This study aimed at describing the evolution of the epidemiological pattern of hepatitis A in New Caledonia since 1986 and the recent epidemic which occurred in 2005-2006, regarding particularly its demographic and virological aspects and the public health response implemented. The annual or monthly activity records for Hepatitis A sero-diagnostic performed at the Pasteur Institute of New Caledonia were processed in a retrospective analysis (9723 samples tested for the detection of IgM to hepatitis A). Over the 2004-2006 period, a phylogenetic study of representative strains from New Caledonia and other Pacific islands was carried out by the French National Reference Laboratory for hepatitis A (Paul-Brousse hospital, Villejuif, France).
Results: The continuous improvement of hygiene that occurred in New Caledonia during the last two decades led to a dramatic drop in the frequency of hepatitis A among patients tested, ranging from an average value of 79 cases (14%) for the 1986-1999 period to 0 case from 2002. However, in 2005, a strong increasing number of confirmed cases was notified, mainly among young people (78% were under the age of 20). In 2006, this epidemic reached the island of Futuna where it involved more than 1% of the total population (56 cases). The phylogenetic study has confirmed the clonality of the virus circulating during this epidemic, not related to other regional strains (Fiji, Vanuatu, New Zealand) nor with a New Caledonian strain from the previous endemic period. This transition situation, with persistence of a high epidemic risk, should encourage the health authorities to implement adapted response strategies, based in particular on systematic case declaration and targeted immunisation programmes.