Three per cent of Washington DC residents suffer from HIV or AIDS – a rate higher than in some African countries such as Uganda.
According to a report from the city’s health department, there has been a 22 per cent increase in rates of the disease since 2006.
Sex among gay men is the leading mode of transmission, accounting for 37 per cent of active cases.
The rates surpass the one per cent benchmark used to judge the point at which a health issue become a “generalised and severe” epidemic.
Fewer than 0.1 per cent of Americans are living with cancer.
The report also suggests that the three per cent figure, which takes into account those over the age of 12, is likely to be unrepresentative as many people will not know they have the disease. Previous research has suggested that between one-third and half of those infected are unaware, meaning the true figure could be closer to five per cent.
It was found that African-Americans are suffering in far greater numbers than other ethnic groups.
More than 75 per cent of residents who have contracted the virus are black, with seven per cent of all black men testing positive. Overall, four per cent of African Americans are afflicted. By contrast, two per cent of Hispanics and one per cent of whites are known to be affected by the virus.
However, the report also suggested that incidents of infection through heterosexual sex and drug use remain high across all ethnic and age groups. Heterosexual sex is the leading transmission cause among African Americans.
City mayor Michael Fenty said the epidemic is “one of the most severe problems” facing the city.
He said: “We know we have a lot of work to do as a government to educate and to get the information out, and as a community to step up and realise how dangerous we are with our sexual behaviour.”