Full Text
The Full Text of this article is available as a PDF (43.0 KB).
letter . 1999 Apr;53(4):256. doi: 10.1136/jech.53.4.256
Official websites use .gov
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.