High prevalence of female genital schistosomiasis and under-detection by urine microscopy among women of reproductive age in Kilifi County, Kenya

This study in Kilifi County, Kenya, reveals that female genital schistosomiasis affects 36% of women of reproductive age but is largely missed by routine urine microscopy, as 72% of infected women showed no detectable urinary eggs, highlighting the critical need for genital sampling and molecular diagnostics in control strategies.

The Gist

Imagine your body as a bustling city. In this city, there's a tiny, invisible troublemaker called Schistosoma haematobium (a type of parasitic worm). Usually, when we think of this parasite, we imagine it causing trouble in the "plumbing system" (the urinary tract), leading to blood in the urine. Doctors have traditionally looked for these worms by checking the "drainage" (urine) for eggs, much like a plumber checking a pipe for clogs.

But this study reveals a hidden problem: The worms are also setting up shop in the "neighborhood" next door (the female reproductive tract), and the traditional plumbing check is missing them entirely.

Here is the story of the study, broken down simply:

1. The Hidden Invasion (What is FGS?)

Think of the female reproductive system as a quiet garden. When the parasite worms lay their eggs, they sometimes get stuck in the soil of this garden instead of washing out through the pipes. This causes inflammation, pain, and damage to the garden. This condition is called Female Genital Schistosomiasis (FGS).

The scary part? The garden can be full of these damaging eggs, but the pipes (urine) might look perfectly clean.

2. The Detective Work (The Study)

Researchers in Kilifi County, Kenya, decided to play detective. They knew the "pipes" (urine) were being checked, but they suspected the "garden" (genital tract) was being ignored.

• The Old Way: They asked women to give urine samples and looked under a microscope for worm eggs. This is like checking the drain for debris.
• The New Way: They asked women to gently swab their own "garden" (using a high vaginal swab) and tested it with a super-sensitive molecular tool called PCR. This tool is like a metal detector that can find a single tiny screw (parasite DNA) even if it's buried deep in the dirt.

3. The Big Surprise (The Results)

The results were a shock to the system:

• The "Clean Pipe" Illusion: When they used the old microscope method, they found worm eggs in only 13% of the women. It looked like the problem was small.
• The Real Picture: When they used the super-sensitive DNA detector on the swabs, they found that 36% of the women actually had the infection in their reproductive tracts.
• The Disconnect: The most startling finding? 72% of the women who had the infection in their "garden" had absolutely no eggs in their "pipes."

The Analogy: Imagine a house where the kitchen sink is clogged. The plumber checks the sink and says, "All clear!" But he forgets to check the basement, where the pipes are actually bursting and flooding the foundation. That's what happened here. Relying only on urine tests is like only checking the sink and ignoring the basement.

4. Why Does This Matter?

If you only check the urine, you are missing the majority of the women who are suffering. These women might be dealing with:

• Chronic pain and bleeding.
• Difficulty getting pregnant.
• Higher risk of catching HIV or other infections because the "garden" is inflamed and damaged.

Because the standard tests miss them, these women aren't getting the treatment they need, and the infection keeps spreading silently.

5. The Takeaway (What Should We Do?)

The study concludes that we need to change our strategy. We can't just look at the "drainage" (urine) anymore.

• New Tools: We need to start using the "metal detectors" (PCR tests) on genital samples to find the hidden infections.
• New Targets: We need to treat women in specific areas (like the Sabaki and Mleji neighborhoods in the study) where the risk is highest, even if they don't have blood in their urine.
• Better Protection: Improving water and sanitation (WASH) is crucial to stop the worms from entering the water in the first place.

In a nutshell: This study is a wake-up call. It tells us that for a long time, we've been looking for a fire in the wrong room. By checking the right place with better tools, we can finally find the women who are suffering and help them heal.

Technical Summary

1. Problem Statement

Female Genital Schistosomiasis (FGS) is a neglected gynecological manifestation of Schistosoma haematobium infection caused by the deposition of parasite eggs in the female reproductive tract. It leads to chronic inflammation, granulomatous lesions, and severe reproductive health sequelae, including increased susceptibility to HIV/STIs, infertility, and ectopic pregnancy.

• The Diagnostic Gap: Routine diagnosis in endemic regions relies heavily on urine microscopy to detect parasite eggs. However, this method often fails to detect FGS because egg deposition in the genital tract can occur independently of egg excretion in the urine.
• The Knowledge Gap: While S. haematobium is endemic to coastal Kenya, there is a lack of community-based data on the prevalence of FGS among adult women in Kilifi County, and the extent to which routine screening underestimates the disease burden remains unknown.

2. Methodology

Study Design & Setting:

• Type: Cross-sectional study (Phase II of a larger investigation).
• Location: Rural Kilifi County, Kenya (specifically Rabai and Magarini sub-counties), known transmission zones for S. haematobium.
• Population: Women of reproductive age (15–50 years).
• Sample Size: 320 women were selected for Phase II; 261 provided complete data (urine microscopy, genital PCR, and questionnaire) for the final analysis.

Data Collection & Procedures:

• Urine Microscopy: Participants provided urine samples over three consecutive days. Samples were filtered (12 μm) and examined for S. haematobium eggs. Infection intensity was categorized as negative, low (<50 eggs/10ml), or high (≥50 eggs/10ml).
• Genital Sampling: Participants self-collected high vaginal swabs (HVS) and vaginal swabs in private dispensary rooms to ensure privacy and reduce stigma.
• Molecular Diagnostics: DNA was extracted from the swabs and analyzed using Real-time PCR targeting the S. haematobium Dra1 gene. Samples with amplification within 40 cycles (Ct < 40) were considered positive.
• Statistical Analysis: Bivariate analyses (Chi-square, Fisher's exact) and multivariable logistic regression were used to identify risk factors. Polynomial regression was used to assess the relationship between PCR Cycle Threshold (Ct) values and urinary egg counts.

3. Key Contributions

• First Community-Based FGS Data in Kilifi: This study provides the first prevalence estimates of FGS specifically among women of reproductive age in Kilifi County using molecular diagnostics.
• Validation of Molecular Sensitivity: It demonstrates the superior sensitivity of genital PCR compared to traditional urine microscopy for detecting genital involvement.
• Quantification of Under-Detection: The study quantifies the "hidden burden," showing that the vast majority of women with genital infection are missed by standard screening protocols.
• Risk Factor Identification: It identifies specific geographic hotspots (sub-locations) and correlates urinary infection intensity with genital disease, while highlighting that self-reported symptoms are poor predictors of FGS status.

4. Key Results

Prevalence:

• FGS Prevalence: The overall prevalence of PCR-confirmed FGS was 36.0% (94/261).
• Geographic Variation: Prevalence varied significantly by location, ranging from 68.6% in Marikebuni to 25.0% in Mleji. Magarini sub-county had a higher burden (43.3%) than Rabai (26.1%).
• Urinary Infection: Only 13.0% (34/261) of participants had detectable eggs in their urine via microscopy.

Diagnostic Concordance & Discordance:

• Concordance: The agreement between urine microscopy and genital PCR was 70.9%.
• Critical Finding: 72% of women with PCR-confirmed FGS had no detectable eggs in their urine. This confirms that relying solely on urine microscopy leads to massive under-diagnosis of genital disease.
• Ct vs. Egg Count: There was a non-linear relationship between PCR Ct values and mean urinary egg counts ($R^2 = 9.6\%$). High Ct values (low DNA load) were found even in women with no urinary eggs, and low Ct values (high DNA load) did not always correlate with high egg counts, indicating that genital and urinary burdens are biologically distinct processes.

Risk Factors:

• Univariate Analysis: Factors associated with FGS included age (15–25 years), sub-location, water contact behaviors, haematuria, dysuria, and history of schistosomiasis.
• Multivariable Analysis: After adjustment, only sub-location and urinary infection intensity remained independently associated with FGS.
  • Women in Mleji (aOR 6.30) and Sabaki (aOR 3.61) had significantly higher odds of FGS compared to the reference area.
  • Women with low-intensity urinary infections (<50 eggs) had elevated odds of FGS compared to uninfected women, though this was borderline significant (p=0.053).
• Symptoms: Self-reported symptoms like bleeding outside menses and dysuria were associated with FGS in bivariate analysis but lost significance in the multivariable model, suggesting symptoms are not reliable standalone diagnostic markers.

5. Significance and Implications

• Public Health Policy: The findings challenge current schistosomiasis control strategies in Kenya, which rely heavily on urine microscopy and school-based mass drug administration (MDA). The study argues that adult women are a reservoir of infection that is currently invisible to standard surveillance.
• Diagnostic Recommendations: The authors advocate for integrating genital self-sampling and molecular diagnostics (PCR) into reproductive health services and schistosomiasis control programs in endemic areas to accurately identify the burden of FGS.
• Clinical Management: Since symptoms are unreliable, clinical guidelines should move away from symptom-based screening for FGS in endemic zones toward targeted molecular testing for high-risk populations.
• Future Interventions: Strengthening Water, Sanitation, and Hygiene (WASH) interventions in identified hotspots (e.g., Sabaki and Mleji) is critical to reducing transmission. Additionally, preventive chemotherapy programs must expand coverage to adult women to address both urinary and genital pathology.

Conclusion:
This study reveals a substantial, previously unquantified burden of Female Genital Schistosomiasis in Kilifi County. It establishes that routine urine microscopy is insufficient for detecting genital disease, as nearly three-quarters of infected women are asymptomatic regarding urinary egg excretion. The integration of molecular diagnostics into surveillance is essential to prevent long-term reproductive morbidity in this population.