Notifications in cases of gonorrhoea, chlamydia and syphilis saw a 39 per cent decrease last week, compared with the previous seven days.

But the medical director of Queensland Health's STI unit, Alun Richards, said that was not evidence of a lack of romance or couples having safer sex.

“Just because the numbers decreased that week doesn’t necessarily mean there was more safe sex going on in that week."

He said an infection could take any time from a couple of days to months to develop.

“Results of that particular week could come in over a three-month period,” Dr Richards said.

“There is rarely any reasons we can find for why variation occurs week-to-week other than if there are fewer people testing because of public holidays."

Dr Richards said the unit did not pay much attention to weekly variations, instead focusing on long-term trends.

And those trends show STIs are on the rise.

More than 23,000 Queenslanders were diagnosed with chlamydia last year and almost 5000 with gonorrhoea.

Yet almost a third of Queenslanders aged 15 to 29 had hardly ever used condoms, according to Queensland Health.

Research showed most young people had never been tested for an STI because they were too embarrassed to talk to a health professional or because they didn’t believe they were at risk.

Dr Richards said a popular myth was people believed they were safe from infections because their partner did not look like someone who would have a sex infection.

"STIs can be acquired by people whatever they look like. You cannot tell if someone has HIV or hepatitis just by looking at them or even when you are having sex with them," he said.

STIs often don't show symptoms.

"The reality is the numbers are increasing, there are quite a lot of STIs out there at the moment and it is important for people to take precautions to protect themselves."

He said condoms and water-based lubricants were the best defences against infections and people who were having sex needed to be checked at least once a year or every time they had a new partner, even if they did not have any symptoms.