The two groups most affected in the UK are men who have sex with men (MSM) and black African heterosexual men and women.
Approximately 3,360 MSM (men who have sex with men) were diagnosed in 2014, 55% of the total. This was the highest number ever reported - the largest proportion of cases - and gay men are still the highest-risk group for HIV within the UK. In 2014 approximately three quarters (76%) of newly diagnosed MSM probably acquired HIV in the UK.
A similarly large proportion of people diagnosed with HIV in the UK in 2014 (40%) were infected through heterosexual sex. In 2014, 37% of newly diagnosed heterosexual people were aged 45 years or above. Approximately half of those infected heterosexually were black African.
Looking at probable country of infection, 59% of all heterosexuals diagnosed acquired HIV in the UK. However the absolute number of new diagnoses of UK-acquired infections has dropped from approximately 1,700 to 1,500 (2005-2014).
The proportion of new diagnoses among people born in Africa has decreased from 44% of total diagnoses in 2005, to 20% in 2014. The number of new diagnoses reported in this group has more than halved since 2004.
Needle exchange and harm reduction programmes have been very effective and new diagnoses of HIV infection acquired through injecting drug use (150 in 2014) have remained low.
It is also possible for the virus to be passed from mother to baby during pregnancy but improvements to antenatal HIV testing and treatments make this increasingly rare.
In the past, some people also got HIV through blood products but in the UK this is now extremely rare. Since the introduction of testing for HIV in 1985, there have been three cases of transmission of the virus to patients through blood from donors, and none since 2002.