidemics during the summer in Okinawa, we evaluated the full genome sequences of some representative human influenza A and influenza B viruses isolated in Okinawa. Phylogenetic data analysis also revealed that multiple H1N1 and H3N2 viruses consistently co-circulate in Okinawa. Conclusion This surveillance revealed a distinct epidemic pattern of seasonal and pandemic influenza in this subtropical region.

Inter‐seasonality of influenza in Australia

“…For example, tropical and subtropical countries such as Thailand and Hong Kong have two seasonal peaks of influenza per year . In temperate regions, outbreaks of influenza A and B are also reported during summer . Australia typically has a single winter peak, and summer influenza outbreaks are uncommon.…”

“…24 In temperate regions, outbreaks of influenza A and B are also reported during summer. 13,[25][26][27] Australia typically has a single winter peak, and summer influenza outbreaks are uncommon. Globally, there are reports of summer influenza or out-of-season outbreaks in institutions, as well as among travellers on cruise ships.…”

“…They showed the onset of epidemics varies season to season; however, there is remarkable synchronisation of epidemic onset across Australia, with a winter peak typically in August, despite the significant distance involved and variation in climate . There have also been reported increased cases of summer influenza or out‐of‐season epidemic in other countries . We aimed to determine whether inter‐seasonal influenza activity has been increasing in Australia over time.…”

“…12 There have also been reported increased cases of summer influenza or out-of-season epidemic in other countries. 13 We aimed to determine whether inter-seasonal influenza activity has been increasing in Australia over time.…”

The selection pressure on the neuraminidase gene of influenza viruses isolated in Ukraine from 2009 to 2015

“…The analysis of the nucleotide sequences of HA and NA genes of the viruses isolated from patients in different parts of the globe is widely used to predict the evolutionary variability of the influenza virus as well as to predict the emergence of new epidemic strains using mir-journal.org Selection pressure on the NA gene bioinformatics methods, in particular by phylogenetic analysis [8]. In recent years, phylogenetic analysis has become one of the main components of epidemiological surveillance, which is used to determine the relationship and evolution of influenza viruses [9]. Despite the fact that many research projects devoted to the study of the selection pressure on the genes of human influenza viruses have already been performed, the relationship between positively selected sites, antigenic variability of the virus, and sensitivity to NA inhibitors are still not fully understood [10][11][12].…”