Mapping disease in urban informal settlements: A priority for slum health

Background: With the imminent countdown to the 2015 MDG, policy makers and researchers will need to redefine new goals in the context of technologies increasingly available to developing nations. One such technology is geographic information systems (GIS). In this context, we review recent experiences of mapping Staphylococcus aureus (SA) colonization and tuberculosis (TB) cases in Brazilian slums to review inherent difficulties in mapping cases in these communities and present in-context approaches to overcoming them.

Methods: Residential addresses of cases from two previous studies conducted in Rio de Janeiro were used to demonstrate feasibility of mapping cases within slums. The first dataset consisted of 500 children attending day care centers with addresses verbally reported and individually geocoded. The second dataset included all TB cases reported (n=13,915) to the Brazilian National Reportable Disease Surveillance System in 2010 with addresses batch geocoded.

Results: For children addresses, 71.6% were georeferenced to at least the street or address level. National reportable disease data was found to have a higher geocoding success rate (99.1%) given neighborhood was designated. Cases clustered along the borders of slum boundaries.  Many slum dwellers used a collective address located just outside the slum; street numbers are only available until the slum limits. 

Conclusions: Currently, retrospective mapping of slum communities by address is mainly useful at the aggregate level of slum versus non-slum classification. This designation allows public health officials to better quantify health disparities, particularly in the case of middle-income countries with extreme contrasts between rich and poor populations.