Efforts in recent years to raise awareness about the HIV virus have helped stem Papua New Guinea's generalised epidemic, according to the National AIDS Council.
The Council's Manager for Research Tony Lupiwa said the epidemic had been downgraded to a concentrated epidemic among key populations in certain provinces, particularly the Highlands.
Mr Lupiwa said the key populations included female sex workers, wealthy businessmen, males who have sex with other males, and transgender people.
The estimated number of people infected in 2016 was 40,000, up from around 25,000 people in 2013.
Suspecting the increase is linked to wider data collection, Mr Lupiwa said the overall situation was improving, but there was still a lot of work to be done.
"We must not become complacent. We have to continue to go out there and make that awareness, and make the condom available to everyone in the community to have access to it, not just condoms, but ART (Antiretroviral Therapy) available to those who are living with HIV."