Polio eradication surveillance in Sri Lanka, 2019-2023

Abstract

Objective: To evaluate the polio laboratory surveillance carried out from January, 2019 to May, 2023 by the Polio Regional Reference Laboratory, Sri Lanka. Methods: This retrospective study analyzed all stool samples received under the acute flaccid paralysis (AFP) and immunodeficient vaccine-derived poliovirus (VDPV) surveillance at Polio Regional Reference Laboratory, Sri Lanka from January, 2019 to May, 2023. The results of the testing methodologies were extracted from the laboratory data system, i.e., poliovirus virus isolation, intra-typic differentiation/VDPV real time reverse transcriptase polymerase chain reaction (ITD/VDPV rRTPCR) and sequencing, along with the data on timing of reporting results, stool adequacy and socio-demographics. Data was analyzed using descriptive statistics. Results: A total of 2141 stool samples from 1 644 cases were received for AFP surveillance from Sri Lanka (93.61%), Maldives (1.52%), and immunodeficient VDPV (4.86%) surveillance. Both polioviruses (19/1 644, 1.15%) and non-polio enteroviruses (73/1 644, 4.44%) were isolated, while Sabin-like 3 virus was detected in majority (12/19, 63.15%) among the poliovirus isolated. Wild polioviruses or circulating VDPVs were not detected among the cases. During all years of the study, the non-polio AFP detection rate was >1/100 000 in children aged less than 15 years, whereas stool adequacy rate was >80%. All results were reported within 14 days of receipt, ensuring timely reporting as per global guidelines. Conclusions: The Polio Regional Reference Laboratory, Sri Lanka plays a vital role in maintaining the polio-free status in the country through its robust laboratory surveillance, while adhering to the surveillance indicators. Non-detection of wild polioviruses and circulating VDPV during the study period reinforces the polio-free status in the country.