Background Expanding delivery of primary health care to urban poor populations is a priority in many low-and middle-income countries. This remains a key challenge in Brazil despite expansion of the country’s internationally recognised Family Health Strategy (FHS) over the past two decades. This study evaluates the impact of an ambitious program to rapidly expand FHS coverage in the city of Rio de Janeiro, Brazil since 2008. Methods and Findings A cohort of 1,241,351 million low-income adults (observed January 2010-December 2016; total person-years 6,498,607) with linked FHS utilisation and mortality records was analysed using flexible parametric survival models. Time-to-death from all-causes and selected causes were estimated for FHS users and non-users. Models employed inverse probability treatment weighting and regression adjustment (IPTW-RA). The cohort was 61% female (751,895) and had a mean age of 36 years (standard deviation 16.4). Only 18,721 individuals (1.5%) had higher education whilst 102,899 (8%) had no formal education. Two-thirds of individuals (827250; 67%) were in receipt of conditional cash transfers (Bolsa Família). A total of 34,091 deaths were analysed of which 8,765 (26%) were due to cardiovascular disease, 5,777 (17%) due to neoplasms, 5,683 (17%) due to external causes, 3,152 (9%) due to respiratory diseases, and 3,115 (9%) due to infectious and parasitic diseases. One third of the cohort (467,155; 37.6%) used FHS services. In IPTW-RA survival analysis, an average FHS user had a 44% lower hazard of all-cause mortality (HR: 0.56, 95%CI: 0.54 to 0.59, p<0.001) and a five-year risk reduction of 8.3 per 1000 (95%CI: 7.8 to 8.9, p<0.001) compared to a non-FHS user. There were greater reductions in the risk of death for FHS users who: were black (HR:0.50 (95%CI: 0.46 to 0.54, p<0.001)) or pardo (HR:0.57 (95%CI: 0.54 to 0.60, p<0.001) compared to white (HR:0.59 (95%CI: 0.56 to 0.63, p<0.001); had lower educational attainment (HR:0.50 (95%CI: 0.46 to 0.55, p<0.001) for those with no education compared to no significant association for those with higher education (p=0.758)); or were in receipt of conditional cash transfers (Bolsa Família) (HR:0.51 (95%CI: 0.49 to 0.54, p<0.001) compared to HR:0.63 (95%CI: 0.60 to 0.67, p<0.001) for non-recipients). Key limitations in this study are potential unobserved confounding through selection into the programme and linkage errors, although analytical approaches have minimized the potential for bias. Conclusions FHS utilisation in urban poor populations in Brazil was associated with a lower risk of death, with greater reductions among more deprived ethnic and socio-economic groups. Increased investment in primary health care is likely to improve health and reduce health inequalities in urban poor populations globally
