Polio epidemiology and demographics
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]
Overview
Because of polio eradication efforts, the number of countries where travelers are at risk for polio has decreased dramatically. The last documented case of wild polio virus-associated paralysis in a US resident traveling abroad occurred in 1986 in a 29-year-old vaccinated adult who had been traveling in South and Southeast Asia. In 2005, an unvaccinated US adult traveling abroad acquired vaccine-associated paralytic poliomyelitis after contact with an infant recently vaccinated with oral polio vaccine.
Prevalence
- In the immediate prevaccine era, improved sanitation led to less frequent exposure and increased the age of primary infection. Boosting of immunity from natural exposure became more infrequent, and the number of susceptible persons accumulated, ultimately resulting in the occurrence of epidemics, with 13,000 to 20,000 paralytic cases reported annually.[1]
- Since the GPEI (Global Polio Eradication Initiative) was launched in 1988, the number of cases has fallen by over 99%. In 2014, only 3 countries in the world remain polio-endemic: Nigeria, Pakistan and Afghanistan.[2]
Incidence
- Poliomyelitis cases have decreased by over 99% since 1988, from an estimated 350 000 cases in more than 125 endemic countries then, to 406 reported cases in 2013. These included only 160 cases in endemic countries; international spread from endemic areas into poliomyelitis-free areas accounted for the remainder.[2]
- In 2009, only 1,579 confirmed cases of poliomyelitis were reported globally and poliomyelitis was considered endemic in only four countries.[1]
Age
- Poliomyelitis mainly affects children under 5 years of age.[2] However, the death-to-case ratio for paralytic poliomyelitis is generally 2-5% among children and up to 15-30% for adults (depending on age).[3]
Gender
- The prevalence and incidence of poliomyelitis does not vary by gender.
- The female gender has increased risk of developing "postpolio syndrome".
Race
Developed Countries
- Poliomyelitis reached a peak in the United States in 1952, with more than 21,000 paralytic cases. However, following introduction of effective vaccines, poliomyelitis incidence declined rapidly. A poliomyelitis eradication program conducted by the Pan American Health Organization led to elimination of polio in the Western Hemisphere in 1991.
- The Global Polio Eradication Program has dramatically reduced poliovirus transmission throughout the world. The last case of wild-virus poliomyelitis acquired in the United States was in 1979, and global polio eradication may be achieved within the next decade.[1][3]
- Since 1991, when the last wild-virus-associated indigenous case was reported from Peru, no additional cases of poliomyelitis have been confirmed despite intensive surveillance. In September 1994, an international commission certified the Western Hemisphere to be free of indigenous wild poliovirus. [3]
Developing Countries
- In 2014, only parts of 3 countries in the world remain endemic for the disease - the smallest geographic area in history. Of the 3 strains of wild poliovirus (type 1, type 2, and type 3), wild poliovirus type 2 was eradicated in 1999, and case numbers of wild poliovirus type 3 are down to the lowest-ever levels with the last case reported in November 2012 from Nigeria.[2]
References
- ↑ 1.0 1.1 1.2 "Poliomyelitis".
- ↑ 2.0 2.1 2.2 2.3 "Poliomyelitis".
- ↑ 3.0 3.1 3.2 "Poliomyelitis" (PDF).