Reply #48: Here's what the CDC says about the overall national numbers

[HamdenRice]

But before that, I just should note that 13% (your number) is still in the same ball park as 16% (1 in 6).

That said, all this is inferring from multiple broad demographic sources, while the CDC simply tests people in a variety of medical settings, adjusts the data and comes up with broad demographic figures, which seems much more accurate than what we can speculate about on a discussion board. The CDC fact says the following (sorry, but this site immediately jumps to a pdf; just click stop on your browser to read the html):

http://www.cdc.gov/hiv/topics/msm/resources/factsheets/msm.htm

In the United States, HIV infection and AIDS have had a tremendous effect on men who have sex with men (MSM). MSM accounted for 71% of all HIV infections among male adults and adolescents in 2005 (based on data from 33 states with long-term, confidential name-based HIV reporting), even though only about 5% to 7% of male adults and adolescents in the United States identify themselves as MSM <1, 2>.

The number of HIV diagnoses for MSM decreased during the 1980s and 1990s, but recent surveillance data show an increase in HIV diagnoses for this group <3, 4>. Additionally, racial disparities exist with regard to HIV diagnoses within the MSM population. A recent study, conducted in 5 large US cities, found that HIV prevalence among black MSM (46%) was more than twice that among white MSM (21%) <5>.
...
HIV/AIDS in 2005
(The following bullets refer to the 33 states with long-term, confidential name-based HIV reporting. See the box, before the References section, for a list of the 33 states.)

* In the 33 states with long-term, confidential name-based HIV reporting, an estimated 19,620 MSM (18,296 MSM and 1,324 MSM who inject drugs) received a diagnosis of HIV/AIDS, accounting for 71% of male adults and adolescents and 53% of all people receiving an HIV/AIDS diagnosis that year <1>.
* The number of HIV/AIDS diagnoses among MSM (including MSM who inject drugs) increased 11% from 2001 through 2005 <1>. It is not known whether this increase is due to an increase in the testing of persons with risk factors, which results in more HIV diagnoses, or due to an increase in cases of HIV infection
...
Unknown HIV Serostatus
Approximately 25% of people in the United States who are infected with HIV do not know they are infected <14>.

* Through its National HIV Behavioral Surveillance system, CDC found that 25% of the MSM surveyed in 5 large US cities were infected with HIV and 48% of those infected were unaware of their infections <5>.
* In a recent CDC study of young MSM, 77% of those who tested HIV-positive mistakenly believed that they were not infected <15>. Young black MSM in this study were more likely to be unaware of their infection―approximately 9 of 10 young black MSM compared with 6 of 10 young white MSM. Of the men who tested positive, most (74%) had previously tested negative for HIV infection, and 59% believed that they were at low or very low risk.