Spatial clustering of pulmonary tuberculosis and impact of the care factors in Antananarivo City

To analyse the spatial distribution of TB in Antananarivo and investigate risk factors. Pulmonary TB data were collected through passive case detection in 16 Tuberculosis Diagnostic and Treatment Centers (DTC). New cases listed in the DTC registers from 2004 to 2006 and resident in Antananarivo were included in the study. Field workers of the national control program conducted household surveys of all cases to collect complementary information on socio-economic status. TB spatial organization and risk factors were analysed over two successive periods (August 2004-July 2005, August 2005-July 2006); analysis was done at the neighbourhood level, by searching for spatial clusters with the spatial scan test. 3075 pulmonary tuberculosis new cases were reported in Antananarivo from 2004 to 2006. The average incidence during the study period was 74/100 000 inhabitants (95% CI: 64.9-84.5). Spatial clusters occurred in three of the six arrondissements (districts) of the city (192 neighbourhoods). A decrease in clustering was observed with movement towards the southern neighbourhood. The change in risk of a TB cluster was linked to socio-economic (e.g. household amount of ownership of tap water) and patient care factors (e.g. patients lost to follow-up).