Influenza surveillance by age and target group

Reconstruction of epidemic curves for pandemic influenza A (H1N1) 2009 at city and sub-city levels

To better describe the epidemiology of influenza at local level, the time course of pandemic influenza A (H1N1) 2009 in the city of Hong Kong was reconstructed from notification data after decomposition procedure and time series analysis. GIS (geographic information system) methodology was incorporated for assessing spatial variation. Between May and September 2009, a total of 24415 cases were successfully geocoded, out of 25473 (95.8%) reports in the original dataset. The reconstructed epidemic curve was characterized by a small initial peak, a nadir followed by rapid rise to the ultimate plateau. The full course of the epidemic had lasted for about 6 months. Despite the small geographic area of only 1000 Km2, distinctive spatial variation was observed in the configuration of the curves across 6 geographic regions. With the relatively uniform physical and climatic environment within Hong Kong, the temporo-spatial variability of influenza spread could only be explained by the heterogeneous population structure and mobility patterns. Our study illustrated how an epidemic curve could be reconstructed using regularly collected surveillance data, which would be useful in informing intervention at local levels.

Characterizing the initial diffusion pattern of pandemic (H1N1) 2009 using surveillance data

Using notification data, diffusion of pandemic human influenza A (H1N1) 2009 in Hong Kong was explored with geographic information system (GIS) methodology. Point data were displayed and then analysed with interpolation and the application of SaTScan™. Beginning from 6 initial foci, the spatial distribution has remained heterogeneous at the end of the first three months, with students functioning as the main disseminators. Our study showed that routinely collected surveillance data could be effectively used for describing the epidemic, which could support the development of interventions at local levels.

[Serological investigation of influenza type A and B in university students, Brazil]

Wide serological prevalence of influenza A and B was verified by the serological survey covering 200 students of the University of S. Paulo during the 1984-1985 period. The humoral antibodies were detected by the single radial haemolysis technique, whose arithmetic titres averages were greater for both subtypes, (H1N1) and (H3N2) of the influenza A virus strains recently isolated from the population. However, the situation of this type B virus was not the same as that of type A seeing that the B/Engl/847/73, although an older strain, showed better reactogenicity than the other strains evaluated. It is possible that is was responsible for the primo infection of most of the components of the group surveyed, as the phenomenon of the "Original Antigenic Sin" explains. The antibody responses to subtypes of influenza A and B in this survey demonstrated levels with low SRH titres (2.5 to 3.5 mm) and high SRH titres (> or = 4.0 mm) related to the lowest and highest levels of suggest protection against infection. Individual immunity and persistence of antibody are related to frequency and recent occurrence of exposition to influenza. As concerns the formulation of influenza vaccine it was established that this preserves the antigen selection of the new strains isolated from the population, mainly due to the behavior of the influenza A virus.