Norovirus in the Maltese community

Abstract

Key words: Norovirus, community, sentinel surveillance, sample collection, viral strain identification, GII/4 2006b Noroviruses are the most frequent cause of acute gastroenteritis in the community, often responsible for major outbreaks in institutions or crowded areas such as schools, hospitals, hotels, cruise ships and facilities for the elderly. Although symptoms are usually mild and short lasting, norovirus infection can occasionally be severe, prolonged and even fatal in certain subgroups including children, the elderly and the immunocompromised. The high infectivity, environmental stability, strain diversity and multiple modes of transmission of norovirus contribute to the high burden of this infection in the community. Recently, the new GII.4-2006b variant has been described as being responsible for an increase of norovirus outbreaks across Europe. Owing to under reporting of infectious intestinal diseases and lack of local diagnostic tests, the true burden and identity of circulating noroviral strains in Malta is unknown. A sentinel surveillance system was set up between November 2008 and February 2009. Patients presenting with acute gastroenteritis to 15 volunteering general practitioners, and who fitted the case definition, were asked to participate in the study. Consenting patients were then followed. up and the stool or vomitus samples collected were tested for the presence of the virus followed by strain identification. A total of 115 patients were recruited in the study, 66.1 % of whom submitted a sample for testing. 51 % of the samples collected tested positive for norovirus. The presence of vomiting was significantly associated with patients positive for norovirus. In addition, the number of daily episodes of vomiting was positively associated with an increased risk for household outbreaks. 64% of those positively identified reported person to person transmission of infection. Following laboratory investigation, the GII.4-2006b strain was identified in all but one of the sequenced samples. This circulating strain is identical to the current described circulating strain in many European countries. The study indicates that norovirus infection is frequent in the community and thus represents a potentially important public health problem. This emphasizes the need for an extensive and prolonged surveillance of norovirus gastroenteritis in order to evaluate the true burden of the viral illness in the community and identify peaks of activity. Consequently, the health authorities would be able inform the public and institutional facilities about the increased risk of norovirus outbreaks and in the process raise public awareness about measures to prevent norovirus infection.