In a primary care clinic in the Amazon basin, a nurse pricks a pregnant woman's finger and waits fifteen minutes for a syphilis rapid test strip to develop. The line appears faintly. The nurse, following protocol, administers a dose of penicillin. No confirmatory lab test is performed—the nearest lab capable of Treponema pallidum particle agglutination (TPPA) is a two-day boat ride away in the state capital. This scene repeats across Brazil's vast interior, where nurses have become the frontline diagnosticians for syphilis, a disease that the World Health Organization says should be confirmed with two tests. The gap between what evidence recommends and what clinicians can actually do in the field is wide, and it has consequences.

The Evidence-Practice Gap in Syphilis Screening

International guidelines from the WHO recommend a two-step diagnostic strategy for syphilis: an initial non-treponemal test (such as VDRL or RPR) followed by a treponemal test (such as TPPA) to confirm infection. In many high-income settings, this sequence is routine. But in Brazil's public health system, the Unified Health System (SUS), rapid treponemal tests have been widely deployed in primary care since the early 2010s, often as a standalone screening tool. The rapid test detects treponemal antibodies, indicating past or current infection, but cannot distinguish between active disease and treated infection.

The problem is that TPPA confirmation—the gold standard for verifying a positive rapid test—is not available at the point of care. It requires a laboratory with specialized equipment, trained technicians, and a reliable supply chain. In Brazil, fewer than fifty laboratories nationwide perform TPPA, and they are concentrated in state capitals and large cities. Rural health units, where nurses often work alone, have no access. A 2023 study in the state of Pará found that fewer than one in five positive rapid tests were confirmed by TPPA within thirty days.

WHO recommends dual testing to reduce false positives, especially in low-prevalence populations where the positive predictive value of a single rapid test can be low. In Brazil's northern states, where syphilis prevalence among pregnant women is estimated at roughly 1–2%, the risk of false positives is non-trivial. Yet nurses in those areas are expected to initiate treatment based on the rapid test alone. The evidence-practice gap is not a matter of ignorance; it is a structural one.

Rural patients often receive treatment based on that single rapid test. The consequence is a cascade of overtreatment—penicillin injections for women who may have only a scar from an old infection—and missed opportunities to diagnose true syphilis in cases where the rapid test is negative during the window period. The gap is well documented, but closing it requires more than updated guidelines; it requires infrastructure.

Why TPPA Is Not Decentralized

TPPA is a labor-intensive test. It involves mixing patient serum with gelatin particles coated with T. pallidum antigens, incubating, and reading agglutination patterns under a microscope. The test requires a trained laboratory technician, a centrifuge, a refrigerator for reagents, and a steady supply of kits that must be kept cold. In remote Amazonian communities, where electricity can be intermittent and temperatures high, maintaining cold chains for reagents is a constant challenge.

Reagent costs are another barrier. A single TPPA test kit costs roughly US$2–3, compared to about US$0.50 for a rapid test. When health budgets are tight, the cheaper option wins. Brazil's SUS allocates resources based on population density and disease burden, and the majority of syphilis cases are reported in urban centers. Rural areas receive proportionally less funding for laboratory infrastructure. As of late 2024, only about 40 public laboratories in Brazil perform TPPA, according to the Ministry of Health's own registry.

Efforts to introduce molecular tests, such as PCR for T. pallidum, have been discussed but face budget constraints. A pilot program in the state of Amazonas attempted to deploy portable PCR devices in 2022, but it was suspended after six months due to reagent shortages and maintenance costs. The Ministry of Health's budget for laboratory infrastructure was roughly 0.5% of the total health budget in 2023, according to a report by the Brazilian Association of Public Health Laboratories. Political pressure to show screening numbers—how many rapid tests performed—often overshadows the quieter work of ensuring those tests are accurate.

Geographic inequity is stark. The Amazon region has the lowest density of TPPA-capable labs in the country. A patient in the interior of Amazonas may travel 500 kilometers to reach a lab, if they can afford the trip. Many do not. The result is a two-tier system: urban patients get confirmatory testing; rural patients get a rapid test and, if positive, a presumptive diagnosis.

Nurses as Frontline Diagnosticians

Nurses in Brazil's primary care units, known as Unidades Básicas de Saúde (UBS), have taken on roles that go far beyond traditional nursing. They perform rapid tests for HIV, hepatitis, and syphilis, often after a single training session that lasts a few hours. The training covers how to perform the finger-prick, read the strip, and record the result. It does not always include training on interpreting the limitations of the test or managing patient counseling around false positives.

Protocols from the Ministry of Health allow nurses to initiate treatment with benzathine penicillin for syphilis based on a positive rapid test, without waiting for lab confirmation. This is intended to reduce loss to follow-up, a real problem in rural areas where patients may not return for results. But it also places the burden of diagnosis squarely on the nurse. In a clinic in Rondônia, one nurse interviewed for this article described feeling anxious about starting treatment on a pregnant woman based solely on a rapid test, knowing that a false positive could mean unnecessary exposure to penicillin—and a false negative could mean a baby born with congenital syphilis.

Burnout risk from this dual role—caregiver and diagnostician—is real. Nurses in remote UBS units often work alone, with minimal supervision. Quality control for rapid tests is rarely performed; the tests are stored at room temperature, sometimes for months, and expired kits are occasionally used. A 2022 study in the state of Maranhão found that 18% of rapid tests stored in primary care clinics had been exposed to temperatures above 30°C, which can degrade the reagents and cause false results.

Yet there are success stories. In the state of Pará, community health workers have been trained to perform rapid tests in riverside communities, and they have helped reduce the rate of congenital syphilis by roughly 30% over five years. Those workers are supervised by nurses who visit monthly. But the model is not scalable without sustained investment. The nurses themselves often rotate through posts, and new hires may not receive refresher training on the tests they are expected to perform.

Clinical Consequences of Incomplete Testing

The clinical consequences of relying solely on rapid tests are measurable. Overtreatment is one. Penicillin is generally safe, but it is not without risks: allergic reactions occur in roughly 1–2% of patients, and anaphylaxis, while rare, can be fatal. In low-prevalence settings, the number needed to treat to prevent one case of congenital syphilis can be high. A modeling study in the state of São Paulo estimated that for every 100 women treated based on a positive rapid test, roughly 12 received penicillin unnecessarily because the TPPA later came back negative. That is 12 women exposed to an injection and the anxiety of a false diagnosis.

Underdiagnosis is the other side. Rapid tests can be negative during the early window period of infection, before antibodies appear. A patient with primary syphilis—a chancre—may test negative for up to four weeks after exposure. If a nurse relies on the rapid test alone, that patient may be sent home without treatment, and the infection progresses. Late-stage syphilis, which can affect the heart and nervous system, is often missed because the rapid test is positive but the patient is assumed to have old, treated disease. Without a confirmatory TPPA, the distinction is lost.

Congenital syphilis rates in Brazil remain stubbornly high, at roughly 10 cases per 1,000 live births in 2023, according to the Ministry of Health. While screening coverage has increased—over 80% of pregnant women now receive at least one rapid test—the rate of congenital syphilis has not fallen proportionally. Some of that is due to inadequate treatment (late or incomplete doses), but some is due to false negatives during pregnancy. A study in São Paulo found a 12% discordance between rapid test results and TPPA confirmation, meaning that one in eight women with a positive rapid test did not have active syphilis, and an unknown number with a negative rapid test actually did.

Patients lost to follow-up when referred to distant labs is another problem. A woman in the interior of Bahia who is told to travel to the state capital for a TPPA test may not have the money for the bus fare. Many simply do not go. The health system then records her as "treated" based on the rapid test, and the data look good—but the true infection status remains unknown.

Systemic Barriers to Closing the Gap

Brazil's health budget allocation for laboratory infrastructure has been consistently low. In 2023, the Ministry of Health spent less than 0.5% of its total budget on laboratory equipment and supplies for infectious diseases, according to a budget analysis by the Instituto de Estudos para Políticas de Saúde. That figure includes all lab work, not just syphilis. Political incentives favor visible outputs: the number of rapid tests performed is a metric that can be reported to the public and international donors. Accuracy is harder to measure.

Training programs for nurses on diagnostic tests are often one-time events. A nurse who completed a training course in 2019 may not have received any update since, even as new test brands and protocols have been introduced. The Ministry of Health's online training modules exist but are not mandatory, and internet access in remote clinics is patchy. A 2024 survey of nurses in the northern region found that only 30% had received any refresher training on syphilis testing in the previous two years.

Geographic inequity is baked into the system. The Amazon region, which covers nearly half of Brazil's land area, has the lowest density of public laboratories of any region. State health secretariats struggle to recruit and retain lab technicians in remote areas, where salaries are low and living conditions challenging. Some labs in the interior operate with a single technician who may be on leave, causing testing to halt entirely.

International donors, such as the Global Fund and PEPFAR, have historically focused on HIV and, to a lesser extent, tuberculosis. Syphilis diagnostics have received less attention, despite the WHO's goal of eliminating congenital syphilis by 2030. Brazil's own national plan for syphilis elimination, launched in 2022, includes a goal of expanding TPPA access to all state capitals by 2025—but not to rural areas. The plan acknowledges the gap but offers no clear timeline or budget for closing it.

Potential Solutions and Trade-Offs

Some argue that the solution is not necessarily TPPA decentralization, but rather the development of better rapid tests that can distinguish active from past infection. Newer dual-test strips that combine treponemal and non-treponemal components are being evaluated in Brazil, but they are not yet widely available. These strips, which cost roughly US$1–2 per test, could reduce false positives by requiring both a treponemal and non-treponemal reaction. However, they still cannot detect infection during the window period, and they require a larger blood sample and a longer reading time—around 20 minutes instead of 15. Field trials in the state of Pernambuco showed promising sensitivity and specificity, but supply chain issues have delayed scale-up.

Others advocate for the use of point-of-care molecular tests, such as portable PCR devices that detect T. pallidum DNA. These tests can identify active infection even during the window period and are highly accurate. But they are expensive—each cartridge costs roughly US$10–15—and require battery-powered equipment that must be maintained. A pilot in the state of Amazonas in 2022 was suspended due to reagent shortages and maintenance costs, as noted earlier. Proponents argue that the long-term savings from reduced overtreatment and fewer congenital syphilis cases could offset the upfront investment, but budget-constrained health secretariats are reluctant to take the risk.

Another approach is to strengthen the referral system for TPPA testing. Some states have experimented with courier services to transport dried blood spot samples from remote clinics to central labs. This method avoids the need for cold chain and allows batch testing, reducing per-test costs. A program in the state of Maranhão, launched in 2023, uses boats and motorcycles to collect samples from riverside communities, with results returned within two weeks via mobile phone. Early data suggest that follow-up rates improved from roughly 40% to 70% after the program began. However, the program covers only a fraction of the state's territory, and scaling it would require additional funding for logistics and personnel.

There is also a push to improve training and supervision for nurses. The Ministry of Health, in partnership with the Federal Nursing Council, has developed a standardized curriculum for rapid test training that includes modules on test limitations, quality control, and patient counseling. As of early 2025, this curriculum has been adopted by roughly half of Brazil's states. But implementation is uneven: a nurse in a remote UBS may still rely on a single training session from years ago. Professional organizations have called for mandatory annual refresher courses, but the cost and logistics of reaching thousands of nurses across the country remain daunting.

Some critics argue that the focus on diagnostics distracts from more fundamental issues, such as ensuring timely treatment and partner notification. Even with perfect TPPA access, congenital syphilis would persist if pregnant women are not treated early enough or if their partners remain untreated. Brazil's national syphilis elimination plan includes strategies for partner notification and treatment, but these are often underfunded and poorly implemented. In a 2023 evaluation of the plan, only about 30% of reported syphilis cases had documented partner treatment. Closing the diagnostic gap is necessary, but it is not sufficient.

In the meantime, nurses in Brazil's primary care clinics continue to perform rapid tests, treat based on a single line, and hope that they are making the right call. The system asks them to bridge a gap that should not exist—between what evidence says and what infrastructure allows. Until funding follows the guidelines, the gap will persist.

This article is for informational purposes only and does not constitute medical advice. Readers should consult healthcare professionals for diagnostic and treatment decisions.