One in two gay and bisexual black men in the US will be diagnosed with HIV in their lifetime, according to the Centers for Disease Control and Prevention.

In contrast, one in four gay and bisexual Hispanic men are at risk of being diagnosed - and one in 11 gay and bisexual white men.

In contrast, the overall lifetime risk of an average American being diagnosed as HIV positive is one in 99 - down from around one in 78 a decade ago.

According to the CDC, a number of factors may contribute to the higher risk HIV risk associated with gay and bisexual black men.

Those factors include socioeconomic circumstances – such as limited access to quality health care and higher levels of unemployment – smaller sexual networks and lack of awareness of HIV status.

Dr Eugene McCray, director of CDC's Division of HIV/AIDS Prevention, said: 'These estimates are a sobering reminder that gay and bisexual men face an unacceptably high risk for HIV – and of the urgent need for action.

'If we work to ensure that every American has access to the prevention tools we know work, we can avoid the outcomes projected in this study.'

The estimates come from the CDC's first comprehensive national estimates of the lifetime risk of HIV diagnosis for several at risk populations - and in every state.

Dr Jonathan Mermin, of the CDC, said: 'As alarming as these lifetime risk estimates are, they are not a foregone conclusion. They are a call to action.

'The prevention and care strategies we have at our disposal today provide a promising outlook for future reductions of HIV infections and disparities in the US.

'But hundreds of thousands of people will be diagnosed in their lifetime if we don’t scale up efforts now.'

In the report, the CDC offers an overview of HIV infections.

The agency calculated its estimates from HIV diagnoses and death statistics from 2009 and 2013.

The CDC's previous estimate was only based on 33 states, while the new report covers all 50 states, as well as the District of Columbia. 

That's why, for the first time, the agency was able to calculate lifetime risk for specific groups - and for each individual state.

The overall HIV rate is declining, but the risk of HIV infection varies heavily among different groups.

For instance, while the projection for gay black men is one in two, it is less than one in 2,500 for heterosexual white men.

Dr Mermin, of the CDC, told the Associated Press: 'The differences are stark.'

Human immunodeficiency virus - or HIV - is primarily spread through sex or sharing needles used to inject drugs. 

Infections in the US are most common in men who have sex with men.

HIV leads to AIDS - or acquired immunodeficiency syndrome, which was first identified over 30 years ago.

But in the past 30 years, medicines have transformed AIDS from a death sentence into a 'chronic threat.'

The CDC found that new HIV infections have fallen in the US to nearly 40,000 annually. 

Yet, close to 10,000 of those cases occur in gay and bisexual black men.