Heterosexual people living in major cities have driven a 63% rise in gonorrhoea in Australia over the past five years.

The data is revealed in the annual surveillance report on HIV, viral hepatitis and sexually transmissible infections, released by the Kirby Institute in Sydney on Monday.

The report shows there were 23,887 new diagnoses of gonorrhoea in 2016, with about three quarters of them in men. Between 2012 and 2016, gonorrhoea notification rates increased from 62 per 100,000 people to 101 per 100,000 people. Rates increased by 72% in men and 43% in women.

Men aged between 25 and 29 and women between 20 and 24 saw the largest increase in gonorrhoea infections, the report found. There was a 99% increase in gonorrhoea notification rates in major cities in the five years to 2016, while rates increased by 15% in regional areas and declined by 8% in rural areas.

Associate professor Rebecca Guy, the head of Kirby’s surveillance evaluation and research program at the University of NSW, said gonorrhoea had been uncommon in young heterosexual urban people until recently. It was unclear why rates were increasing in this population, but it was not because of increasing awareness and diagnosis alone, she said.

There is concern about increasing rates of antimicrobial resistant strains of gonorrhoea, particularly in the US, but Guy said strains in Australia were not resistant yet, so that did not explain the increase either.

“The reasons [for the increase] are not yet understood,” Guy said.

“Changes in sexual behaviour, sociodemographic factors, and the spread of a particular strain in suburban centres may be some of the reasons, even though the specific reasons are not known.”

She said the data suggested doctors should be aware of the need to test patients for the infection, which is asymptomatic in 50% of men and 80% of women. While treatment is simple with antibiotics if caught early, untreated it can cause serious health problems including infertility and sterility.

Chlamydia and gonorrhoea rates were three and seven times higher respectively among Aboriginal and Torres Strait Islander people and the gaps were greater in regional and remote areas, the report found. Since 2011, there has been a resurgence of infectious syphilis among young Aboriginal and Torres Strait Islander people living in regional and remote areas of northern Australia.

The report also found the number of new HIV diagnoses in Australia had remained stable over the past five years, with 1,066 diagnoses in 2012, compared with 1,013 in 2016.

Guy said the results were due to high levels of testing and treatment. “We’re seeing increased uptake of HIV testing, particularly among gay and bisexual men, who are the population most affected by HIV in Australia,” Guy said. “It is also encouraging that 86% of people diagnosed with HIV were on treatment in 2016.”

Those who receive proper treatment can reduce their HIV loads to undetectable levels, eliminating their risk of passing it on.

The surveillance report also found an estimated 30,434 people were cured of hepatitis C between March and December 2016, due to the availability of a new antiviral therapy.

Associate professor Jason Grebely, from the viral hepatitis clinical research program at the Kirby Institute, said the new therapy had been “game-changing”.

“Our estimates indicate that the number of people with hepatitis C who have advanced liver disease has fallen for the first time in 10 years,” he said. “This is excellent news, but to achieve hepatitis C elimination in Australia we must sustain our efforts to ensure all people living with hepatitis C are tested and have access to these cures.”