Contributions of AFP Contact Samples to the Sensitivity of the AFP Surveillance System in South-Sudan, 2012-2016

Background: South Sudan continues to witness recurrent conflicts, with the attendant risk of polio outbreaks in the country. For AFP surveillance, one stool specimen is required from at least three healthy children who made direct contact with an index AFP cases. This paper evaluates the contribution of contact sampling to the sensitivity of the AFP surveillance system in South-Sudan. Method: This was a retrospective cohort study carried out in all states in South Sudan using the country's AFP surveillance dataset as at 2016. Results: A total of 4687 contacts were identified for 1637 index AFP cases. Lakes (740) and Western Equitoria (700) provinces recorded the highest numbers of children contacts while Unity (200) and Central Equitoria (272) provinces recorded the least. Proportion of children with zero OPV exposure amongst the index AFP cases was lowest in 2013 (1.7%) and highest in 2015 (3.7%). Amongst the AFP contact cases, the proportion of children with zero OPV exposure was highest in 2016 (2.0%) and lowest in 2013 (0.6%). About 5.3% and 2.9% of the children in the 0-1 year age bracket for both index AFP and contact cases received zero exposure to OPV while 76.9% and 76.5% of the children in the aforementioned age bracket had received three or more does of OPV. NPEV isolation rate stood at 19.4% and 15.1% for both AFP and contact cases respectively. Conclusion: The collection of stool samples from contacts with index AFP cases has given the AFP surveillance system in South-Sudan added capacity to detect polioviruses. However, we recommend improved AFP case reporting and RI delivery services, particularly to the children in the 0-1 year age group.