PREVALENCE AND FACTORS ASSOCIATED WITH FALSE NEGATIVE RAPID DIAGNOSTIC HIV TESTS AMONG PATIENTS ON ANTIRETROVIRAL THERAPY WITH A NON-DETECTABLE VIRAL LOAD IN KAMPALA, UGANDA: A CROSS-SECTIONAL STUDY

This cross-sectional study conducted in Kampala, Uganda, reveals that approximately 3.2% of patients on antiretroviral therapy with undetectable viral loads yield false-negative results on rapid HIV diagnostic tests, a phenomenon significantly associated with higher CD4 counts and longer duration on treatment, suggesting that serial rapid testing alone may be insufficient for this population.

The Gist

🧐 The Big Picture: The "False Alarm" Problem

Imagine you have a very reliable security guard (the HIV test) who checks your ID at the door of a club. For years, this guard has been excellent at spotting people who don't belong.

However, this study discovered a strange glitch: For some people who have been inside the club for a long time and have been behaving perfectly (taking their medication), the security guard suddenly stops recognizing them.

The guard looks at their ID, shrugs, and says, "You're not on the list. You're clean." But the person is actually on the list; they just look different now because they've been inside for so long. This is called a False Negative.

📍 The Story: What Happened in Kampala?

Researchers in Kampala, Uganda, decided to investigate this glitch. They gathered 1,248 people who:

1. Were living with HIV.
2. Were taking their medication (ART) perfectly.
3. Had successfully suppressed the virus so much that it was "undetectable" (like a ghost that can't be seen).

They put these 1,248 people through the standard "serial testing" process. This is like running them through three different security checkpoints in a row to make sure the first one didn't make a mistake.

The Shocking Result:
Out of 1,248 people who definitely had HIV, the standard tests said 40 of them were HIV-negative.

• The Rate: About 3 out of every 100 people got this wrong result.
• The Danger: If a patient hears "You're negative," they might think, "Wow, I'm cured!" and stop taking their life-saving medicine. This is dangerous because the virus could wake up and start attacking again.

🔍 Why Did This Happen? (The "Why" Behind the Glitch)

The researchers looked for clues to see who was most likely to get this false result. They found two main factors, which we can explain with analogies:

1. The "Long-Term Resident" Effect (Duration on ART)

• The Finding: The longer someone had been on medication, the more likely they were to get a false negative.
• The Analogy: Imagine a chameleon that has lived in a specific forest for 10 years. Over time, its skin has blended in so perfectly with the trees that a human eye can no longer spot it.
  • In the body, long-term medication suppresses the virus so effectively that the body stops producing as many "flags" (antibodies) that the test looks for. The test is looking for the flags, but the flags have faded away, so the test thinks the virus isn't there.

2. The "Strong Immune System" Paradox (CD4 Count)

• The Finding: People with higher CD4 counts (a measure of immune health) were slightly more likely to get a false negative.
• The Analogy: Think of the immune system as a police force. When the virus is active, the police are screaming and waving red flags (high antibody levels). When the virus is suppressed, the police relax. If the police force is very strong and healthy (high CD4), they might calm down too much, making it hard for the test to find any evidence of the past crime.

⚠️ Why Should We Care?

This isn't just a science trivia question; it's a real-world safety issue.

• The Misunderstanding: If a patient gets a "Negative" result, they might think they are cured.
• The Consequence: They stop taking their pills.
• The Result: The virus wakes up, the patient gets sick again, and they can pass the virus to others.

💡 The Solution: What Should We Do?

The researchers are saying: "Don't trust the quick test alone for these specific people."

• The Old Way: Run the rapid test. If it's negative, stop.
• The New Recommendation: If a patient has been on treatment for a long time and tests negative on the rapid test, do not stop there. You must run a more sensitive, "gold standard" test (like a DNA test or ELISA) to double-check.

🏁 The Takeaway

Think of the standard HIV rapid test as a metal detector. It's great at finding metal (the virus) in most situations. But for people who have been "clean" for a very long time, the metal has rusted away or become so small that the detector misses it.

This study is a warning to doctors and patients: Just because the metal detector didn't beep doesn't mean the metal isn't there. We need to use a more sensitive tool to be sure, especially for those who have been successfully managing their health for years.

Technical Summary

1. Problem Statement

Despite the global success of the "Test and Treat" strategy, a critical diagnostic challenge has emerged in Sub-Saharan Africa: false-negative results on Rapid Diagnostic Tests (RDTs) among People Living with HIV (PLHIV) who have achieved viral suppression (undetectable viral load) through long-term Antiretroviral Therapy (ART).

• The Mechanism: Long-term ART leads to the waning of HIV antibodies, causing standard antibody-based RDTs to fail to detect the virus, even though the patient remains infected.
• The Consequence: Patients may be misdiagnosed as HIV-negative, leading to confusion, premature discontinuation of life-saving ART, viral rebound, and increased transmission risks.
• The Gap: While this phenomenon is documented in children and adolescents, there is limited data on adult populations in Sub-Saharan Africa, necessitating local evidence to inform testing algorithms and clinical guidelines.

2. Methodology

• Study Design: Cross-sectional study conducted between October 2023 and February 2024.
• Setting: Kisenyi Health Center IV, a high-volume public ART clinic in Kampala, Uganda.
• Study Population:
  • Inclusion: 1,248 PLHIV aged ≥18 months (caregiver consent for children), currently on ART, with confirmed undetectable viral loads.
  • Exclusion: Patients with detectable viral loads, those who interrupted ART in the last year, or those with advanced disease (Stage III/IV).
• Testing Algorithm (The Core Procedure):
  1. Screening: Participants underwent the national serial rapid testing algorithm:
     • Screening: Determine™ HIV-1/2.
     • Confirmatory: Stat-Pak®.
     • Tie-breaker: SD Bioline®.
  2. Gold Standard Confirmation: Any sample yielding a negative result on the serial RDTs was subsequently tested using a fourth-generation Enzyme-Linked Immunosorbent Assay (ELISA) (Architect HIV Ag/Ab Combo Assay).
  3. Definition of Outcome: A "False Negative" was defined as a negative result on the serial RDT algorithm that was confirmed as positive by the ELISA.
• Data Analysis: Logistic regression (unadjusted and adjusted) was performed using STATA v14.0 to identify factors associated with false-negative results. Variables with $p < 0.2$ in unadjusted models were included in the multivariable model.

3. Key Results

• Prevalence:
  • Among 1,248 participants with undetectable viral loads, 40 (3.2%) tested negative on the serial rapid testing algorithm but were confirmed positive by ELISA.
  • 95% Confidence Interval (CI): 2.20% – 4.20%.
• Demographics:
  • Median age: 34.0 years (IQR: 29.0–42.5).
  • 76.8% Female; 58.0% Married/Living with a partner.
  • 96.9% were on TDF/3TC/DTG (Integrase inhibitor-based) regimens.
  • Median duration on ART: 6 years (IQR: 4.0–9.0).
• Factors Associated with False Negatives (Multivariable Analysis):
  • CD4 Count: Higher CD4 counts were significantly associated with false negatives. For every unit increase in CD4 count, the odds of a false negative increased by 0.1% (Adjusted Odds Ratio [aOR]: 1.001; 95% CI: 1.001–1.003; $p=0.01$).
  • Duration on ART: Longer duration on ART was associated with a lower likelihood of false negatives (aOR: 0.884; 95% CI: 0.801–0.978; $p=0.02$). Conversely, shorter duration on ART increased the risk of false negatives.
  • Non-Significant Factors: Age, gender, marital status, education, BMI, adherence, and comorbidities were not significantly associated with false-negative results in the adjusted model.

4. Key Contributions

• Quantification of Risk: The study provides robust local evidence that approximately 3 in every 100 virally suppressed PLHIV in Uganda will receive a false-negative result on standard rapid testing.
• Algorithmic Limitation: It demonstrates that the current national serial RDT algorithm is suboptimal for re-testing or verifying diagnosis in patients with long-term viral suppression.
• Clinical Correlates: It identifies that patients with higher CD4 counts and those on shorter durations of ART (specifically those recently switched to Dolutegravir-based regimens) are at higher risk. This suggests that the rapid decline in antibody titers is more pronounced in these specific subgroups.
• Policy Implication: The findings challenge the reliance on RDTs alone for monitoring HIV status in suppressed patients, highlighting a critical gap in current "Test and Treat" monitoring protocols.

5. Significance and Recommendations

• Clinical Practice: Healthcare providers must exercise extreme caution when interpreting negative RDT results in patients known to be HIV-positive and virally suppressed. A negative RDT should not be used to rule out HIV infection in this population.
• Guideline Revision: The study recommends that for any PLHIV on ART who tests negative on rapid tests, further confirmatory testing (such as ELISA or HIV DNA/RNA PCR) is mandatory before considering a change in diagnosis or treatment status.
• Future Research: The authors call for longitudinal studies to investigate other factors, including Pre-Exposure Prophylaxis (PrEP) use, specific antibody characteristics, and the impact of different ART regimens on seroreversion rates.
• Public Health Impact: Addressing this diagnostic gap is crucial to preventing unintended treatment interruptions, which could lead to viral rebound and undermine the goal of ending the HIV epidemic by 2030.

Conclusion: The study concludes that false-negative rapid tests are a significant, measurable phenomenon in Uganda's ART population. Relying solely on serial rapid testing for patients with undetectable viral loads is insufficient; confirmatory laboratory testing is essential to prevent misdiagnosis and treatment cessation.