New figures show the number of HIV cases in the Northern Territory has more than tripled over the past year.

A large proportion of the detected cases involve detainees at Darwin's immigration detention centres.

In its latest bulletin, the Northern Territory Centre for Disease Control says the number of people diagnosed with HIV increased from 11 in 2011 to 36 in 2012.

It says 14 of the new cases involved irregular maritime arrivals sent to immigration detention centres in Darwin.

Some of the other new cases involved immigrants arriving in Australia with HIV, as well as Australians who contracted HIV in countries with a high prevalence of the disease.

The bulletin also says guidelines should be changed so that tourists travelling to Bali receive pre-trip vaccinations for rabies.

The number of people seeking treatment for overseas rabies exposure has increased dramatically in the Northern Territory since 2007.

Back then, just six potential rabies exposures were recorded.

But, in the four years to 2011, a further 86 people sought post-exposure treatment to the dangerous disease.

The vast majority were people who travelled to Bali.

More than half had been bitten or scratched by monkeys there, and a quarter had been bitten by dogs.

The bulletin says the cost of of treating people for rabies post-exposure is more than $2,000 per vaccine, almost 10 times more than if people are vaccinated before their trips.