Research suggests around half of new cases of HIV in the north-west of England were contracted abroad.
According to figures released by the Health Protection Agency in conjunction with the Centre for Public Health at Liverpool John Moore's University, 42% of sufferers contracted the disease and brought it into the country, and of these, 74% were black Africans.
The data from 2008 shows a rise in the number of HIV carriers, with the total number of people in treatment reaching 5,767, 11% more than 2007 when the number was 5,212.
The findings also show there was an increase in the number of people reporting the disease, with 925 cases new to the monitoring system in 2008, up from 817 in 2007.
Professor Qutub Syed, director of the Health Protection Agency North West, said: "It is encouraging that more people with HIV infection are seeking treatment and care, but hugely disappointing that we are seeing an increase in new cases, reversing recent trends.
"This would seem to imply that more people are putting themselves and their partners at risk by failing to be careful about their lifestyles."