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DATA BRIEFS (continued)

Knowing the enemy: Polio surveillance systems

Between 1988 and 1998, the number of confirmed polio cases fell from 35,251 to 5,108, bringing the world close to eradicating a communicable disease for only the second time in history. But 50 countries still lack functional polio surveillance systems and, as of the end of 1998, only 7 countries in Africa had surveillance systems that could be considered fully adequate. Significantly, however, India, which alone accounts for 70% of the confirmed polio cases in the world, achieved a functioning surveillance system in 1998.

Adequate polio surveillance systems are a world goal for the year 2000, and to help reach it, the international community's attention will be focused on 13 countries where polio still spreads freely. These 13 countries, which represent the biggest reservoir of polio in the world, account for 92% of all confirmed cases reported in 1998.

Surveillance systems are essential to eradicate polio, as every case of infection-related paralysis must be identified and then investigated in a laboratory. When polio is suspected, stool samples should be collected within 48 hours of the onset of symptoms and then transported to the nearest lab in time to allow testing for the live virus. If polio is found, follow-up tests are done by regional laboratories. The patient receives a complete follow-up exam within 60 days of onset to test for residual paralysis.

If the cause of the paralysis is in fact polio, it must be determined whether it is a wild (indigenous or imported) or a mutated vaccine strain of the virus. Knowing the strain is important, because a country can be considered polio-free only when it has had no cases of wild-virus polio for three consecutive years.

Also, when health officials know the origin of the strain they can respond appropriately, with either a new immunization programme or a door-to-door 'mop up' vaccination campaign.

There are 134 laboratories around the world that test all suspected polio cases. As of this writing, 107 of them have been assessed and 89 of them have been fully accredited.