Impact of influenza during the post-pandemic season: epidemiological picture from syndromic and virological surveillance.

INTRODUCTION

Following the observation that 1 or 2 pandemic peak due to the circulation ofAHINlv had occurred in most countries and in most World Health Organization (WHO) Regions, WHO declared on August 10"h, 2010 that the world was moving into the post-pandemic period, whose surveillance presents considerable interest both from epidemiological and clinical point of view. We described the epidemiological picture emerged from syndromic and virological surveillance during the post-pandemic season in Liguria, Italy.

MATERIALS AND METHODS

An Emergency Department Syndrome surveillance system, based on data collected at "San Martino" and IRCCS "G. Gaslini" Liguria Regional Reference University Hospitals for adults and children is active since July 2007. Monitored syndromes include "Influenza-Like Illness" (ILl) and "Low Respiratory Tract Infections" (LRTI). The Ligurian Regional Reference laboratory for Influenza virological surveillance and diagnosis offers rapid detection of influenza viruses by real-time and block RT-PCR, viral culture and genetic characterization by entire sequence analysis of haemagglutinin- and neuraminidase-coding regions in accordance with the international standards established by the global laboratory network.

RESULTS AND DISCUSSION

The integration of syndromic surveillance system and laboratory surveillance for rapid detection and characterization of the disease responsible agent represented a specific and sensitive tool for influenza surveillance. The post-pandemic season was characterized by early onset and by the heaviest impacts for ILI and LRTI among the recent epidemic seasons. In contrast to the picture observed during the pandemic season, the 2010/11 winter was characterized by the intensive circulation of pandemic AH1N1v coupled with sustained activity due to influenza B and Respiratory Syncytial Virus (RSV). Antigenic and molecular characterization of influenza strains confirmed the good matching between circulating and 2010/11 vaccine viruses.