Comparative evaluation of HIV testing interventions for men who have sex with men in the Netherlands: insights for a low-incidence setting

This study uses an agent-based model to demonstrate that combining HIV testing for immigrating men who have sex with men (MSM) upon entry with increased testing frequency (every 7 months) among resident MSM in the Netherlands offers the most effective strategy for reducing new HIV infections in this low-incidence setting.

The Gist

Imagine the HIV epidemic among gay and bisexual men (MSM) in the Netherlands as a leaky boat.

For years, the crew (public health officials) has been doing an amazing job plugging the biggest holes. Thanks to great medicine (like PrEP and treatment), the water level has gone down significantly. But the boat isn't dry yet; it's still leaking a little bit, and the water level has stopped dropping—it's hit a "plateau."

The researchers in this paper asked: "How do we stop the last few leaks?"

They realized there are two main ways water is getting in:

1. The "Local Leak": Water seeping in from the people already on the boat (residents).
2. The "New Passenger Leak": Water dripping in from people just climbing aboard (immigrants) who might be carrying a hidden bucket of water (an undiagnosed infection) from their journey.

Here is how they tested different ways to fix the boat, explained simply:

The Three Strategies They Tested

The team built a giant computer simulation (a "digital twin" of the Dutch MSM community) to test three ideas over the next 15 years:

1. The "Welcome Mat" Test (Testing Immigrants)

• The Idea: When new MSM arrive in the Netherlands, offer them an HIV test right at the airport or border before they even get settled.
• The Metaphor: Imagine checking every new passenger for a hidden leak before they step onto the deck.
• The Result: It helps! If half of the new passengers take the test, it stops about 94 new infections over 15 years. It's a good, efficient fix, but it doesn't stop the most water.

2. The "High-Risk" Net (Testing People with Many Partners)

• The Idea: Only test people who have had a lot of casual partners recently (e.g., more than 5 or 10 in the last 6 months). This is the current "standard" advice.
• The Metaphor: Only checking the people on the boat who are running around the deck the most, assuming they are the ones most likely to splash water.
• The Result: This stops about 340 infections. It's better than just testing new arrivals, but it misses a lot of people.

3. The "Whole-Boat" Net (Testing Everyone More Often)

• The Idea: Encourage everyone on the boat to get tested every 7 months, regardless of how many partners they had.
• The Metaphor: Instead of just checking the runners, we ask everyone to check their pockets for leaks every few months.
• The Result: This is the winner. By testing everyone more frequently, they stopped about 508 infections.

The "Super Combo" Strategy

The researchers found that the absolute best way to keep the boat dry is to do both:

• Check the new passengers at the door (Immigration testing).
• AND check everyone on the boat every 7 months (General testing).

The Result: This combination stops about 534 infections.

The Big Surprise: "Risk" is Harder to Spot Than We Thought

Here is the most important lesson from the paper, explained with a simple analogy:

Imagine you are looking for a thief in a crowd.

• Old Strategy: You only look at people who look "shifty" or are running around a lot (people with many partners).
• New Reality: The study found that many people who don't look "shifty" (people with few partners) are actually the ones carrying the infection. They might have been infected a long time ago and never got tested.

Because the epidemic is now "low" (there are fewer cases overall), the old rule of "only test the high-risk guys" isn't catching enough people. The "thieves" are hiding in plain sight among the quiet people. To find them, you have to cast a wider net and check more people, even if they seem low-risk.

The Bottom Line

• Testing new arrivals is smart and efficient, but it's not enough on its own.
• Testing everyone more often (every 7 months) is the most powerful tool, even though it requires more tests overall.
• The Best Plan: Combine both. Welcome new people with a test, and remind everyone already there to get checked regularly.

Why does this matter?
Finding HIV early is like finding a leak early. If you find it early, you can fix it immediately with medicine, and the person won't pass the water to anyone else. This saves lives and keeps the boat (the community) safe and dry.

The paper concludes that in a world where people move around a lot, we can't just focus on the people who live here; we have to look at the whole picture, including the people just stepping on board.

Technical Summary

1. Problem Statement

Despite significant progress in the Netherlands, where over 96% of men who have sex with men (MSM) living with HIV are diagnosed and virally suppressed, new HIV diagnoses have plateaued. In 2024, 29% of new diagnoses occurred in individuals with late-stage HIV infection, indicating a critical gap in early detection. Furthermore, in low-incidence settings like the Netherlands, a growing proportion of new transmissions is driven by infections introduced via immigration rather than local transmission networks. Current testing guidelines, which often target individuals based on high partner counts (e.g., >10 partners in 6 months), may be insufficient to capture undiagnosed cases in this evolving epidemiological landscape. The study aims to evaluate and compare the impact and efficiency of various testing strategies targeting both resident MSM and incoming immigrants to determine optimal interventions for sustaining the decline in HIV incidence.

2. Methodology

The researchers employed an agent-based model (ABM) of HIV transmission among MSM in the Netherlands, extending a previously developed framework to include explicit, risk-stratified testing modules.

• Model Structure:

  • Population: Simulates 25,000 agents (scaled to 200,000 MSM) aged 15–75.
  • Dynamics: Includes demographic processes (birth, death, aging), dynamic sexual networks (steady and non-steady partnerships), and HIV epidemiology (transmission, progression, care cascade, PrEP).
  • Immigration: Explicitly models the entry of MSM immigrants, distinguishing between those diagnosed (95% virally suppressed) and those undiagnosed. The annual inflow of undiagnosed HIV cases from abroad was calibrated to surveillance data (median 39 cases/year).
  • Testing Logic: Testing frequency is stratified by the number of non-steady partners in the last 6 months (0–2, 3–4, 5–10, >10) and PrEP usage status.

• Intervention Scenarios (2026–2040):
  The study simulated 15-year projections comparing a baseline (current practices) against several intervention strategies:

  1. Entry Testing: Offering a one-time HIV test to incoming MSM at the point of entry with varying uptake rates (10% to 75%).
  2. Targeted Resident Testing: Increasing testing frequency for residents with high partner counts (>5 or >10 partners) to intervals of every 5 years, 23 months, or 7 months.
  3. General Resident Testing: Increasing testing frequency for the entire non-PrEP resident MSM population to a minimum of every 7 months.
  4. Combined Strategies: Pairing entry testing with either targeted or general resident testing.

• Evaluation Metrics:

  • Impact: Cumulative number of new HIV infections averted over 15 years.
  • Efficiency: Average number of additional HIV tests required per infection averted.
  • Analysis: Pareto frontier analysis was used to identify optimal trade-offs between impact and efficiency.

3. Key Contributions

• Integration of Immigration Dynamics: The study explicitly quantifies the role of imported HIV infections in sustaining transmission in a low-incidence setting, a factor often overlooked in domestic-focused models.
• Re-evaluation of Risk Criteria: It challenges the efficacy of strictly targeting high-partner-count individuals, demonstrating that broader testing strategies may yield greater public health returns in low-prevalence contexts.
• Comparative Efficiency Analysis: Provides a granular comparison of "entry-point" interventions versus "resident-focused" interventions, offering specific guidance on resource allocation (tests per infection averted).

4. Key Results

• Impact of Entry Testing: Offering a one-time test to incoming immigrants averted a maximum of 94 infections (95% QI: -128 to 328) over 15 years, assuming a 50% uptake rate. Increasing uptake to 75% did not significantly improve outcomes due to diminishing returns.
• Impact of Resident Testing:
  • General Population: Increasing testing frequency for the entire general MSM population to every 7 months achieved the largest reduction, averting 508 infections (95% QI: 292–900).
  • Targeted (High Risk): Increasing testing for those with >5 partners to every 7 months averted 340 infections (95% QI: 132–592).
  • Targeted (Very High Risk): Targeting those with >10 partners was less effective (256 infections averted).
• Combined Strategy: The most effective strategy combined entry testing (50% uptake) with general resident testing (every 7 months), averting 534 infections (95% QI: 308–884).
• Efficiency Trade-offs:
  • Entry testing was the most efficient intervention (approx. 480 tests per infection averted at 50% uptake).
  • General resident testing was less efficient (approx. 3,305 tests per infection averted) but prevented the highest absolute number of infections.
  • Pareto Frontier: The analysis revealed that while combination strategies offer the highest total impact, the marginal cost (tests required) increases significantly as the number of averted infections exceeds 400.

5. Significance and Implications

• Policy Shift: The findings suggest that in low-incidence settings, relying solely on behavioral risk criteria (e.g., partner count) is suboptimal. Broadening testing to the general MSM population, even those with fewer partners, is necessary to capture undiagnosed cases with long-standing infections.
• Dual-Pronged Approach: The optimal public health strategy involves a combination of entry-point testing for immigrants (highly efficient for early detection and linkage) and frequent, broad testing for residents (maximizing total infections averted).
• Equity and Access: The study highlights that migrants face barriers to care and may not fit traditional risk profiles. Entry-point testing serves as a crucial mechanism to bridge this gap, ensuring faster linkage to care for a vulnerable subpopulation.
• Future Directions: The authors emphasize the need for more detailed data on migrant-specific behaviors (mixing patterns, PrEP access) to refine future models and interventions.

In conclusion, the paper argues that to further reduce HIV transmission among MSM in the Netherlands, public health strategies must evolve from narrow, risk-based targeting to a comprehensive approach that addresses both the domestic population's testing frequency and the specific vulnerabilities of the immigrant population.