Bacterial sexually transmitted infections (STI) have an important impact on reproductive health worldwide. In Europe, STI risk behaviour and incidence rates are on the rise among young population. Neisseria gonorrhoeae outbreak in very young adolescents has been reported in Catalonia and other STI on the rise.1

Chlamydia trachomatis is the most common STI worldwide, with estimated 105.7 million cases in adults aged 15 and 49.2 In Europe is the most frequently reported with a notification rate of 182 per 100,000 habitants in 2013, 67% of which were reported in young adults <25 years. Gonorrhoea was more frequent in men than in women, predominantly in men who have sex with men (MSM) and 39% being reported among young adults.3 As for the Catalan region, C. trachomatis prevalence has been on the rise among young adults <25 years of age showing a prevalence of 5.8% in 2007 and 8.5% in 2012.4

Most C. trachomatis infection is asymptomatic leading to undiagnosed infection and increased risk of complications. Consequently, although screening programs for C. trachomatis detection are important in order to reduce the C. cases, these can be very expensive.5,6 To reduce costs, previous studies have shown that specimen pooling is beneficial for high-throughput testing in low-prevalence populations (≤10%) using non-invasive specimens such as first void urine by nucleic acid amplification tests (NAATs).7

There are currently no commercially available NAATs approved by the Food and Drug Administration for use with pooled specimens. However, several studies have shown an excellent correlation between the results of pooled specimens and individually tested specimens for C. trachomatis detection.8–12

The aims of this study were (i) to describe the performance characteristics of a PCR 7-STI detection assay using pooled urine specimens for C. trachomatis, N. gonorrhoeae and M. genitalium infections; (ii) to estimate the cost saving of a pooling strategy and (iii) to describe the prevalence, risk factors and co-infections of C. trachomatis, N. gonorrhoeae and M. genitalium among young under 25 years in Catalonia.

Since 2007, in Catalonia, C. trachomatis prevalence monitoring with bio-behavioural data was carry out in the sentinel population of young people as a part of the integrated epidemiological surveillance system. The objectives of these periodic studies are to know and monitor C. trachomatis prevalence and risk factors of infection among those under 25 years of age attended in sexual and reproductive health centres (ASSIR) and youth care centres.

The study design selected was a cross-sectional observational study of C. trachomatis, N. gonorrhoeae and M. genitalium among young attending 24 ASSIR and 3 youth care centres in Catalonia. These centres are characterized by offering a service of family planning, specific attention to young people, maternal-child care, prevention, diagnosis of gynaecological diseases. Women served mostly in these centres.

The inclusion criteria were sexually active ≤12 months and aged between 16 and 25 years attending at ASSIR and youth care centres for any reason such as general gynaecological attention, STI/HIV screening, symptoms, contraception methods, etc. The recruitment period will be during the first semester of 2016. Epidemiological data was collected using a standardized questionnaire, including socio-demographic and behavioural variables as described by López-Corbeto et al.4 Data anonymity was assured, as no personal identifiers were included in the database. This study was approved by the local Research Ethics Committee: CEICPI-17-217.

The present study, introduces for the first time in Catalonia a cost saving strategy for the STI prevalence and epidemiological monitoring of young population through the introduction of pooled urine specimens using NAAT's technology. The STI pooling strategy had been used in diverse scenarios as for opportunistic testing of C. trachomatis within a US Infertility Prevention Project including multiple STI measures using hierarchical pooling16 or for triple-site pooling among MSM17 or within asymptomatic pregnant women.18

Our findings showed savings cost of 33% as similar found by Peeling et al.9 when considering an initial 7% C. trachomatis prevalence at pool size of 3 specimens. Different costs reductions were found according to the pool size used to a specific prevalence. Shipitsyna et al. stated that cost-benefit depend on the prevalence of infection in the population and pooling size chosen.12 Peeling et al., compared cost savings using different pool sizes (2–5 specimens) at 5%, 10% and 20% C. trachomatis prevalence, obtaining savings of 31–39% (2–5 specimens/pool) at 10% prevalence and as high as 40–57% (2–5 specimens/pool) at 5% prevalence.9 Other study by Kucinskiene et al.19 obtained 7.1% C. trachomatis prevalence for the age group of 20–24 using three samples per pool and overall cost saving of 85%.

These results bring the need to perform further analysis increasing the number in each pool in order to evaluate a further increase in cost-savings within this population.

Our cost saving findings are consistent with other studies7,9,12,18 in a reduction between 30% and 50%. We analyzed saving costs based only in reagent costs and savings were calculated based on the percentage reduction in the number of tests associated with the pool strategy. The estimation of the full costs of the tests was not assessed because, tests kits cost and personnel cost varies according to the laboratory. In this way, the savings obtained have a wider applicability and comparability. This strategy has also been used by other authors.9 However, when cost of reagent, consumables and personnel were included into analysis, get a range of savings in reagents costs between 39% and 43%.20 The pooling strategy carried out in our context is a cost-saving strategy for epidemiological studies and screening programs as supported by Morré et al.21

The STI prevalence rates among the young population in our study are low except to C. trachomatis that continues on the rise. C. trachomatis prevalence was higher than the median prevalence observed in previous studies in Catalonia4 and by Fernández-Benítez et al. in Spain.22 In Catalonia the 10-year evolution of C. trachomatis showed a median prevalence of 7.7% and continues on the rise among young adults <25 years. The low prevalence obtained for N. gonorrhoeae was similar to those found in previous studies in our setting.4

For the first time, prevalence data of M. genitalium in Catalonia are showed. This prevalence is low in our study. In Europe prevalence range between 3% and 10%.23,24 In France, Pereyre et al.24 found comparable figures than ours within a similar population between 16 and 24 years (3.6%). On the contrary, in the USA the prevalence is higher. Getman et al.23 found 20.4% prevalence among young <30 years. Both studies shared similar settings and population. The only studied carried out in Spain by Asenjo et al.25 found prevalence of 3.3%, but in a symptomatic general population.

It has to be careful that with the prevalence rate found and the extensive testing, detection and subsequent antimicrobial treatment of M. genitalium performed in some settings may result in the selection of antimicrobial resistance punches, so there is a consensus of M. genitalium test in patients with non gonocal urethrithis, pelvic inflammatory disease or persistent vaginal discharge, so selective screening for M. genitalium in the general population may be a possibility in the future.26,27

Determinants associated with STI detected are similar than observed in previous studies.4,28 Use PECP appears for the first time as a C. trachomatis determinant in our studies. There is a concern that women who have easy access to a postcoital form of contraception may in fact have more unprotected intercourse and abandon more effective forms of regular contraception. Studies have also shown about the impact of increased access to PECP on sexual risk taking behaviours and STI29,30,31 and suggest that females who use PECP do not necessarily consider using a condom for STI prevention. In a large Canadian study, only 27% of current PECP users reported concurrent use of condoms.32

Our data are consistent from those reported previously23 in that testing for C. trachomatis and other sexually transmitted microorganisms using sensitive NAAT methods revealed that the majority of samples were infected with a single microorganism. This apparent predominance of subjects harbouring single-organism infections has implications for the diagnosis and treatment of individuals who are at high risk for STIs. Current treatment guidelines recommend antibiotic therapy that is specific to each microorganism33 and, since coinfection with one or more STI may be uncommon, the choice of therapy for managing mucosal epithelial inflammatory conditions should be guided by the employment of clinically validated diagnostic methods, rather than a syndromic management approach.

The limitations showed in our study are: (i) STI prevalence could be a slight underestimation given the pool strategy used because the effect of dilution could give a loss of sensitivity.9 (ii) Urine sample is probably not the most ideal sample in women and can give up to 10% of false negatives,34 but according to previous studies, non-invasive detection options, such as urine sample, could eliminate some of the barriers for the STI detection. Patients clearly prefer non-invasive methods and could substantially increase the acceptability and convenience of screening in a variety of settings. The easy collection and transport of urine samples makes the large-scale analysis of the selected populations feasible, especially considering that, in our context, young population is being analyzed and part of the study, which is carried out in non-health environment as youth care centres. In addition, current PCR techniques have high sensitivities and specificities in urine samples.9,35 (iii) The study sample was representative of the participating centres so the number of men is scarce but previous studies do not differ in C. trachomatis or M. genitalium prevalence according to sex.36,24 Regarding pregnancy, it is considered relevant to study this population more thoroughly, given that STI prevalence data in pregnant women in Spain is scarce, only Piñeiro et al.37 has carried out an analysis of these characteristics.

Despite these limitations, the present study introduces for the first time in Catalonia a cost saving strategy for STI prevalence and epidemiological monitoring of young population through the introduction of pooled urine specimens and it shows that the pooling carried out in our context is a cost-saving strategy for epidemiological studies and it can impact in the feasibility of STI screening programs. In the same way this study presents STI prevalence in young population, emphasizing that C. trachomatis prevalence continues to increase among this population and for the first time in Catalonia, are shown prevalence data of M. genitalium among young.

The authors have no conflicts of interest to declare.