Introduction

The availability of rapid screening tests for HIV and other STIs is a key strategy to facilitate the diagnosis of vertical transmission in pregnant women. The World Health Organization (WHO) recommends that pregnant women be tested for HIV, syphilis, and Hepatitis B (HbsAg) at least once during pregnancy preferably in the first trimester. The dual rapid test for HIV infection and syphilis can be used as a first test for pregnant women in prenatal care. The dual rapid test for HIV and syphilis detects antibodies to both Treponema pallidum (the cause of syphilis) and HIV. Like other rapid tests used only for HIV, it does not require refrigeration. At present, available products do not discriminate between active and past syphilis infections. Therefore, if a person has had syphilis that was treated or resolved and anti-treponemal antibodies persist, the HIV rapid dual test for HIV infection and syphilis may be positive for syphilis¹.

These simple tests can be used in the care setting and save costs compared to tests usually done in prenatal care. They enable more women to be diagnosed with HIV and syphilis so that they can access treatment and avoid passing the infection on to their children.

Successful implementation of dual rapid HIV and syphilis tests in prenatal care would increase the rates of syphilis detection to match those of HIV in countries such as India, where rates of syphilis screening in prenatal care increased by 195%, Uganda 119% and 117% in Nigeria, without affecting HIV testing rates².

Although many countries have policies for prenatal syphilis screening, more than 350,000 adverse pregnancy outcomes due to untreated maternal syphilis are reported each year despite the low cost of treatment³. To achieve current targets, efforts have been made to accelerate the elimination of maternal and child transmission of syphilis and HIV.

A study in China assessed the acceptability and feasibility of dual HIV/Syphilis testing in pregnant women at primary health care centers and increased acceptance of tests especially in rural areas⁴.

Prevention of maternal and child transmission of HIV, initially introduced as a vertical program, has also been increasingly integrated into routine prenatal care. Therefore, in many countries and regions, services for the prevention of maternal-child transmission of HIV and syphilis are now provided simultaneously; dual elimination of maternal and child transmission of HIV and syphilis is now a regional strategy in the Americas, Asia-Pacific, Africa, and Europe, and at least 60 countries have integrated strategies for the prevention and elimination of maternal and child transmission of HIV and syphilis⁵.

In general, rapid diagnostic tests (RDTs) are highly sensitive and specific. The WHO compared the performance of eight rapid syphilis tests with a combined treponemal test reference standard and found sensitivities of 84.5-97.7% and specificities of 92.8-98.0%. Comparison of the results of rapid tests among patients at the US STD clinic showed that capillary puncture samples are as good as venous blood samples for detection⁶.

Countries have started using dual HIV and syphilis RDTs in various settings. Many studies have shown satisfactory clinical performance in diagnosing both HIV infection and syphilis-causing infection. The WHO evaluation of this RDP performance as part of the prequalification process showed a final sensitivity of 100% (95% CI 98.2-100%) for HIV antibodies and specificity of 99.5% (95% CI 97.2-100%) compared to the reference analyses. In the case of antibodies against Treponema pallidum, the final sensitivity was 87% (95% CI 81.5-91.3%), with a specificity of 99.5% (95% CI 97.2-100%)⁷.

The advantages of the dual rapid HIV and syphilis test in prenatal care offer the possibility of detecting both infections with a single digital puncture. Results are available quickly, allowing antiretroviral treatment against HIV infection to be started, penicillin treatment benzathine for syphilis, or both if necessary. In addition to increasing the coverage of screening and treatment for syphilis, the dual rapid test can simplify training by providing one test instead of two, and reduce storage space and transport costs, as well as waste disposal. Countries should review the HIV and syphilis rapid dual-test as part of their control and prevention strategy.

The Joint United Nations Programme on HIV/AIDS (UNAIDS) estimated a prevalence of 0.2/100,000 inhabitants aged 15-49 years, with regard to syphilis, has been reported as a prevalence of 0.014/100,000 inhabitants, however, this disease is considered as a reemerging disease among the priority public health problems.

A study conducted in three Instituto Mexicano del Seguro Social (IMSS) delegations demonstrated the validity of the dual rapid test for HIV/Syphilis as a screening test, due to its high sensitivity and specificity found during the study⁸. In Mexico, the incidence of HIV in pregnancy is 0.067%⁹. Screening for HIV during pregnancy is part of routine testing during prenatal monitoring. The offer of testing during pregestational consultation and prenatal monitoring is set out in NOM-007/SSA2-2016 for the care of women during pregnancy, childbirth and puerperium, and of newborns. However, HIV screening coverage in 2016 within the Ministry of Health (SS) was just over 50%, according to estimates by the Censida¹⁰.

The NOM-039-SSA2-2014 for the prevention and control of sexually transmitted infections states that every pregnant woman should be tested for VDRL or RPR and immunofluorescence for Treponema pallidum during the first prenatal visit, regardless of the trimester of pregnancy in which they are, and those in which no tests have been performed, these should be offered before or immediately after delivery, to detect syphilis in pregnant women and to prevent congenital syphilis¹¹.

In the Specific Action Programme under Priority Objective 4, it considers the elimination of vertical transmission of HIV and syphilis with a prevention, timely treatment, and non-discrimination approach (Ministry of Health, 2022). It should be noted that, according to the information reported by the conventional epidemiological surveillance system, during 2022 only 15 cases of vertical transmission of HIV per year of birth were reported, out of a total of 46 cases of vertical transmission¹². In our country, the dual test was started in 2012 at the Mexican Health Department and the Social Security Institute. To use these dual tests, it is required that this be authorized by the Federal Commission for the protection against health risks and included by the Council of General Health in its National Compendium of Health Inputs¹³. The objective of the review was to describe the findings from the application of the dual test for HIV/syphilis (Neogen Dual) the test most frequently used in 2023 in pregnant women who attended health services (SSA and IMSS) of the states and to analyze the frequency and percentage of reactivity and positivity of the test.

Methodology

This is a retrospective, cross-sectional descriptive study of the results found in the application of the dual test for HIV/Syphilis in pregnant women from state health services (health centers) and the Mexican Social Security Institute, ordinary regime (Units of family medicine) FMU by 2023. The population under study were pregnant women who attended prenatal consultation in first-level units of these two institutions during this year. The variables under study were number of rapid duplex tests distributed, tests applied, reactive tests, and confirmed tests. The test most frequently used was the so-called Neogen Dual (HIV and syphilis), reagent for the qualitative chromatographic determination of antibodies against HIV 1 and 2 and Treponema pallidum in serum, plasma or whole blood. With a sensitivity of 99% or more and a specificity of 98% or more for HIV and a sensitivity of not < 95% and a specificity of not < 98% for syphilis, according to the certificate of diagnostic evaluation from the Institute of Epidemiological Diagnosis and Reference.

Information is requested through the National Institute of Information Transparency to the National Centre for Equity and Gender and Reproductive Health of the SSA, and the Medical Benefits Directorate of the Mexican Social Security Institute on the number of dual tests applied during 2023 and how many of these were found to be reactive to the rapid test and were confirmed for HIV and syphilis, respectively.

In parallel, 15 randomly selected states were also asked for the number of reactive tests they had and how many of these were confirmed according to the standard. Only seven states sent information regarding confirmed tests.

The analysis includes calculation of the frequency of application of the duplex test by state and its reactivity rates and confirmation of possible positive cases to HIV/syphilis. We also calculate the prevalence rate found in seven of the 15 states from which we request information on confirmation of diagnosis (STROBE Statement).

Results

According to the National Center for Equity and Gender and Reproductive Health of the Federal Secretariat of Health, 2,004,058 dual tests were distributed throughout the country for the Maternal and Perinatal Health Program in all 32 states. Those tests included in the National Compendium of Health Inputs 2023 with a sensitivity equal to or > 99% and a specificity equal to or > 98% for HIV and a sensitivity not < 95% and a specificity not < 98% for syphilis.

Out of 2,004,058 tests distributed in the states, a total of 728,742 HIV tests (36.4%) and 698,083 (34.8%) for syphilis were applied, the difference observed between the number of HIV/syphilis tests is due to the application of some individual tests. The states of Tamaulipas, Tabasco, Aguascalientes, Hidalgo, Morelos, and Quintana Roo have rates of application or use of tests above 50% for HIV/Syphilis (Table 1). Not being so for the rest of the states.

Of the 728,742 tests applied for HIV, 1,803 cases were detected in the country (0.25%), and the states of have the highest percentage of reactive cases were Veracruz (1.72), Tamaulipas (0.89), Sonora (0.77), San Luis Potosí (0.62), Zacatecas (0.56), Colima (0.51), Baja California Sur (0.49), and Chihuahua (0.42). In the case of syphilis, 4,317 reactive cases (0.65%) were detected from 698,083 tests applied and the states with the highest percentage of reactivity were Veracruz (1.86), Sonora (1.78), Coahuila (1.52), Sinaloa (1.32), Aguascalientes (1.30), Zacatecas (1.24), Nayarit (1.19), Colima (1.12), Chihuahua (1.02), and Tamaulipas (1.0) (Table 2).

Only seven states; San Luis Potosí, Nayarit, Guanajuato, Aguascalientes, Coahuila, Veracruz, and Nuevo León reported on the number of confirmatory tests the percentage of confirmation of reactive tests in these states was 20.8% for HIV and 18.5% for syphilis. (Tables 3 and 4).

The estimated prevalence in the seven states that shared their confirmed test information was 1.19 for HIV and 1.6 for syphilis per 1,000 pregnant women.

In the case of the Mexican Institute of Social Security under the ordinary regime during 2023, 516,916 rapid tests were performed, of which 169 reactive tests were found 0.03%; the states with the highest number of reactive tests were: Tamaulipas (0.23), Nuevo León (0.06), Baja California (0.04), Sinaloa (0.07), Quintana Roo (0.07), and Oaxaca (0.14). A total of 79 reactive tests were confirmed (46.7%), in the states of de Aguascalientes, Michoacán, Puebla, Querétaro, Quintana Roo, Veracruz (South), Zacatecas and Mexico City. They had confirmation rates of 100% (Table 5).

Discussion

If we consider that the calculations for the acquisition of rapid dual tests are based on the request of the states regarding the number of probable annual pregnancies, these figures would indicate that the application of dual rapid tests for the detection of HIV and Syphilis in pregnant women in the country is very low regardless of the availability of tests in the states, this situation could be due to a low offer of the benefit to pregnant women in first level care units such as this one within the NOM-007/SSA2-2016 and factors such as state distribution, staff training, conviction to accept the test among other causes.

The sensitivity and specificity of rapid tests performed in pregnant women are generally adequate; However, a certain number of false positives and negatives persists, which varies according to the prevalence of HIV infection in the population, so the characteristics of the diagnostic equipment, the handling of rapid tests, the type of sample used, and the procedures must be considered health conditions of people. It is recommended that in prenatal care services that have many patients, screening be done through laboratory methods such as the enzyme immunoassay. However, due to the heterogeneity in the supply processes of supplies, laboratory equipment, human resources, and geographical access to the health services of the federal entities of our country, the use of rapid tests should be prioritized.

In the case of the Mexican Institute of Social Security ordinary regime, the results observed are more optimistic than for the state health secretary, since their percentages of reactivity to the test are lower, 0.25 versus 0.03%, this may be because the maternal and child health program control system works better and has greater resources. However, 14 states also did not have desirable confirmatory testing rates.

Another variable that is of utmost importance is the confirmation of reactive tests with confirmatory tests such as Elisa, PCR, Wester Blood, and in the case of syphilis, fluorescent antibody tests against Treponema (FTA ABS) which may not be available. In state laboratories, their installed capacity for processing all dual samples is insufficient. Public health authorities will need to accelerate HIV and syphilis maternal and child care programs, requiring multi-level commitment to promote them, provide adequate resources and reliable procurement systems, and improve training and supervision.

Conclusion

The findings in this study allow us to observe that the Maternal and Child Health program in Mexico, despite having RDTs in sufficient quantities to cover the needs of the states, both in the Ministry of Health and the Mexican Institute of Social Security (IMSS), are no longer used in 50% of pregnant women when they go to the health unit, health center, Hospital or Family Medicine Unit (FMU).

A field study is required to determine what factors prevent these rapid duplex tests from being offered to all pregnant women who come for prenatal care. Likewise, determine if there are resources in these states to confirm those tests that are reactive to Syphilis/HIV to begin comprehensive treatment of one or both diseases according to regulations.

The findings and conclusions in this report are those of the author and do not necessarily represent the official position of the National Center for Equity and Gender and Reproductive Health of the Secretary of Health and to the Directorate of Medical Benefits of the Mexican Institute of Social Security ordinary regime.