A .gov website belongs to an official government
organization in the United States.
Secure .gov websites use HTTPS
A lock ( ) or https:// means
you've safely connected to the .gov website. Share sensitive
information only on official, secure websites.
Historical CDC.gov Content
CDC is moving a large quantity of selected historical .PDF files to CDC Stacks. Other selected historical content, including HTML pages, can be found at Archive.CDC.gov at https://archive.cdc.gov/.
Links with this icon indicate that you are leaving the CDC website.
The Centers for Disease Control and Prevention (CDC)
cannot attest to the accuracy of a non-federal website.
Linking to a non-federal Website does not constitute an
endorsement by CDC or any of its employees of the sponsors or the
information and products presented on the website.
You will be subject to the destination website's privacy
policy when you follow the link.
CDC is not responsible for Section 508 compliance
(accessibility) on other federal or private websites.
For more information on CDC's web notification policies, see Website Disclaimers.