Vaccination contre l’hépatite A : autour du cas index

[Study of a population outbreak of hepatitis A. Effectiveness of vaccination as a control measure]

OBJECTIVE

To describe an outbreak of hepatitis A in the city of Albacete (Spain) and to assess the effectiveness of the control measures implemented.

METHODS

When the outbreak was noted, definitions of a case were established. Clinical and epidemiological data were collected through a survey. The temporal-spatial distribution was identified through mapping and the epidemic curve. Health education and immunoglobulin (IG) administration were conducted as immediate prevention and control measures in the population at risk.

RESULTS

From January 2005 to January 2006, 62 cases were reported. The most affected age groups were school children and young adults. Transmission was person to person. The epidemic curve was divided into two periods. Initial control measures consisted of hygiene measures and IG administration to contacts. In the second period, these measures were complemented with vaccination against hepatitis A in students of the school centers of the two neighborhoods initially involved. Due to public alarm and spread of the outbreak to adjacent neighborhoods, vaccination was extended to schools close to those where cases had been detected. No cases were notified after the last vaccination in January 2006.

CONCLUSIONS

The use of vaccination after exposure to the hepatitis A virus in young adults and the school population seems to be an effective outbreak control measure.

[Laboratory based hepatitis A surveillance in New Caledonia: from an endemic to an epidemic pattern (1986-2007)]

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.

Bayesian coalescent inference of hepatitis A virus populations: evolutionary rates and patterns

Hepatitis A virus (HAV) is a hepatotropic member of the family Picornaviridae. Previous studies suggested that HAV may evolve more slowly than other members of the family. To estimate HAV substitution rates precisely, we used a Bayesian Markov chain Monte Carlo (MCMC) approach on temporally sampled HAV VP1 full-length sequences from strains isolated in France. A mean rate of evolutionary change of 9.76×10−4 nucleotide substitution per site per year was found. The results also revealed that the synonymous rate found for HAV is lower than that of other members of the family. Bayesian skyline plots revealed a sharp decline in the effective number of infections in 1996, coinciding with the introduction of HAV vaccine.