Tuberculosis (TB) is the leading cause of death in persons living with HIV (PLHIV) in sub-Saharan Africa and TB incidence is increasing worldwide despite infection control efforts as the two epidemics fuel one another. In Kampala, Uganda, roughly one in four HIV-infected household contacts of TB patients have active TB. Reducing household TB transmission is likely to significantly reduce TB incidence in PLHIV. We hypothesize that household TB transmission is related to poor ventilation. This proposal seeks to describe determinants of ventilation in 200 homes in Kampala with a standardized survey tool, to correlate them to measures of home air exchange rate (AER) using an innovative carbon dioxide (CO2) tracer decay technique, and to conduct a case-control study comparing AER in homes with and without demonstrated TB transmission to determine the impact of ventilation on household TB transmission. Characteristics of the home, the TB index case and the household contacts will be accounted for in our case-control analysis. Home enrollment, surveys and measures will take place over 10 months and analysis over 3 months. Our overall objective is to better understand determinants of household transmission of TB in a resource-limited setting with a high prevalence of TB and HIV. We will use the findings from this pilot project to design and test feasible interventions within individual homes that will reduce TB transmission, particularly among PLHIV.