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Country Classification Technical Guidance

Purpose: To explain how CDC classifies countries based on current or previous Zika transmission or the likelihood of an outbreak in countries that have not had previous Zika transmission. The country classification is used to inform CDC’s recommendations for US citizens and residents who are either traveling to or living in an area where Zika is spreading.

Intended audience: Other USG agencies, ministries of health and other public health partner organizations.

To protect travelers from Zika, scientists and travel experts at CDC are monitoring the status of Zika in countries around the world and making appropriate travel recommendations. These recommendations are based on a number of factors, including the historical or current presence of Zika in the country. Based on this assessment, areas with Zika are classified as epidemic or endemic.

Epidemic: These countries are currently experiencing outbreaks of Zika, and travel notices have been posted to alert travelers, particularly pregnant women, of the risk. These countries are considered epidemic because

  • The mosquito that carries Zika virus is present,
  • Zika has not been reported there in the past, and
  • Very little, if any, of the population is likely to be immune.

When Zika is first introduced into a country, it generally spreads quickly through the population. Over time, as the outbreaks decrease, these countries will change from the “epidemic” to the “endemic” classification, and travel notices will be removed.

Endemic: These countries have reported cases of Zika in the past and may occasionally report new cases. A large number of local residents are likely to be immune, so occasional cases may occur but generally not in numbers large enough to be considered an outbreak. Because the risk to travelers is likely much lower in these countries than in epidemic countries, travel notices will not be posted unless the number of cases rises to the level of an outbreak. For more information, visit Questions and Answers: Zika Risk in Endemic Countries.

Special note about Southeast Asia: Some of these countries have reported cases of Zika in the past, have reported recent variations in the number of cases, or share borders with those countries. Limited information is available to fully evaluate the risk of Zika virus infection in some of these countries. This list might change as we learn more about Zika transmission in Southeast Asia.  Because of this, CDC has issued special travel considerations for these areas.

For general information on countries with endemic Zika, visit Zika Travel Information and Questions and Answers: Zika Risk in Endemic Countries.

Countries that have not reported Zika transmission in the past

Countries that have not previously reported Zika are classified according to the likelihood that they could experience an epidemic. Classification is based on whether or not Aedes aegypti or Aedes albopictus mosquitoes are found in the area and whether or not it has had outbreaks of dengue. Dengue fever is spread by the same types of mosquitoes that spread Zika virus and a history of widespread, recurrent dengue outbreaks indicates that Zika can spread in that same area.

  • Countries that have the Aedes aegypti or Aedes albopictus mosquitoes and a history of widespread, recurrent dengue outbreaks are considered to be at high risk for a Zika epidemic.
  • Countries that have the Aedes aegypti or Aedes albopictus mosquitoes without a history of widespread, recurrent dengue outbreaks are considered to be at low risk for a Zika epidemic.
  • Countries that do not have the Aedes aegypti or Aedes albopictus mosquitoes are not at risk for a Zika epidemic. These countries may still have people who get infected while traveling to a Zika affected area, through sexual transmission, through blood transfusion, or through laboratory exposure.

For example, the contiguous United States is considered to be at low risk for an epidemic because, for many years, we have only had sporadic and focal outbreaks of dengue fever, with no widespread, recurrent outbreaks of dengue fever.

Re-classification of country status

Countries may be re-classified in response to new human and mosquito surveillance data, as well as advancements in the understanding of Zika virus disease and transmission.

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