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Interferon-gamma assays in TB diagnosis
P16 TB Infection in the UK indigenous white elderly population: a retrospective study of interferon gamma release assays (IGRAs)
  1. M Gautam1,
  2. J Darroch2,
  3. P Davies3
  1. 1Aintree University Hospital, Liverpool, UK
  2. 2Royal Liverpool University Hospital, Liverpool, UK
  3. 3Liverpool Heart and Chest Hospital, Liverpool, UK

Abstract

Introduction Recent data from The Health Protection Agency (HPA) UK indicates a further rise in the incidence of TB and about 15% cases of newly diagnosed cases of TB occur in those aged =65. Within the indigenous white population in the UK, it is the elderly population in whom TB is principally an issue. In contrast to previous studies looking at TST positivity, the application of IGRAs to detect infected cases of TB across various ethnic groups has not yet been reported. In addition to further quantify TB infection in the UK white population, this study also looked at IGRA positivity in the elderly population.

Methodology Retrospective study of IGRAs which were performed in cases where latent or active TB was suspected. Data were collected from regional IGRA database and individual hospital audit departments were approached to obtain ethnicity data.

Results Ethnicity data was available in 575/1119 cases and comprised 482 white British, 26 Asian/Asian British, 34 black/black British and 33 other. IGRAs results in the UK population are shown in the Abstract P16 table 1 below: The difference in the prevalence of a positive IGRA between the ethnic groups was statistically significant (p<0.001). Further age specific analysis was performed for the white British population for whom age data was available. Of these 468/482 cases, 47% were male (222/468) and the mean age was 50 years. The study demonstrated a significant association between age upon the occurrence of a positive IGRA result (p<0.001). The likelihood of a positive IGRA result was found to increase for older subjects. In the Mersey region, for the UK white population aged =65, the prevalence of a positive IGRA result was between 18% and 37% (95% CI).

Abstract P16 Table 1

Conclusions IGRA positivity was found to be lowest in the white British population compared with other ethnic groups. Interestingly, of the UK indigenous white elderly population almost 1/3 are infected with TB (latent or active) highlighting significant disease burden among older age groups. With IGRAs heralded as the more specific and reliable diagnostic test, such results may aid future planning and policy making for the management of TB in the UK.

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