Issue 11 / 30 March 2015

AUSTRALIAN women are being falsely diagnosed with gonorrhoea on the basis of unnecessary tests, often performed without their consent or their GP’s request, research suggests.

A study published online today by the MJA raises concern that pathology laboratories are now mostly using a dual nucleic acid amplification test (NAAT) for chlamydia and gonorrhoea rather than a single chlamydia detection test, even when GPs have only requested chlamydia testing. (1)

This is despite warnings from the manufacturers that NAAT testing has a low positive predictive value for gonorrhoea in low-prevalence settings such as the general community.

The study authors said there was likely to have been a “substantial number of false-positive results and unnecessary treatment” for gonorrhoea as a result.

Their study looked at gonorrhoea notifications for Victoria between 2008 and 2013 and gonorrhoea culture test results at the Melbourne Sexual Health Centre (MSHC) over the same period.

According to Medicare data testing with dual NAAT in Victoria rose 2.3-fold over the 6 years, with the proportion of positive tests remaining stable. The number of cases identified through NAAT (without culture) climbed from 98 in 2008 to 343 in 2013.

In the same period there was no observable increase in the proportion of women diagnosed by culture at the MSHC “Taken collectively, these data suggest that the prevalence of gonorrhoea among women remains very low and stable in Victoria (0.2%‒0.3%) and at the MSHC (0.4%‒0.6%), and that the rise in notifications is likely due to false-positive results”, the authors wrote.

The study also considered the cases of 25 women referred to the centre for culture testing after receiving a positive NAAT result for gonorrhoea. Only 10 of these women had a positive culture result (and of these nine presented with symptoms), with the authors suggesting that the remaining 60% could be false-positive results.

They concluded that positive NAAT results among low-risk women should be “regarded as doubtful” and followed up with confirmatory cultures.

“Currently, we are likely testing too many low-risk women, who are presumably attending a GP for chlamydia screening”, the authors wrote. They suggested that laboratories should suppress gonorrhoea results for women who were not at increased risk of the disease.

However, Dr Raymond Chan, speaking for the Royal College of Pathologists of Australasia, said suppressing positive results would be problematic.

“Some of these positive results are going to be true and we don’t know which ones”, he said.

The issue had generated much discussion among sexual health experts and microbiologists, Dr Chan told MJA InSight. He said many laboratories now routinely tested two targets before reporting a positive gonorrhoea result.

“If I was a GP and got a positive result back, I would phone the laboratory and ask if they had confirmed the result using a second target”, he said. “That doesn’t absolutely rule out the risk of a false-positive in a really low prevalence population, but it makes it less likely.”

Dr Chan also suggested it would be wrong to attribute most of the rise in gonorrhoea notifications among women over the past decade to false-positive results.

He said the 38 cases in the study identified by NAAT in 2008, rising to 86 cases in 2013, that were confirmed by culture, showed “clearly there has been a rise, although not nearly to the extent that NAAT testing alone suggests”.

Professor Basil Donovan, head of the sexual health program at the Kirby Institute at the University of NSW, told MJA InSight laboratories should suppress the NAAT gonorrhoea test result until the result of a confirmatory test on a second target was known but agreed that even then occasional false-positive results would still occur.

“Fortunately, for any individual GP this will be a rare event, and a third NAAT test or culture may help to sort out discrepant results.”

Professor Donovan said some increase in false-positive results was inevitable, with the increase in gonorrhoea testing.

However, he downplayed the authors’ suggestion that the finding that only 10 of 25 women attending MSHC with a positive NAAT had a positive culture result represented a false-positive rate of 60%.

“Some of those women might have spontaneously cleared their infection or may have taken antibiotics in the meantime that resulted in a negative culture”, he said, noting it was only a small number of cases.

The authors of an accompanying editorial in the MJA drew attention to the psychological impacts of false-positive test results, including anxiety and depression, feelings of guilt and self-blame, loss of self-esteem and self-confidence, feelings of social isolation and existential concerns. (2)

“Diagnosis of a sexually transmitted infection can also affect long-term sexual relationships, leading to concerns about trust and fidelity, and fear about disclosing results to a partner”, they wrote.


1. MJA 2015; Online 30 March
2. MJA 2015; Online 30 March

(Photo: wavebreakmedia / shutterstock)

4 thoughts on ““Unnecessary” gonorrhoea tests

  1. Department of Health Victoria Clinicians Health Channel says:

    I agree with Dr Chan and Prof Donovan that most labs (including ours) now do a second NAAT test for gonococcus before reporting a positive which reduces the false positive rates significantly. All outcomes of NOT reporting a confirmed positive test (even if th GP has not requested it) have not ben discussed. Lots of women can have asymptomatic infection which can be an issue in long term – infertlity, PID, other disseminated infecions, infections of new born babies etc. As suggested the GP needs to first confirm that the test has been confirmed by a second NAAT test (some labs include this on their report) and then counsel the patient appropriately. Suppressing a confirmed positive result (and not treating) is not ethical and certainly not good medical practice.

  2. Kirsten Small says:

    Performing an investigation without informed consent isn’t ethical either. If the lab can’t do a single test for only chlamydia they should contact the referring doctor before testing so they can get consent for the additional testing. Then you remove the tricky issue of what to do with a positive result for a test no one asked to be done.

  3. Department of Health Victoria Clinicians Health Channel says:

    Our understanding is that informed consent is already obtained for “STIs”. Most labs do contact the requesting doctor and  almost always the doctor has been happy to get the additional result. We think incidence of gonococcal disease is increasing in general and testing for it should always be coupled with Chlamydia testing. This will be the only way to know the true prevelance. It is a requirement for a NATA/RCPA accredited lab to do a confirmatory second Ng NAAT test.   

  4. Dr Sarah Garner says:

    The Medical Microbiologists of Victoria (MMV) group of the Royal College of Pathologists Australasia (RCPA) has major issues with this misleading paper and subsequent commentary in MJA Insight and ProMed. 

    In order to claim a government rebate for pathology testing, Australian diagnostic microbiology labs must have National Association of Testing Laboratories Australia (NATA)/RCPA accreditation, comply with all relevant Australian testing guidelines and be enrolled in appropriate Quality Assurance Programs (QAPs). This requires confirming any positive Neisseria gonorrhoeae NAAT result with culture or a second Nucleic Acid Amplification Test (NAAT) directed at a different genetic target.

    The paper has used no direct clinical evidence, but has come to its conclusions by combining data from three separate reporting sources. MSHC did not have access to routine Neisseria gonorrhoeae NAAT until after the study period and was not able to directly compare culture and PCR on a non-selected low risk female population. We believe that by using flawed methodology and without input from the laboratories performing the testing, they have made several false assumptions.

    This is in the setting of a local gonorrhoea and syphilis epidemic in MSM – and we are also seeing increasing numbers of cases of locally-acquired syphilis in women.  A full rebuttal is to follow.

    Dr David Leslie, Dr Sarah Garner and Dr Harsha Sheorey on behalf of MMV / RCPA


Leave a Reply

Your email address will not be published.