Polio AFP surveillance — DTM&H MCQ
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Correct answer: A — 2 per 100,000
The correct answer is A, 2 per 100,000. WHO's Global Polio Eradication Initiative defines the non-polio AFP (NPAFP) rate as the core sensitivity indicator for AFP surveillance systems, and in countries at risk of, or affected by, poliovirus transmission (such as Nigeria), the minimum acceptable annual rate is at least 2 non-polio AFP cases per 100,000 children under 15 years. This threshold reflects the expected background incidence of AFP from non-polio causes (Guillain-Barre syndrome, transverse myelitis, traumatic neuritis, other enteroviruses) and confirms the system is sensitive enough to detect a true poliovirus case if one were circulating. A cluster of 3 AFP cases within 2 weeks in one area is itself an alert requiring urgent case-based investigation, but the benchmark being tested here is the standard annual surveillance sensitivity target, which is 2 per 100,000 under-15s, not a rate derived from the cluster size itself. Why the other options are wrong: A, 1 per 100,000: this is the target only for regions certified polio-free with no ongoing risk, not for an at-risk or endemic country like Nigeria. B, 20 per 100,000: this figure is far higher than any WHO benchmark and does not correspond to any recognised AFP surveillance indicator. C, 5 per 100,000: not a WHO-defined surveillance threshold; it overstates the minimum requirement and is not used in GPEI guidance. D, 10 per 100,000: similarly not a recognised WHO target; it would represent an unrealistically demanding minimum for routine surveillance sensitivity. Key point: in polio at-risk or endemic countries, WHO requires a minimum non-polio AFP rate of at least 2 per 100,000 children under 15 years annually to confirm surveillance is sensitive enough to detect poliovirus transmission.
Reference: WHO/GPEI, Global Guidelines for Acute Flaccid Paralysis (AFP) Surveillance (2023 pre-publication version): non-polio AFP rate target of at least 2 per 100,000 children under 15 years in at-risk and outbreak-affected countries. https://polioeradication.org/wp-content/uploads/2023/03/Global-AFP-guidelines-pre-publiucation-version-2023.pdf