Introduction To date, there is limited data on Neisseria gonorrhoeae (NG) bacterial load in relation to transmission and symptoms of NG infection. Also, extra-genital sites are not often tested apart from specific risk groups. This could lead to untreated infections that potentially facilitate transmission of NG. In this study we describe the NG bacterial load in relation to sample site, sexual orientation, and age.

Methods Routine diagnostics samples of the STI clinic of the South Limburg Public Health Service between 2012 and May 2016 were used. In this period, 1141 samples (883 male and 258 female) from 836 patients were NG positive, among which 237 urine samples, 130 genital swabs, 394 anorectal swabs, and 380 oropharyngeal swabs. Bacterial load was determined by interpolation of a standard curve using the COBAS 4800. Multiple linear regression was used to describe bacterial load in which sample site, sexual orientation, and age were the determinants.

Results In 471 of 629 (74.9%) patients with an extra-genital NG positive sample, only the extra-genital sample was positive, among these were 367 men who have sex (MSM) with men, 34 heterosexual men (HSM), and 70 women. Most patients were positive at a single sample site, 221 oropharyngeal (130 MSM, 32 HSM, and 59 women) and 165 anorectal respectively (154 MSM, 2 HSM, and 9 women). Sample site and age were significant determinants for load (both p<0.001), in contrast to sexual orientation (p=0.096). When comparing sample sites oropharyngeal swabs have a significant lower load (p<0.001), whereas urine samples have a significant higher load (p<0.001).Genital and anorectal swabs loads do not differ (p=0.315). Lower bacterial load appears to be correlated with older patients.

Conclusion NG bacterial load is for a large part driven by sample site. Oropharyngeal NG infections are often asymptomatic which could be related to a lower bacterial load. However, the role of the observed load differences in transmission and symptoms should be addressed in future studies.