Chlamydia retesting remains low among young women in Australia: an observational study using sentinel surveillance data, 2018–2022

Introduction

In Australia, chlamydia is the most frequently notified sexually transmissible infection (STI) with 86 916 notifications occurring in 2021.¹ Around two-thirds of notifications (n = 60 563) occurred among people aged 15–29 years, and half (n = 44 547) among women.¹ As over 85% of chlamydia infections are asymptomatic,² many people are unaware of their infection, which may persist for over a year.³ Chlamydia infections in people with female reproductive organs (from here on, the term women will be used) can lead to complications in the form of pelvic inflammatory disease (PID), chronic pelvic pain, ectopic pregnancy and infertility.⁴ Repeat infections are common with data from Australian primary care estimating a cumulative risk of re-infection of 20.3% among women aged 15–25 years within 5 months following treatment.⁵ Furthermore, each repeat infection increases the risk of PID by 20%.⁶ Past analyses of Australian sentinel surveillance data have shown low retesting and high re-infection rates following chlamydia infection. In mainstream primary care clinics (general practice) during 2008–2009, 24.6% of 16–29–year–olds were retested within 1.5–4 months (19% tested positive)⁷ and in specialist sexual health clinics during 2004–2008, 17.8% of heterosexual women were retested within 1–4 months (16.1% tested positive).⁸ Another study found 20.6% of women aged 15–29 years with chlamydia in 2016 were retested within 1.4–6 months.⁹

Increasingly, there has been a shift towards an enhanced case management approach to chlamydia that focuses on retesting and partner management, in light of evidence that widespread opportunistic screening is unlikely to reduce chlamydia prevalence.^10,11 An important component of this approach involves retesting women at 3 months following a positive test to detect re-infection, as recommended in Australian STI testing guidelines.¹² Repeat testing at 3 months allows for earlier treatment if a repeat infection is detected and an opportunity to reduce the likelihood of reproductive complications.¹³

In this retrospective cohort study, we sought to provide updated patterns in chlamydia retesting and repeat positivity for young women in Australia, with a particular focus on timely retesting (defined as within 2–4 months) as recommended by Australian STI guidelines.¹² Findings are intended to evaluate current chlamydia retesting patterns in Australia and to strengthen the case for action to increase retesting rates within 2–4 months as part of a multi–pronged approach to reduce the burden of chlamydia in Australia.

Materials and methods

Data collection and management

Deidentified routine clinical and testing data were retrospectively extracted from patient management systems at participating ACCESS sites using GRHANITE data extraction software. Data included in this study were obtained for the calendar years 2018–2022 from ACCESS site types including sexual health clinics, general practices who provide care to the general community, general practices who specialise in the care of gay and bisexual men (GBM) and community health clinics. Data items included age group, sexuality (including whether a women was ever flagged as bisexual, homosexual or heterosexual within the ACCESS dataset), sex and gender (including whether a women was ever flagged as transgender or other sex within the ACCESS dataset), ACCESS site type, having ever identified as a sex worker, patient location (metropolitan or non-metropolitan, where non-metropolitan included regional, rural and remote areas) based on their most recent postcode of residence using the Australian Statistical Geography Standard remoteness area classification, and patient country of birth, categorised as Australia or overseas. Data collected within ACCESS are what is routinely available within the electronic medical record system of participating clinics, thus completeness of some data items varied between types of clinical settings.

Data were included for women aged between 16 and 29 years who had at least one positive chlamydia test from any anatomical site (genitourinary, rectal or oral) during the period from 1 January 2018 to 30 November 2022, with a woman’s first positive test in the study period representing the starting point of follow up for that woman. A second test in the data set was defined as the next chlamydia test taken from any anatomical site that occurred immediately subsequent to a baseline positive test and before 31 December 2022, with no other chlamydia tests performed in between. The primary outcome was to determine retesting that occurred on time in accordance with Australian testing guidelines, which recommend retesting at 3 months¹² and to evaluate what factors increase or decrease the probability of retesting on time. In order to provide leeway for retesting to occur, a range of 2–4 months of a first positive chlamydia test was selected for our primary outcome and women with a first positive test up until 31 August 2022 were followed up. We also calculated repeat positivity for women retested on time. Sub-analyses investigated the following secondary outcomes: (1) retesting that occurred too early (from 7 days to 1 month of a positive chlamydia test) as tests performed this early are at increased risk of a false-positive result from persistent chlamydia DNA (even if performed as a test of cure in pregnant people and those with an anorectal infection treated with azithromycin¹²), for which women with a first positive test up until 30 November 2022 were followed up until 31 December 2022; and (2) to determine the distribution of retest occurrence in the 12 months following a positive chlamydia test, for which women with a first positive test until 31 December 2021 were followed up until 31 December 2022. Within ACCESS, tests that occur within 7 days are collapsed into one test event, so a positive test represents a 7-day window. A schematic of timelines for the analyses is shown in Fig. 1.

Fig. 1.

Timeline of cut-off dates by which a woman’s first positive test needed to occur for sub-analyses. (a) Women who had a second test performed within 1 month, (b) women who had a second test performed within 2–4 months, (c) women who had a second test performed within 12 months, and (d) total study period.

Results

Overall, 9253 women aged 16–29 years had at least one positive chlamydia test within the study period from 1 January 2018 to 31 December 2022. Among the 9253 women within the total study period, 162 (1.8%) and 16 (0.2%) were ever flagged as transgender or other sex, respectively. Among the same 9253 women, 899 (9.7%) were ever flagged as bisexual only; 65 (0.7%) as homosexual only; 6500 (70.2%) as heterosexual only; with the remainder a combination of the three sexuality variables and no missing data. The number of ACCESS clinics and chlamydia tests contributed by ACCESS site type for the entire study period is in Table 1.

Among 8758 women who had their first positive test before 31 August 2022 and contributed to the analysis of our primary outcome of retesting within 2–4 months, most were aged 20–24 years (n = 4453, 50.8%), resided in metropolitan areas (n = 6050, 69.1%) and attended a sexual health clinic for testing (n = 7226, 82.5%). A total of 849 participants (9.7%) identified as having ever worked as a sex worker. Table 2 provides a breakdown of the proportions retested and retesting positive within 2–4 months and within 1 month by year and demographic characteristics. For our secondary outcomes of retesting within 1 month and within 12 months of their first positive test, population demographics for these women were very similar to those who had a retest within 2–4 months (Table 2). A schematic of timelines for the analyses is shown in Fig. 1 and a flowchart describing the number of women retested by study outcome in shown in Fig. S1.

Distribution of second tests within 12 months

Overall, among those who had their first positive chlamydia test between 1 January 2018 and 31 December 2021, the median time to retest was 86.0 days (IQR 46.0–140.8 days) with 69% of retests occurring within 4 months (Fig. 2).

Fig. 2.

Histogram showing the distribution of retest occurrence within 12 months of a woman’s first positive chlamydia test that occurred between 1 January 2018 and 31 December 2021. Dotted vertical lines indicate 2 months and 4 months.

Among the 4228 women who had their first positive test before 31 December 2021 and their second test within the remaining study period, only 96 (2.3%) had their second test at a discordant ACCESS site type e.g. first test at a sexual health clinic and second test at a general practice.

Discussion

Among women attending STI and BBV sentinel surveillance sites in Australia with at least one positive chlamydia test between January 2018 to August 2022, we observed that only 16.2% had a repeat test within 2–4 months, as recommended in Australian STI testing guidelines. Among women retested within 2–4 months, 12.6% tested positive. Retesting on time was lower during COVID-19 pandemic years (2020–2022) compared to non-COVID-19 years. Few women were retested too early but 20.4% of those retested within a month tested positive. In the 12 months after a positive chlamydia test, most repeat tests occurred within the first 4 months. These findings reinforce current testing guidelines that recommend that patients with a positive chlamydia test be retested at 3 months to identify a persistent or new infection (re-infection), to initiate repeat treatment and reduce the likelihood of reproductive complications.

Our finding of 16.2% of women retested and 12.6% with a repeat positive test within 2–4 months is slightly lower than previously reported in Australia,^7–9 even prior to the onset of the COVID-19 pandemic. The lower retesting rates observed in this study may be due to the ACCESS system now having a larger number and different composition of clinical sites compared to when it commenced. For example, the early ACCESS system included family planning clinics, that may be more likely to retest patients. Additionally, concerted efforts to increase chlamydia testing as part of an overall chlamydia response, including a multifaceted chlamydia testing intervention were underway in Australia between 2010 and 2015.¹¹ It is also possible that some patients who tested positive during a COVID-19 pandemic year, were advised to delay their retest due to community lockdowns and may contribute to lower retesting during this period. In our univariable analysis, we also found that retesting within 2–4 months was more likely for women who identified as a sex worker or resided in non-metropolitan areas. Higher retesting rates among women who had ever identified as a sex worker is likely influenced by mandatory STI testing regulations in various state and territories.¹⁵ Of note, there is no evidence that sex workers in Australia have higher STI rates compared to the general population, with the Australian sex industry adopting safer sex practices through advocacy, peer-based education and support and outreach services.¹⁶ Although guidelines recommend regular STI and BBV testing, sex workers may request more frequent testing to comply with workplace and other local legal frameworks.¹⁶ The repeal of mandatory requirements to undergo regular 3-monthly STI testing in Victoria as of May 2022 is likely to alter this outcome in future years.¹⁷ The higher odds of retesting for women residing in non-metropolitan areas may reflect a combination of higher GP chlamydia testing rates in non-metropolitan areas¹⁸ and people residing in regional or rural areas being more likely to attend the same clinic or a clinic in the same area.¹⁹ Importantly, a higher proportion of positive retests occurred within 1 month of an initial positive test compared to those retested within 2–4 months. This may represent false-positive tests due to persistent chlamydia DNA and are likely being performed too early. Additionally, given that most chlamydia tests in this analysis were performed at sexual health clinics, it is possible that women are being referred back to their primary care physician for retesting, and thus contributing to low overall retesting rates. This may be acting as an additional barrier and represent a missed opportunity for retesting to occur. Further exploration into the feasibility of sexual health clinics playing a greater role in chlamydia retesting is required.

In addition to providing an update to chlamydia retesting figures in Australia, the strengths of this study include the assessment of multiple site types from around Australia including sexual health clinics, general practices and community health clinics, along with offering insights into individual-level factors associated with retesting in accordance with Australian guidelines; a comparison of retesting both before and during the COVID-19 pandemic; and a particular focus on women, who are disproportionately burdened by the reproductive complications associated with chlamydia infections. However, there are important considerations to note when interpreting our findings. First, being a sentinel surveillance system, sites represented in this analysis see a larger proportion of people at greater risk of STIs, reflected by sexual health clinics contributing more than 80% of our testing data. Second, women may have been retested at another site not participating in ACCESS or, for travellers, returned to their home country before retesting could occur, and therefore not had their retest observed in our data. This would result in an underestimation of the true rate of retesting. Third, as test events that occur within 7 days are collapsed into one event within ACCESS, if a woman had a second test within 7 days of their first positive test and did not have another chlamydia test for the remaining study period, their second test would not have been captured. This would result in an overestimation of the number of women who did not receive a second test in the study period, when in fact they did receive a second test it just occurred too early. Fourth, caution should be exercised when attributing a person’s second positive test as a true re-infection. Given that guidelines do not recommend a test of cure, except for pregnant people and anorectal infection treated with azithromycin,¹² it is difficult to differentiate re-infection from a persistent primary infection. Fifth, as there was a large number of incomplete data for some demographic variables such as sex worker status, patient location and country of birth, these factors were not included in multivariable logistic regression analyses. Finally, generalisability of the findings should be limited to countries and regions with similar access to primary care and testing services as Australia.

As part of a suite of interventions to reduce the morbidity from chlamydia, increasing retesting within 2–4 months following a positive test can have significant individual and population level benefits by reducing the risk of reproductive complications and onward transmission. An Australian modelling study has estimated a reduction in the prevalence of chlamydia from 4.6% to 2.6% over 4 years when, in addition to increasing testing coverage, the proportion retested within 4 months of treatment is doubled from the rate achieved in a large cluster–randomised controlled trial among heterosexual 16–29-year-olds in Australia.²⁰ Additional modelling estimated that 22% of all-cause PID could be prevented by annual chlamydia testing intervals.²¹ Combined with the knowledge that each repeat chlamydia infection increases the risk of PID by 20%,⁶ the importance of prompt retesting in a population already at a higher risk of re-infection cannot be understated. Interventions aiming to increase chlamydia retesting, including patient text message reminders and postal home collection kits, have been shown to increase retesting rates within 1–4 months of a chlamydia diagnosis.^22,23 Studies such as the Management of Chlamydia Cases in Australia trial²⁴ are underway to ascertain how best to implement such strategies within the complex and competing priorities of the primary care environment, where many STIs are diagnosed and managed.¹⁹ In addition to increasing retesting, a greater understanding of what women perceive as the risks and consequences of re-infection is required, as part of a multipronged approach to reducing the health impacts from chlamydia acquisition.

Our findings have demonstrated that chlamydia retesting within 2–4 months among young women, as recommended in Australian STI testing guidelines, continues to be low, with repeat infections common. These findings reinforce the importance of adhering to current testing guidelines to promptly detect re-infection and commence treatment. In the context of an increasing paradigm shift towards an enhanced case management approach to reduce reproductive complications from chlamydia,^25,26 improved retesting is one way in which we can work towards reducing the burden of chlamydia in Australia.

Supplementary material

Supplementary material is available online.