Components of AFP Surveillance

WHO indicators of AFP surveillance and laboratory performance:

1. Non-polio AFP rate in children < 15 years of age. (Target > 1/100,000)

Non-Polio AFP Rate =

Number of reported non-polio AFP cases < 15 years of age x 100,000 Total number of children < 15 years of age

The non-polio AFP rate is an indicator of surveillance sensitivity. If it is < 1/100,000 then the surveillance system is probably missing cases of AFP.

2. Completeness of weekly “zero” reporting. (Target >90%)

% Complete =

Number of Weekly reports received x 100% Number of Weekly reports expected

3. Timeliness of weekly “zero” reporting. (Target > 80%)

% timely =

Number of weekly reports received before a specified deadline X100% Number of weekly reports expected

4. Reported cases investigated < 48 hours of report (Target > 80%)

Every reported case of AFP is a public health emergency to be investigated by a trained, designated case investigator within 48 hours of receiving the report.

5. Reported AFP cases with 2 stool specimens collected < 14 days since paralysis onset (Target > 80%)

6. Reported AFP cases with a follow-up exam at least 60 days after paralysis onset to verify the presence of residual paralysis or weakness (Target > 80%).

AFP cases that should undergo 60-day follow-up include a) cases with inadequate or no stool specimens; b) cases with isolation of vaccine virus from the stool; c) cases with isolation of wild poliovirus from the stool; and d) any case that the investigator thought was strongly suggestive of poliomyelitis on initial examination (“hot case”).

7. Specimens arriving at the national laboratory < 3 days of being sent (Target > 80%)

8. Specimens arriving at the laboratory in “good condition” (Target > 80%)

“Good condition” means that upon arrival:
· there are frozen ice packs or ice, or a temperature indicator (showing < 8° C) in the container
· the specimen volume is adequate (> 8 grams)
· there is no evidence of leakage or desiccation
· appropriate documentation (laboratory request/reporting form) is completed

9. Specimens with a turn-around time < 28 days (Target > 80%)

The turn-around time is the time between specimen receipt and reporting of results

10. Stool specimens from which a non-polio enterovirus is isolated (Target > 10%)

This is an indicator of the quality of the “reverse cold chain” (i.e. that the specimen has been continuously maintained at temperatures <8° C during transportation from the field to the laboratory) and how well the laboratory is able to perform routine isolation of enteroviruses.

Source: Field guide for supplementary activities aimed at achieving polio eradication. Global Programme for Vaccines and Immunization, Expanded Programme on Immunization. World Health Organization, Geneva 1997