HEALTH professionals are battling an outbreak of sexually transmitted diseases in Mackay, despite residents been forced into coronavirus lockdown.

Mackay Hospital and Health Services reported a dramatic increase in gonorrhoea, syphilis and chlamydia compared to the five-year average.

Gonorrhoea rates were almost four times the year to date average, with 90 cases caught by May 31.

Infectious syphilis rates doubled and 49additional chlamydia cases were reported compared to the five-year average.

Last year 839 people were diagnosed with chlamydia and 170 others found out they had gonorrhoea.

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The spike in venereal disease while residents were meant to be in lockdown has baffled sexual health experts.

"The reason for the increase still remains unclear," Mackay sexual health and sexual assault service nurse practitioner Donna Pini said.

Mackay's suburbs have become a hotspot for the diseases, with Ms Pini saying cases were "prevalent" in the community.

The health service stretches from Mackay to the Whitsundays and out to mining communities like Moranbah, Clermont, Dysart and Middlemount.

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In July 2019 it recorded a sharp increase in gonorrhoea cases and the trend remained unchanged, Ms Pini said.

"High-risk groups for gonorrhoea have been men who had sex with men and Aboriginal and Torres Strait Islander people," she said.

"However, it is now becoming an increasingly urbanised condition and more so in heterosexual Australian caucasians.

"(But), it is too early to say what influence the coronavirus restrictions are having on these trends, which started well before the pandemic."

MHHS is working closely with the Townsville Sexual Health Service to explain the surge in cases.

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But there were simple steps to case numbers from further climaxing.

"Use condoms for STI prevention," Ms Pini said.

"It is important that anyone who is sexually active to be tested for STIs, especially if you have had a new casual partner or recent partner change.

"It is important to remember most STIs are silent and do not produce any symptoms."

Mackay Hospital and Health Service STI rates

Chlamydia: 348 cases

Gonorrhoea: 90

Syphilis: 8