Testing for Neisseria gonorrhoeae by nucleic acid amplification testing of chlamydia samples using Roche Cobas Amplicor in a rural area in the north of England does not find more gonorrhoea in primary care

Men with urethral gonorrhoea are usually symptomatic, women are less likely to have symptoms.^1,2 If women are tested only for chlamydia and found to be negative, and tests for Neisseria gonorrhoeae are not performed, they are at risk of continuing infection with N gonorrhoeae as the infections may occur together.³ Patients concerned that they may have a sexually transmitted infection may access care through their general practitioner (GP). When testing both symptomatic and asymptomatic patients for chlamydia, GPs do not always test for N gonorrhoeae (local laboratory data). Even if they did, problems with sample transport, storage, etc, may influence sensitivity of cultures.^4,5

To assess the effect of the introduction of nucleic acid amplification testing (NAAT) methods for N gonorrhoeae in a rural area with low gonorrhoea prevalence, all samples submitted for Chlamydia trachomatis NAAT in north Cumbria were also screened for N gonorrhoeae with the Roche Cobas Amplicor amplification and detection system, used according to the standard programme method. N gonorrhoeae was cultured and identified according to national HPA standard operating procedures.

From 471 genitourinary medicine (GUM) samples, 10/16 positive N gonorrhoeae NAATs were confirmed by culture; from 966 primary care samples 1/17 positive N gonorrhoeae NAATs was confirmed by culture. Confirmation was more likely in men. Six women with positive NAAT for N gonorrhoeae were treated by their GP before culture confirmation (none of their partners had evidence of infection) (table 1). One patient in GUM had clinical signs suggestive of N gonorrhoeae infection but negative cultures. Even if all cases where GPs had given treatment had gonorrhoea, the confirmed positive rate would only be 50%.

Of those with a positive N gonorrhoeae NAAT, only two confirmed cases were asymptomatic (both female and identified through GUM where culture for N gonorrhoeae is routine practice) (table 1). The concern of the authors that had prompted this research was that asymptomatic women with N gonorrhoeae who attended their GP for care might, if only tested for chlamydia, continue with untreated N gonorrhoeae infection.

Although the study protocol included patient information explaining that false positive test results were possible, considerable anxiety was provoked in both patients and their GPs when a possible diagnosis of gonorrhoea was made. Our predictions from local GUM prevalence of gonorrhoea and the estimated sensitivity and specificity of the testing method suggested that unconfirmed positive samples from men were unlikely, but predicted approximately five unconfirmed positive results from women (one from GUM, four from primary care). We had four unconfirmed positive results from women in GUM and 16 in primary care. Cross reactivity may occur with some non-pathogenic strains of Neisseria and Lactobacillus species and may explain the higher positivity rate in women.⁶

Medical practitioners have differing responsibilities according to their area of work. GPs have a particular duty of care towards the individual. GUM physicians have a duty of care to the individual but also have public health responsibilities. Public health policies needed to protect the community may be in conflict with current bioethical principles regarding the care of individual patients.⁷

The additional laboratory costs of the N gonorrhoeae NAAT testing materials for this number of samples was approximately £1500, without taking into account the costs of laboratory or clinician time. We think that screening for N gonorrhoeae by NAAT with this method is neither cost effective nor appropriate in this low prevalence population.