Introduction On 4 November 2010, the Ministry of Health of the Republic of Congo declared a poliomyelitis outbreak in Pointe-Noire, the eastern economic capital. We conducted an outbreak investigation to describe the epidemic and estimate vaccination coverage to better understand virus spread.

Methods We collected clinical, demographic and geographic data about cases and vaccination policies from local health authorities. Cases were defined as residents of Pointe-Noire of any age, diagnosed with acute flaccid paralysis since 1 October 2010. We implemented a cross-sectional survey in a socially heterogeneous affected neighbourhood (representing 9.5% of the city population), selected from the Loandjili district (highest district attack rate: 71.6 cases per 100 000) following expert consultation.

Results From 1 October to 20 December 2010, 446 cases of acute flaccid paralysis were reported to health authorities (case fatality ratio: 41.3%). Males accounted for 68% of the cases, and 57.4% were between 15 and 24 years of age. Vaccination coverage in the surveyed population for one or more doses of oral polio vaccine was 55.5% on average and decreased with age to 33.5% for individuals older than 30. Sanitary conditions were poor to medium with latrines commonly shared between households (57.4%).

Conclusion Poor vaccination coverage led to a large susceptible population, particularly in young adults and spread was further facilitated by poor sanitary conditions. Moreover, polio causes more severe clinical symptoms among older age groups, which explains the high case-fatality ratio. To prevent similar outbreaks in other countries, supplementary vaccination activities should punctually target older age groups.