Abstract
Abstract
Objectives
Canadian guidelines recommend HIV testing for individuals being evaluated for syphilis. Our objective was to examine three aspects of HIV testing (ie, if an HIV test occurred, the timing of the HIV test in relation to the syphilis test and the proportion with a positive HIV test result) among syphilis tests between 2017 and 2022 from individuals with no evidence of a previous HIV diagnosis.
Design and setting
This study is a retrospective analysis of comprehensive laboratory testing data from Ontario’s provincial public health laboratory.
Participants
Direct fluorescent antibody (DFA) and serological non-prenatal syphilis tests were conducted from 1 January 2017 to 31 December 2022, from individuals aged ≥15 years with no evidence of a previous HIV diagnosis (n=3 001 058 total tests). Positive syphilis tests were categorised using the rapid plasma reagin (RPR) titre as ‘current’ (DFA+/RPR≥1:8) or ‘historical’ (RPR<1:8). Exposure categories were assigned using individually linked HIV exposure category data retrieved from the laboratory’s HIV DataMart.
Primary and secondary outcome measures
The number and proportion of syphilis tests with a corresponding HIV test on the same day or within 7, 28, 90 or 180 days, and, among those with an HIV test within 28 days, the number and proportion with an HIV-positive test result.
Results
From 2017 to 2022, 1 516 726 and 1 484 332 syphilis tests among males and females, respectively, were included in the analysis. Individuals with a positive syphilis result were less likely to be tested for HIV within 28 days of their syphilis test compared with those with a negative syphilis test result (74.7% vs 91.1% in males, 97.5% CI (−0.17 to −0.16); 65.2% vs 92.4% in females, 97.5% CI (−0.28 to −0.26)). Males with ‘current’ positive syphilis test results were less likely than males with ‘historical’ positive syphilis results to be tested for HIV within 28 days (69.1% vs 76.6%, 97.5% CI (−0.084 to −0.066)); this was not true in females (67.1% vs 64.4%, 97.5% CI (0.0062 to 0.049)). Males overall and males with ‘current’ syphilis were more likely to be diagnosed as HIV-positive (p<0.025).
Conclusions
Most individuals who tested for syphilis at Public Health Ontario were also tested for HIV; however, those who tested positive for syphilis were less likely to be tested, representing an opportunity for enhanced HIV testing. Ensuring that individuals with syphilis are tested for HIV may help identify previously undiagnosed individuals living with HIV.
Keywords: HIV & AIDS, Syphilis, Sexually Transmitted Disease, Diagnostic microbiology, Public health
STRENGTHS AND LIMITATIONS OF THIS STUDY.
As the provincial public health laboratory conducts nearly all syphilis and HIV diagnostic and HIV viral load testing in the province, our data represents a comprehensive analysis of our research questions, and our results are representative of the province.
Due to incomplete or inconsistent data and anonymous HIV testing, an individual’s HIV tests may not always link to their syphilis tests, which can affect the identification of people previously diagnosed with HIV (and exclusion of their syphilis tests) and the ability to identify corresponding HIV tests.
As we were limited to syphilis laboratory data alone and did not employ longitudinal analyses, we could not conclusively distinguish between current and treated/resolved syphilis infections (potential for misclassification); however, while not validated, our definition of ‘current’ syphilis infections (rapid plasma reagin≥1:8) reflects a conservative, guideline-based estimate informed by expert consultation that, at the population level, suffices in addressing our questions.
We had incomplete data with respect to the HIV exposure category, and these data are subject to recall and social desirability biases, which may affect interpretations among exposure categories.
Introduction
Despite decreases in HIV testing and diagnosis rates in 2020 and 2021 in Ontario, Canada, due to the COVID-19 pandemic, rates returned to near prepandemic levels in 2022.1 Consequently, along with other interventions, timely and prudent testing for HIV remains an important secondary prevention measure. Concurrent with the robust rates of HIV diagnoses, the rates of infectious syphilis have been rising, which, with the exception of 2020, have increased steadily and dramatically (>threefold) in Ontario between 2013 and 2022.2 This rise in syphilis cases, and increased syphilis screening and diagnostic testing associated with this rise, represents opportunities for the identification and testing of individuals at elevated HIV risk.
Guidelines from the Public Health Agency of Canada (PHAC) recommend screening for syphilis for individuals with new or multiple sex partners, or on request.3 The association between a bacterial sexually transmitted infection (STI) diagnosis and subsequent HIV acquisition is well documented.4 As such, PHAC guidelines recommend that individuals being evaluated or treated for syphilis be screened for HIV,5 whereas Ontario’s HIV testing guidelines recommend HIV testing for members of populations with higher HIV rates following an STI diagnosis.6 PHAC guidelines further recommend that individuals at risk for HIV be screened at least annually.7 The United States Centers for Disease Control and Prevention (CDC) similarly recommends that HIV testing be performed concurrently with testing for other STIs.8 Because of the high correlation between STIs, especially syphilis, and HIV acquisition, the CDC guidelines also state that if the initial HIV testing opportunity is missed, an STI diagnosis should be used as an opportunity to test for HIV.8 Given the epidemiology of HIV and syphilis and their respective testing guidelines, individuals testing for syphilis represent an informative population to investigate HIV testing efforts. HIV testing frequencies can also be compared with published guidelines to facilitate assessment of recommended HIV testing.
Variability exists in HIV risk following an STI diagnosis, with gay, bisexual and other men who have sex with men (GBMSM) at elevated risk. One study in New York City demonstrated that 1 in 20 GBMSM were diagnosed with HIV within a year of their syphilis diagnosis.9 In a Danish GBMSM cohort, a new syphilis diagnosis was associated with a 9.8% risk of acquiring HIV over the subsequent 5 years.10 In a cohort of men in Baltimore, while an STI diagnosis increased the risk for a subsequent HIV diagnosis in all men, GBMSM had a much higher HIV incidence than non-GBMSM.11 Less is known about the HIV acquisition risk in those who receive negative STI test results. Though HIV incidence and prevalence are broadly lower in women than men in Canada,12 13 the frequency of HIV screening in women who have been tested for syphilis is unknown. Surveillance data in Manitoba, Canada, recently demonstrated greater social vulnerability among newly HIV-diagnosed women compared with men, suggesting that at-risk women may be more difficult to reach with prevention efforts.14
In Ontario, testing for syphilis and HIV is performed almost exclusively at Public Health Ontario’s (PHO) laboratory, which is the provincial public health reference laboratory. It is unclear whether individuals in the province are being screened for both infectious diseases as per the aforementioned guidelines or whether gaps exist in screening practices, as has been demonstrated elsewhere.15 Using laboratory testing data, our objective was to examine three aspects of HIV testing among syphilis tests performed between 2017 and 2022 from individuals with no evidence of a previous HIV diagnosis: (1) to determine if an HIV test occurred; (2) the timing of the HIV test in relation to the syphilis test and (3) the proportion with a positive HIV test result. Our comprehensive dataset allows for the assessment of HIV testing practices over different time windows (eg, within 28–180 days following a syphilis diagnosis), which enables us to determine whether STI screening is occurring in Ontario as recommended. To the best of our knowledge, this is the first time this type of analysis has been done at the provincial level.
Methods
The vast majority of syphilis screening and all syphilis confirmatory testing in Ontario is centralised at PHO. Syphilis serology and direct fluorescent antibody (DFA) testing data were extracted from PHO’s laboratory information management system for tests from 1 January 2017 to 31 December 2022. The following syphilis tests were excluded: quality control tests; prenatal tests; tests from individuals aged <15 years (and unknown date of birth) and duplicate tests from the same individual on the same date.
HIV testing in Ontario is centralised at PHO except for rare exceptions. As a result, the HIV DataMart contains nearly all HIV diagnostic and viral load testing conducted in Ontario. HIV testing data (HIV serology and point-of-care test result, HIV exposure category and identifying information) were extracted from PHO’s 2022 HIV DataMart, from the date when data were first collected (1985 onwards for HIV diagnostic testing and 1996 onwards for HIV viral load testing) to 31 December 2022. Syphilis tests and HIV tests from the same individual were linked via matching health card numbers, or if missing, first name, last name and date of birth (exact match). Since the purpose of HIV screening is to find new HIV diagnoses, we restricted syphilis tests to individuals with no evidence of a previous HIV diagnosis as of the date of the syphilis test. To do this, we excluded (1) all syphilis tests from an individual who reported being previously diagnosed with HIV (via the HIV test requisition or a follow-up questionnaire sent to the ordering physician of HIV-positive tests); (2) all syphilis tests occurring after an individual’s first positive diagnostic HIV test and (3) all syphilis tests occurring on the same date or after an individual’s first HIV viral load test. For each syphilis test, the number of days between the date of the syphilis test and the most proximal-in-time HIV test (either preceding or following) was calculated. This was used to categorise syphilis tests with respect to the timing of the ‘corresponding’ HIV test (ie, same day (0 days), same day ±28 days, etc). Similarly, the number of days to the patient’s subsequent positive HIV test (if any) was calculated for each syphilis test (note that the number of days following a previous positive HIV test was not calculated, as these syphilis tests would have been excluded for already being HIV-diagnosed per above). The date the specimen was received/logged in the laboratory was used as the test date instead of the collection date because the latter is inconsistently provided. The analysis was completed on the test level, as opposed to the individual level, with individuals having multiple syphilis tests included in the analysis.
Given that we were limited to syphilis laboratory testing data alone (ie, no clinical information) and that an individual is likely always to screen positive for syphilis once infected, we aimed to provide a population-level approximation of current or active versus historical syphilis infections. We created two categories of positive syphilis tests (1) ‘current’: DFA-positive or a positive chemiluminescent microparticle immunoassay (CMIA) serology screen with a rapid plasma reagin (RPR) antibody titre of ≥1:8 was considered more likely to represent current syphilis infections and (2) ‘historical’: a positive CMIA screen with an RPR<1:8 was considered more likely to represent historical (treated/resolved) infections. All other syphilis tests were considered ‘non-positive’ tests (including negative, inconclusive and invalid results). Invalid results were retained, as they still represent instances of syphilis tests being ordered/requested.
HIV laboratory surveillance data includes the collection of HIV risk factors on the test requisition form and a follow-up questionnaire after diagnosis to create HIV exposure categories; Ontario’s syphilis testing data do not include this information.16 To assign exposure categories to syphilis tests, individually linked HIV exposure data were used. As this information is not reported for the majority (>70%) of HIV tests,17 HIV risk factors reported on earlier or later HIV tests (whichever was closest in time) were used to assign exposure categories for the syphilis tests that had corresponding HIV tests. In doing this, 65% of syphilis tests are assigned an exposure category reported within 90 days, 80% within a year and 87% within 2 years. These exposure categories are assigned through a hierarchy related to HIV risk in the following order: male-to-male sexual contact, heterosexual contact and ‘unknown HIV exposure’ (no HIV risk factor reported (missing data)).
Statistical tests of trends over time used logistic regression with year as the independent variable. Odds ratios (ORs) and 97.5% confidence intervals (CIs) are reported. When comparing two proportions, the 97.5% CI for the difference between the proportions is reported. The 97.5% confidence level was selected to account for the large surveillance population sizes. All analyses were completed in SAS Enterprise Guide V.8.4.
Patient and public involvement statement
The work completed in this study is considered routine public health practice and not research. As such, it was not appropriate or possible to involve patients or the public in the design, conduct, reporting or dissemination plans of our work.
Results
Between 2017 and 2022, a total of 1 516 726 syphilis tests among males and 1 484 332 syphilis tests among females were included in the analysis. The proportion of tests that were positive for syphilis increased from 3.2% in 2017 to 6.6% in 2022 among males (OR 1.16, 97.5% CI (1.14 to 1.18)) and from 0.5% in 2017 to 1.3% in 2022 among females (OR 1.21, 97.5% CI (1.15 to 1.27)). Among females, the proportion of positive tests that were categorised as ‘current’ infections increased from 19.0% in 2017 to 35.9% in 2022 (OR 1.22, 97.5% CI (1.17 to 1.28)), whereas this decreased among males from 28.9% to 23.3% (OR 0.96, 97.5% CI (0.93 to 1.00)). In 2020, the number of syphilis tests decreased by 27.9% among males and 24.6% among females before recovering and surpassing 2019 counts in 2022.
Non-positive syphilis tests
Between 2017 and 2022, the proportion of non-positive syphilis tests that had an HIV test on the same day ±28 days increased from 87.7% to 92.7% among males (OR 1.14, 97.5% CI (1.08 to 1.19)) and from 90.1% to 93.3% among females (OR 1.08, 97.5% CI (1.04 to 1.13), table 1). In 2022, 90.7% of males and 91.5% of females had an HIV test on the same day; 92.7% and 93.3% within ±28 days; 93.4% and 93.8% within ±90 days and 93.8% and 94.2% within ±180 days, respectively (table 2). Between 2017 and 2022, 4.2% of non-positive tests among males and 3.8% among females had no corresponding HIV test regardless of time window (3.8% and 3.5%, respectively, in 2022 alone).
Table 1. Number of syphilis tests and the number/proportion with a corresponding HIV test on the same day ±28 days, among males and females, Ontario, PHO, 2017–2022.
| Males | Females | |||
|---|---|---|---|---|
| Total syphilis tests, N | Number/proportion that had an HIV test on the same day ±28 days, n (%(n/N)) | Total syphilis tests, N | Number/proportion that had an HIV test on the same day ±28 days, n (%(n/N)) | |
| Non-positive syphilis tests | ||||
| 2017 | 223 749 | 196 244 (87.7) | 229 808 | 207 138 (90.1) |
| 2018 | 250 420 | 224 380 (89.6) | 256 726 | 236 174 (92.0) |
| 2019 | 267 712 | 243 082 (90.8) | 270 025 | 250 143 (92.6) |
| 2020 | 191 064 | 176 202 (92.2) | 203 238 | 188 933 (93.0) |
| 2021 | 249 529 | 232 527 (93.2) | 249 674 | 233 178 (93.4) |
| 2022 | 262 800 | 243 590 (92.7) | 262 899 | 245 327 (93.3) |
| 2017–2022 | 1 445 274 | 1 316 025 (91.1) | 1 472 370 | 1 360 893 (92.4) |
| All positive syphilis tests | ||||
| 2017 | 7313 | 4657 (63.7) | 1243 | 764 (61.5) |
| 2018 | 9236 | 6327 (68.5) | 1517 | 948 (62.5) |
| 2019 | 11 909 | 8780 (73.7) | 1726 | 1126 (65.2) |
| 2020 | 10 662 | 8184 (76.8) | 1599 | 1032 (64.5) |
| 2021 | 13 904 | 10 949 (78.7) | 2383 | 1574 (66.1) |
| 2022 | 18 428 | 14 492 (78.6) | 3494 | 2351 (67.3) |
| 2017–2022 | 71 452 | 53 389 (74.7) | 11 962 | 7795 (65.2) |
| ‘Current’ positive syphilis tests | ||||
| 2017 | 2113 | 1212 (57.4) | 236 | 131 (55.5) |
| 2018 | 2282 | 1470 (64.4) | 295 | 169 (57.3) |
| 2019 | 2905 | 1997 (68.7) | 406 | 249 (61.3) |
| 2020 | 2675 | 1919 (71.7) | 449 | 293 (65.3) |
| 2021 | 3388 | 2505 (73.9) | 831 | 603 (72.6) |
| 2022 | 4298 | 3099 (72.1) | 1256 | 886 (70.5) |
| 2017–2022 | 17 661 | 12 202 (69.1) | 3473 | 2331 (67.1) |
| ‘Historical’ positive syphilis tests | ||||
| 2017 | 5200 | 3445 (66.3) | 1007 | 633 (62.9) |
| 2018 | 6954 | 4857 (69.8) | 1222 | 779 (63.7) |
| 2019 | 9004 | 6783 (75.3) | 1320 | 877 (66.4) |
| 2020 | 7987 | 6265 (78.4) | 1150 | 739 (64.3) |
| 2021 | 10 516 | 8444 (80.3) | 1552 | 971 (62.6) |
| 2022 | 14 130 | 11 393 (80.6) | 2238 | 1465 (65.5) |
| 2017–2022 | 53 791 | 41 187 (76.6) | 8489 | 5464 (64.4) |
‘Current’ positive syphilis tests: DFA-positive or a positive CMIA serology screen with an RPR antibody titre of ≥1:8 were considered more likely to represent current (untreated) syphilis infections; ‘historical’ positive syphilis tests: positive CMIA screen with an RPR<1:8 were considered more likely to represent historical (treated/resolved) infections.
CMIA, chemiluminescent microparticle immunoassay; DFA, direct fluorescent antibody; PHO, Public Health Ontario; RPR, rapid plasma reagin.
Table 2. Number of syphilis tests (N) and the number/proportion with a corresponding HIV test on the same day, on the same day ±28 days, on the same day ±90 days and on the same day ±180 days (n), by syphilis test result and year, among males and females, Ontario, PHO, 2022.
| Total syphilis tests | Number/proportion that had an HIV test on the same day | Number/proportion that had an HIV test on the same day ±28 days | Number/proportion that had an HIV test on the same day ±90 days | Number/proportion that had an HIV test on the same day ±180 days | |
|---|---|---|---|---|---|
| N | n (%(n/N)) | n (%(n/N)) | n (%(n/N)) | n (%(n/N)) | |
| Males | |||||
| Non-positive syphilis tests | 262 800 | 238 376 (90.7) | 243 590 (92.7) | 245 333 (93.4) | 246 502 (93.8) |
| All positive syphilis tests | 18 428 | 13 078 (71.0) | 14 492 (78.6) | 15 571 (84.5) | 16 255 (88.2) |
| ‘Current’ positive syphilis tests | 4298 | 2635 (61.3) | 3099 (72.1) | 3433 (79.9) | 3651 (84.9) |
| ‘Historical’ positive syphilis tests | 14 130 | 10 443 (73.9) | 11 393 (80.6) | 12 138 (85.9) | 12 604 (89.2) |
| Females | |||||
| Non-positive syphilis tests | 262 899 | 240 500 (91.5) | 245 327 (93.3) | 246 669 (93.8) | 247 576 (94.2) |
| All positive syphilis tests | 3494 | 2029 (58.1) | 2351 (67.3) | 2641 (75.6) | 2865 (82.0) |
| ‘Current’ positive syphilis tests | 1256 | 743 (59.2) | 886 (70.5) | 999 (79.5) | 1075 (85.6) |
| ‘Historical’ positive syphilis tests | 2238 | 1286 (57.5) | 1465 (65.5) | 1642 (73.4) | 1790 (80.0) |
‘Current’ positive syphilis tests: DFA-positive or a positive CMIA serology screen with an RPR antibody titre of ≥1:8 were considered more likely to represent current (untreated) syphilis infections; ’historical’ positive syphilis tests: positive CMIA screen with an RPR<1:8 were considered more likely to represent historical (treated/resolved) infections.
CMIA, chemiluminescent microparticle immunoassay; DFA, direct fluorescent antibody; PHO, Public Health Ontario; RPR, rapid plasma reagin.
Positive syphilis tests
Between 2017 and 2022, among males, the proportion of positive syphilis tests that had an HIV test on the same day ±28 days increased from 57.4% to 72.1% among ‘current’ positives (OR 1.13, 97.5% CI (1.05 to 1.22)) and from 66.3% to 80.6% among ‘historical’ positives (OR 1.17, 97.5% CI (1.12 to 1.22), table 1). ‘Current’ positives were consistently less likely than ‘historical’ positives to have had an HIV test on the same day ±28 days (69.1% vs 76.6%, 97.5% CI (−0.084 to −0.066).
Among females, the proportion of ‘current’ positives that had an HIV test on the same day ±28 days increased from 55.5% in 2017 to 70.5% in 2022 (OR 1.16, 97.5% CI (1.11 to 1.22)), but there was no significant time trend among ‘historical’ positives (64.4% overall, table 1). Unlike in males, ‘current’ positives were more likely than ‘historical’ positives to have had an HIV test on the same day ±28 days overall (67.1% vs 64.4%, 97.5% CI (0.0062 to 0.049)), but this varied by year. Between 2017 and 2022 cumulatively, a larger proportion of syphilis tests among males had an HIV test on the same day ±28 days compared with females for both ‘current’ (69.1% vs 67.1%, 97.5% CI (0.00023 to 0.039)) and ‘historical’ positive syphilis tests (76.6% vs 64.4%, 97.5% CI (0.11 to 0.13)) (table 1). Between 2017 and 2022, 5.5% and 7.3% of all positive syphilis tests among males and females, respectively, had no corresponding HIV test regardless of time window (4.9% and 6.0% in 2022 alone). For a detailed breakdown of the results, refer to online supplemental tables 1 and 2.
HIV diagnoses with positive syphilis tests
Among females, between 2017 and 2022, 0.3% of all positive syphilis tests with an HIV test on the same day ±28 days had a positive HIV test result, and there was no difference between ‘current’ and ‘historical’ positive syphilis tests (97.5% CI (−0.0032 to 0.0029), table 3). Among males, however, 1.2% of all positive syphilis tests with an HIV test on the same day ±28 days had a positive HIV test result, and this differed greatly by category of positive syphilis test result—2.7% among ‘current’ positives and 0.8% among ‘historical’ positives (97.5% CI (0.016 to 0.023), table 3). These proportions both decreased over time (OR 0.82, 97.5% CI (0.77 to 0.88) for ‘current’; OR 0.85, 97.5% CI (0.79 to 0.92) for ‘historical’, online supplemental table 4), as the number of positive syphilis tests (denominator) increased for both. When examining within HIV exposure categories, 1.5% of ‘current’ and 0.5% of ‘historical’ positive syphilis tests with an HIV test on the same day ±28 days had a positive HIV test result among males reporting heterosexual contact (97.5% CI (0.004 to 0.017), table 3) compared with 2.9% and 0.7%, respectively, among males reporting male-to-male sexual contact (97.5% CI (0.018 to 0.027)) and 3.4% and 1.5% among males with unknown HIV exposure (97.5% CI (0.0092 to 0.029)). For a detailed breakdown of the results, refer to online supplemental tables 3 and 4.
Table 3. Number of positive syphilis tests with an HIV test on the same day ±28 days (N), and number/proportion with a positive HIV test result (n), by sex, HIV exposure category (among males), and syphilis test result, Ontario, PHO, 2017–2022 (cumulative).
| Positive syphilis tests with an HIV test* | Number/proportion that had a positive HIV test result | |
|---|---|---|
| N | n (%(n/N)) | |
| All positive syphilis tests | ||
| Females | 7795 | 24 (0.3) |
| Males (all) | 53 389 | 665 (1.2) |
| Males with male-to-male sexual contact | 38 589 | 450 (1.2) |
| Males with heterosexual contact | 6226 | 50 (0.8) |
| Males with unknown HIV exposure | 7918 | 159 (2.0) |
| ‘Current’ positive syphilis tests | ||
| Females | 2331 | 7 (0.3) |
| Males (all) | 12 202 | 334 (2.7) |
| Males with male-to-male sexual contact | 7863 | 231 (2.9) |
| Males with heterosexual contact | 2070 | 31 (1.5) |
| Males with unknown HIV exposure | 1981 | 68 (3.4) |
| ‘Historical’ positive syphilis tests | ||
| Females | 5464 | 17 (0.3) |
| Males (all) | 41 187 | 331 (0.8) |
| Males with male-to-male sexual contact | 30 726 | 219 (0.7) |
| Males with heterosexual contact | 4156 | 19 (0.5) |
| Males with unknown HIV exposure | 5937 | 91 (1.5) |
‘Current’ positive syphilis tests: DFA-positive or a positive CMIA serology screen with an RPR antibody titre of ≥1:8 were considered more likely to represent current (untreated) syphilis infections; ‘Historical’ positive syphilis tests: positive CMIA screen with an RPR<1:8 were considered more likely to represent historical (treated/resolved) infections.
HIV test on the same day ±28 days.
CMIA, chemiluminescent microparticle immunoassay; DFA, direct fluorescent antibody; PHO, Public Health Ontario; RPR, rapid plasma reagin.
Discussion
Our results provide insight into adherence to HIV testing guidelines for individuals being tested for syphilis in Ontario. It is encouraging that approximately 9 in 10 non-positive syphilis tests had an HIV test on the same day for both males and females, and since non-positive tests make up the vast majority (>93%) of all syphilis tests, it can be concluded that most syphilis tests in general are indeed accompanied by HIV tests among individuals with no evidence of a previous HIV diagnosis. In contrast, only ~3/4 of all positive syphilis tests among males and ~2/3 among females had an HIV test on the same day ±28 days. Furthermore, only ~7/10 ‘current’ positive syphilis tests among males had an HIV test on the same day ±28 days. One explanation for individuals with positive syphilis tests being less likely to receive timely HIV testing may pertain to these tests representing diagnostic testing among individuals with symptoms and/or known exposures, where providers may be particularly focused on syphilis diagnosis. Further, some of these positive syphilis tests will represent repeat or follow-up tests after diagnosis and treatment of syphilis to monitor treatment progress, where concurrent HIV testing may not have been indicated or, conversely, may have in fact been opportune. It is encouraging that larger proportions of positive syphilis tests did have corresponding HIV tests when applying a larger time window (±180 days). Non-positive syphilis tests may be conducted as a part of comprehensive STI screening among asymptomatic individuals, including those on HIV pre-exposure prophylaxis (PrEP). Providers have previously reported that they may not routinely offer HIV testing due to policy barriers, feeling rushed with patients, fear of offending their patients or the perception that their patient is low risk.18 19
Where HIV testing was performed, individuals positive for syphilis were more likely to be diagnosed as HIV-positive compared with the general population testing for HIV, highlighting the pertinence of this population in identifying undiagnosed individuals living with HIV. In 2022, 0.4% of females positive for syphilis in our study were diagnosed with HIV, compared with 0.05% HIV test positivity among females in the general population (p<0.05).20 This significant difference (p<0.05 for all) was consistent across males with male-to-male sexual contact (0.8% vs 0.31%), heterosexual contact (0.8% vs 0.05%) and unknown HIV exposure (1.6% vs 0.13%). These differences were greater among ‘current’ positive syphilis tests. These results provide further support for the established correlation between syphilis and HIV infections,4 especially among GBMSM.9,11
Many of the risk factors for STIs, including syphilis, overlap with risk factors for HIV and would, therefore, indicate testing for both.21 Accurate assessment of a patient’s risk for HIV can be difficult because patients may hesitate to disclose for fear of stigmatisation or may self-perceive their behaviours to be low risk for HIV acquisition.22 For this reason, the US CDC guidelines state that HIV screening should accompany STI testing, ‘regardless of whether the patient reports any specific behavioural risks for HIV’.8 However, a large dataset from emergency department visits for STI testing in the USA between 2010 and 2018 found that only 1.5% of these encounters included ordering of both syphilis and HIV testing.15 Our findings showed that among positive syphilis tests with HIV tests on the same day ±28 days, males who reported heterosexual contact (and, therefore, no male-to-male sexual contact by virtue of the exposure category hierarchy) were more likely to receive positive HIV test results than their female counterparts (p<0.05). This was an interesting finding in that one might expect more comparable HIV risk with shared heterosexual exposure. Also, males with unknown HIV exposure, who may not have disclosed or been asked about their HIV risk factors, were the most likely to receive positive HIV test results. This dearth in disclosure can preclude sexual health counselling and the provision of prevention options, including PrEP. Our results also demonstrate potential limitations of such self-reported data in clinical settings and provoke questions of how offering testing based only on the self-reported risk of the patient may contribute to missed diagnoses and ongoing transmission. This is tempered, however, with the consideration that risk factors may indeed be discussed but not consistently documented on test requisition forms.
Our analysis is not without limitations. First, individuals’ HIV tests may not always link to their syphilis tests. This has implications for (1) identifying people previously diagnosed with HIV (and exclusion of their syphilis tests) and (2) identifying corresponding HIV tests. Although we employed linkage based on health card numbers (a unique ID for most Ontarians), dates of birth and first and last names, some failed linkages could result from incomplete or inconsistent data or non-nominal HIV testing. The majority of anonymous HIV testing in Ontario is conducted in males (Ontario HIV Epidemiology and Surveillance Initiative, unpublished data, 2024); therefore, males may be more likely to have no linked HIV test. Anonymous testing comprised a relatively small proportion (between 0.8% and 2.4% per year) of HIV tests between 2017 and 2022. Second, given that we were limited to syphilis laboratory testing data alone, we could not distinguish current syphilis infections from treated/resolved infections. Our ‘current’ definition (ie, RPR≥1:8) is a conservative estimate of infectious syphilis that was based on national guidelines and consultation with healthcare providers with syphilis expertise.5 Classification of syphilis test results based on longitudinal analyses was not employed due to the need for historical data (dataset restricted to 6 years), limitations pertaining to patient linkage to enable validation of the longitudinal analysis using case and clinical information and the preference for more simplistic methods intended for surveillance. Our categorisation based on RPR titres is not a validated method and will encompass misclassification on the individual level; however, we believe it to be reasonable for population-level surveillance purposes. To support this, the proportion of individuals with an RPR≥1:8 among individuals tested was 0.97%, which was comparable to the proportion of infectious syphilis cases (identified through public health reporting) among individuals tested (0.71%). The main objective of this analysis was to find opportunities for public health intervention to improve testing for HIV, and we reasoned that any syphilis testing visit could be an opportunity for HIV testing. The rate of syphilis testing in our dataset is approximately 1.16 tests per person per year, which aligns with the recommendation that individuals at risk for HIV be screened at least annually. Lastly, we had incomplete data with respect to HIV exposure category, and these data are subject to recall and social desirability biases, as discussed. This may affect interpretations among exposure categories, especially as males with unknown HIV exposure had the largest proportions with positive HIV test results.
Since most syphilis and HIV testing is centralised at PHO and our analyses used all tests in the study period, our results are representative provincially; however, they may not be generalisable to other jurisdictions.
Conclusions
In conclusion, most individuals who were tested for syphilis in Ontario between 2017 and 2022 were also tested for HIV. Individuals with positive syphilis tests, however, despite some important caveats, were less likely to be tested for HIV compared with individuals non-positive for syphilis, representing a potential opportunity for enhanced HIV testing among those positive for syphilis in accordance with HIV testing guidelines. When tested for HIV, individuals positive for syphilis were considerably more likely to be diagnosed as HIV-positive compared with the general population testing for HIV, especially males, and in particular, males with ‘current’ positive syphilis test results. Ensuring that individuals with positive syphilis results are tested for HIV in a timely manner may identify people living with previously undiagnosed HIV.
Supplementary material
Acknowledgements
The authors would like to acknowledge Ken English, HIV and Hepatitis C Programmes at the Ontario Ministry of Health, for the data request that led to this analysis. We also acknowledge all staff at PHO’s laboratory. PHO’s laboratory and offices are situated on the traditional territory of many nations, including the Mississaugas of the Credit, the Anishinaabeg, the Chippewa, the Haudenosaunee and the Wendat peoples and are now home to many diverse First Nations, Inuit and Métis peoples.
Footnotes
Funding: The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Prepublication history and additional supplemental material for this paper are available online. To view these files, please visit the journal online (https://doi.org/10.1136/bmjopen-2024-097142).
Provenance and peer review: Not commissioned; externally peer reviewed.
Patient consent for publication: Not applicable.
Patient and public involvement: Patients and/or the public were not involved in the design, conduct, reporting or dissemination plans of this research.
Data availability free text: All available data are presented in this manuscript.
Ethics approval: This project did not require research ethics committee approval, as the activities described in this manuscript are considered routine public health practice rather than research. These activities were conducted in fulfilment of Public Health Ontario’s legislated mandate 'to provide scientific and technical advice and support to the healthcare system and the Government of Ontario in order to protect and promote the health of Ontarians…' (Ontario Agency for Health Protection and Promotion Act, SO 2007, c 10, Schedule K).
Data availability statement
All data relevant to the study are included in the article or uploaded as supplementary information.
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