Case definition: Poliomyelitis
Adapted from Epidemiological Bulletin, Vol. 20 No. 2, June 1999
- Rationale for Surveillance
- Recommended Case Definitions
- Recommended Surveillance Measures
- Recommended Minimum Data Elements
- Principal Use of Data for Decision-Making
- Surveillance Indicators for Certification
Rationale for Surveillance
Targeted for eradication (item 6.1 of the WHO General Program of Work, 9GPW6.1) and although eradicated in the Americas, this disease requires highly sensitive surveillance for acute flaccid paralysis (AFP), including immediate case investigation and the specimen collection, which are critical to detect wild poliovirus circulating in every infected geographical area. A polio eradication program should use the following standardized case definitions, revised from the PAHO's Polio Eradication Field Guide, 2nd. Ed., 1994, and the WHO Recommended Surveillance Standards from the 2nd. Ed., June 1999, revised by the PAHO's Communicable Diseases Program.
Recommended Case Definitions
Suspected case: any case of acute-onset flaccid paralysis (AFP), including Guillain-Barré syndrome, in a person under 15 years of age for any reason other than severe trauma, or paralytic illness in a person of any age in which polio is suspected. The classification "suspected case" is temporary. It should be reclassified as "probable" or "discarded" within 48 hours of notification.
Probable case: a case in which AFP is found, and no other cause for the paralysis can be identified immediately. The classification of "probable case" is also temporary; within 10 weeks of onset the case should be reclassified as "confirmed", "compatible", "vaccine-associated" or "discarded."
Confirmed case: a case with acute paralytic illness, with or without residual paralysis, and isolation of wild poliovirus from the stools of either the case or its contacts.
Polio-compatible case: a case in which one adequate stool specimen was not collected from a probable case within 2 weeks of the onset of paralysis, and there is either an acute paralytic illness with polio-compatible residual paralysis at 60 days, or death takes place within 60 days, or the case is lost to follow-up.
Vaccine-associated Paralytic Poliomyelitis case: a case with acute paralytic illness in which vaccine-like poliovirus is isolated from stool samples, and the virus is believed to be the cause of the disease. There are two possible types of vaccine-associated paralytic poliomyelitis (VAPP): recipient and contact. A case classified as a recipient is a person who has onset of AFP 4 to 40 days after receiving OPV and has neurologic sequelae compatible with polio 60 days after the paralysis began. A case is classified as a contact VAAP when a person who has residual paralysis 60 days after the onset of AFP had contact 4 to 40 days before the paralysis began with a person who received OPV somewhere between 4 and 85 days before the contact's paralysis began.
Discarded (Not Poliomyelitis) case: a case with acute paralytic illness for which one adequate stool specimen was obtained within 2 weeks after onset of paralysis and was negative for poliovirus.
Recommended Surveillance Measures
- The reporting system must cover key hospitals and clinics and have at least one reporting source for every geopolitical unit;
- The concept of reporting all AFP cases rather than only poliomyelitis cases must be emphasized;
- Weekly reporting of AFP is critical;
- The concept of negative reporting of AFP must be included in the weekly reporting system;
- The reporting system for AFP must continually be monitored and revitalized;
- Immediate response to reports in the surveillance system by trained epidemiologists must occur for every suspected case within 48 hours;
- Cooperation from the private medical community is essential for all surveillance efforts;
- The public needs to be informed about the importance of and procedure for reporting AFP;
- Feedback to all participants of the surveillance system is essential.
Recommended Minimum Data Elements
Case-based data (to be linked to specimen-based data for analysis): (i) unique identifier; (ii) geographical area (district and province) name; (iii) date of birth; (iv) date of onset of paralysis; (v) date of notification; (vi) date of case investigation; (vii) total poliomyelitis vaccine doses received; (viii) fever at onset of paralysis; (ix) progression of paralysis within 4 days; (x) asymmetric paralysis; (xi) date of 60-day follow-up examination; (xii) findings at 60-day follow-up; (xiii) final classification.
Specimen-based data (to be linked to case-based data for analysis): (i) unique identifier; (ii) specimen number; (iii) date of paralysis onset; (iv) date of last OPV; (v) date of stool specimen collection; (vi) date stool specimen sent to laboratory; (vii) date specimen received in laboratory; (viii) condition of stool; (ix) date final culture results sent from laboratory to EPI; (x) date intra-typic differentiation results sent from laboratory to EPI; (xi) results of stool samples.
Principal Uses of Data for Decision Making
- One polio case must be considered as an outbreak.
- Track wild poliovirus circulation.
- Classify cases as confirmed, poliomyelitis compatible or discarded.
- Monitor routine coverage for immunizations in all geographical areas and focus efforts in low performing geographical areas.
- Identify high-risk areas for planning mop up immunization.
- Monitor performance of surveillance using standard indicators and focus efforts in low performing areas.
- Provide evidence for polio-free certification.
- Conduct two National Immunization Days (NIDs) a year in countries with < 80% of districts with OPV3 > 95%.
Surveillance Indicators for Certification
- AFP rate per 100,000 children < 15 years of age.
- % AFP cases with one stool taken within 15 days of paralysis onset.
- % AFP cases investigated within 48 hours of notification date.
- % of reporting sites registered each week.
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