Study setting and design.
Zambia is a landlocked country in the Southern African continent with a total surface area of 752,612 square kilometres. The country shares common boundary with Democratic Republic of the Congo in the north, Tanzania in the northeast, Malawi in the east, Mozambique in the southeast, Zimbabwe and Botswana in the south, Namibia in the southwest, and Angola in the west. Since 2019, Zambia is administratively divided into 10 provinces with 116 districts. The country has a subtropical climate characterized by 3 main seasons: the rainy season (November to April), which is warm and wet; the cold season (May/June to October/ November), which is dry and cold, and the hot season (September to October), which is dry and hot. In this study, we conducted a retrospective descriptive analysis of routinely collected AFP surveillance data from January 2015 to December 2021. All AFP cases that were reported nationwide during this period were included.
Acute flaccid surveillance system in Zambia
Acute Flaccid Paralysis (AFP) Surveillance activities started in the capital Lusaka in 1993 and later scaled up nationwide in August 1998. In the surveillance system, an AFP is defined as “any child <15 years of age presenting with sudden (acute) onset of flaccid (floppy) paralysis or muscle weakness, or any person of any age with paralytic illness whom a clinician suspects poliomyelitis. The AFP case-based surveillance has been adopted as the gold standard and is being conducted via the Integrated Disease Surveillance System (IDSR) by the Ministry of Health (MOH) and coordinated by the Zambia National Public Health Institute (ZNPHI) surveillance and disease control department. There are established surveillance structures at all levels of the health service delivery with community health volunteer/informant at community level, surveillance focal person at health facility level, disease surveillance officer at district level, and provincial surveillance officer at provincial level.
Figure 1 represents the flow of information and feedback mechanism of the AFP surveillance system from the community to national levels. The primary purpose of the AFP surveillance system is to ensure no polio case goes undetected by identifying, reporting, investigating, and collecting stool samples from all AFP cases to test for poliovirus in the national WHO polio accredited laboratory. All AFP cases identified by the community health volunteer or informants (traditional healers, religious leaders) or health facility staff (clinicians or facility focal persons) are reported to the districts disease surveillance officer (DSO) for further verification and validation. The DSO support the facility surveillance focal person (SFP) to fill the AFP case investigation form, collect two adequate stool samples with adequate documentation and transport using the required optimal temperature to the national polio laboratory at the University Teaching Hospital (UTH) in Lusaka. The DSO ensures the AFP sample results are communicated back to the facility and community. At the provincial level, the provincial surveillance officer, or the WHO surveillance officer assigned to that province or the field epidemiology training program trainee under the ZNPHI supports the DSO to conduct AFP case validation and 60-days follow-up evaluations and reports to the national level. At the national level, the ministry of health MOH in collaboration with the ZNPHI and WHO coordinate the reporting and provide the needed information for the national polio expect committee (NPEC) to conduct the final classification of all reported AFP cases.
Measures
Demographic and clinical variables
During AFP case investigation, information including demographic and clinical and vaccination history is collected. In this study data on age (months), sex (male or female), polio vaccination status (vaccinated or not), number of doses received from either the routine or SIAs if vaccinated, fever at onset of paralysis (Yes or No), progression of paralysis within 3 days after onset of paralysis (Yes or No), and nature of the paralysis (asymmetric or symmetric) were extracted from the existing polio database for analyses.
Surveillance performance indicators
The WHO established minimum performance indicators that are used to assess and maintain the quality of AFP surveillance system13 18. In this study, we evaluated the performance of the surveillance system using the WHO-specified indicators as follows:
Non-polio acute flaccid paralysis (NP_AFP): this refers to number of AFP cases <15 years that are not due to polio per 100,000 population age <15 years. The recommended target is 2 per 100,000 population of <15 years in endemic regions and is 3 per 100,000 population of <15 years in outbreak areas. This indicates that the AFP surveillance system is sensitive13 18.
Stool adequacy: This refers to the proportion of AFP cases with two adequate stool samples (≥8 grams) collected in 24-48 hours apart within 14 days after onset of paralysis, transported on ice/frozen packs and arrive in the laboratory in a good condition. The recommended target is ≥80%13 18.
Timely AFP case notification: This refers to the interval between the onset of paralysis and the notification of the AFP case to the district or facility level surveillance team. The recommended standard is ≥80% of cases should be notified within 7 days of onset of paralysis to assist prompt public health actions to prevent further transmission of poliovirus13 18.
Timely investigation of AFP cases: this refers to the time interval between AFP case notification and investigation by the surveillance team. It is recommended that ≥80% of AFP cases should be investigated within 48 hours of notification13 18.
Timely arrival of stool samples in WHO accredited laboratory: This refers to the proportion of AFP cases stool samples arriving in the laboratory within 3 days of collection of second stool sample. The recommended target is ≥80%13 18.
Arrival of stool sample in the laboratory in a good condition: the refers to the proportion of stool samples that arrive in the laboratory in the temperature range of +2 °C to +8 °C, with no spillage/desiccation and with the appropriate documentation. The recommended target is ≥80%13 18.
Completeness of follow-up: this refers to the proportion of AFP cases with a follow-up evaluation for residual paralysis 60-days after onset of paralysis. The recommended target is ≥80%13 18.
Data source and analysis
We extracted this study data from the WHO Polio Information System (POLIS) 2022 dashboard. The POLIS platform allows countries to load, clean and harmonize polio surveillance data at sub-national, national, and regional levels for decision making. Data from January 2015 to December 2021 was extracted in a Microsoft comma separated values (Ms csv) file formats which included all key demographic, clinical, vaccination, and polio surveillance variables. The data was then compared with the country level Access database for consistency and quality checks.
We then conducted descriptive statistical analysis using Microsoft Excel (version 2021) spreadsheet for key polio surveillance indicators. Maps were developed using Quantum Geographical system (QGIS) version 2.18.10 to visualise the key surveillance indicators performance at the provincial and district levels. Findings of the study were presented using tables, charts, and maps. All outcome parameters were based on the WHO recommended performance indicators of AFP surveillance13 18.