Hepatitis E virus seroprevalence in South Africa from a multi-site study among HIV-negative and HIV-positive adults and age-stratified children (2-17 Years)

A multi-site study in South Africa reveals that Hepatitis E virus seroprevalence is highly heterogeneous, varying significantly by age group and location with the highest rates observed in adults and notable differences between clinical sites, underscoring the need for enhanced surveillance to better understand transmission patterns.

The Gist

Imagine South Africa as a massive, bustling library. For a long time, people knew that a specific "virus book" called Hepatitis E (HEV) existed on the shelves, but they didn't know exactly how many copies were in circulation, who had read them, or if the story changed depending on which section of the library you were in.

This study is like sending a team of librarians to three different branches of that library (Johannesburg, the Western Cape, and Pretoria) to take a headcount of who has a "stamp" in their passport proving they've encountered this virus before. They looked at 859 people, ranging from toddlers (2 years old) to adults (45 years old), including both people living with HIV and those without.

Here is the story of what they found, broken down simply:

1. The Big Picture: A Patchwork Quilt

The researchers found that about 18 out of every 100 people in their study had the "stamp" (antibodies) showing they had been exposed to Hepatitis E in the past.

Think of this like a patchwork quilt. The pattern isn't the same everywhere.

• The "Adults" Patch: Adults had the most stamps. About 27% of them had been exposed.
• The "Teens" Patch: Surprisingly, teenagers (12–17 years) had the fewest stamps, with only about 7% showing exposure.
• The "Little Kids" Patch: Young children (2–5 years) had more stamps than the teens (13%), but fewer than the adults.

The Analogy: Imagine the virus is a popular toy. The adults have collected the most toys over their long lives. The little kids have started collecting some. But the teenagers seem to be in a "gap"—they haven't collected as many as the adults, and they seem to have fewer than the little kids. The researchers suggest this might be because the "toy" (the virus) is passed around differently at different ages, or perhaps the "stamps" (antibodies) from early childhood fade away before the teens get new ones.

2. Location, Location, Location

Where you live mattered a lot. It's like how the weather is different in different parts of the country.

• Johannesburg and the Western Cape: These areas had higher rates of "stamps."
• Pretoria: This area had significantly fewer stamps.

The researchers noted that the virus seems to be more common in some neighborhoods than others, likely due to local factors like water quality, sanitation, or even what people eat (like pork products, which can carry the virus).

3. The HIV Question

A major question was: "Does having HIV change the story?"

• The Finding: People living with HIV had a slightly higher rate of exposure (29%) compared to those without HIV (26%), but the difference was not statistically significant.
• The Takeaway: In this study, having HIV didn't seem to make someone much more likely to have caught Hepatitis E than someone without HIV. The virus didn't seem to be "picking on" the HIV-positive group specifically in terms of how often they got exposed.

4. The "Strength" of the Stamp (Antibody Titers)

The researchers didn't just count who had a stamp; they also measured how "dark" or "faint" the stamp was. This is called the antibody titer.

• The Surprise: The youngest children (2–5 years) had the darkest, strongest stamps (highest antibody levels).
• The Adults: Even though more adults had been exposed, their stamps were much fainter (lower antibody levels).

The Analogy: Think of the antibody level like the ink on a stamp.

• Young Kids: Their ink is fresh and dark, suggesting they might have encountered the virus very recently.
• Adults: Their ink is faded, suggesting they encountered the virus a long time ago, and the "ink" has naturally faded over the years.

This suggests that while adults have a longer history of exposure, the most recent infections are happening in the youngest children.

5. What They Didn't Find

• Gender: Being a boy or a girl didn't really change the odds of having the stamp.
• HIV Health Status: Among the people with HIV, how "strong" their immune system was (measured by CD4 counts) or how much virus was in their blood didn't seem to change their likelihood of having Hepatitis E antibodies.

The Bottom Line

This study is like taking a snapshot of a very complex picture. It tells us that Hepatitis E in South Africa is not a uniform threat; it varies wildly depending on how old you are and where you live.

• Adults have the most history with the virus.
• Teenagers seem to be in a quiet period with less exposure or fading immunity.
• Young children are showing signs of very recent exposure.

The researchers conclude that to stop the virus, we need to understand these local differences better. We can't treat the whole country as one big block; we need to look at the specific neighborhoods and age groups to figure out where the virus is hiding and how it's moving.

Technical Summary

1. Problem Statement

Hepatitis E virus (HEV) is a leading cause of acute viral hepatitis globally, with transmission routes varying by genotype (fecal-oral for genotypes 1/2; zoonotic for genotypes 3/4). While HEV is endemic in South Africa, comprehensive data on seroprevalence across specific demographic subgroups—particularly children and people living with HIV (PLWH)—is scarce. Existing data is often limited by small sample sizes, regional focus, or a lack of age stratification. Furthermore, the interplay between HIV status, immune suppression, and HEV exposure in the South African context remains poorly defined. This study aims to fill these gaps by quantifying anti-HEV IgG seroprevalence and antibody titers across diverse age groups and HIV statuses in multiple geographic locations.

2. Methodology

• Study Design: A prospective, multi-site, cross-sectional assessment conducted as part of a Phase 2b open-label vaccine trial (NCT06306196).
• Study Population: 859 participants recruited from three clinical research centers in South Africa:
  • Be Part Research: Mbekweni, Paarl (Western Cape).
  • Newtown Clinical Research Centre: Johannesburg.
  • Mecru Clinical Research Unit: Garankuwa, Pretoria.
• Cohorts: Participants were stratified into four age groups:
  • Adults (18–45 years): Subdivided into PLWH ($n=178$) and HIV-negative ($n=232$).
  • Adolescents (12–17 years): $n=174$.
  • Children (6–11 years): $n=175$.
  • Young Children (2–5 years): $n=100$.
• Laboratory Analysis:
  • Screening: Anti-HEV IgG was measured using the WANTAI HEV IgG ELISA kit.
  • Quantification: Seropositive samples were quantified using a quantitative ELISA calibrated against the WHO Reference Reagent (NIBSC code: 95/584) to determine antibody titers in IU/mL.
  • HIV Markers: For PLWH, viral load (GeneXpert) and CD4 counts (flow cytometry) were assessed.
• Statistical Analysis: Seroprevalence was compared across sites, age groups, sex, and HIV status using Chi-square/Fisher's exact tests. Logistic regression was used to identify independent predictors of seropositivity, adjusting for covariates.

3. Key Contributions

• Granular Age Stratification: Unlike previous studies focusing on adults, this study provides detailed seroprevalence data for children aged 2–17, revealing distinct patterns of exposure and antibody kinetics in pediatric populations.
• HIV Co-infection Analysis: It offers a specific comparison between PLWH and HIV-negative adults in a setting with high HIV prevalence, assessing whether immune suppression alters HEV exposure or serological response.
• Quantitative Antibody Data: The study moves beyond binary seropositivity by measuring antibody titers, providing insights into the recency of infection and potential antibody waning.
• Multi-Site Geographic Comparison: By sampling from three distinct provinces (Western Cape, Gauteng-Johannesburg, Gauteng-Pretoria), the study highlights significant regional heterogeneity in HEV epidemiology within South Africa.

4. Key Results

• Overall Seroprevalence: The overall anti-HEV IgG seroprevalence was 18.0% (95% CI: 15.6–20.8).
• Age-Related Patterns:
  • Adults (18–45): Highest seroprevalence at 27.3% (29.2% in PLWH vs. 25.9% in HIV-negative).
  • Adolescents (12–17): Lowest seroprevalence at 6.9%.
  • Children: Intermediate rates of 10.3% (6–11 years) and 13.0% (2–5 years).
  • Statistical Significance: Adults had significantly higher odds of seropositivity compared to children (aOR 2.8, $p=0.002$).
• Geographic Variation: Significant site-specific differences were observed.
  • Be Part Research (Western Cape) and Newtown (Johannesburg) showed higher seroprevalence compared to Mecru (Pretoria).
  • For example, in healthy adults, Be Part had 34.5% vs. Mecru's 17.2% ($p=0.0499$).
• HIV Status: While PLWH had a slightly higher seroprevalence (29.2%) than HIV-negative adults (25.9%), the difference was not statistically significant ($p=0.451$). Viral load and CD4 count categories did not significantly predict seropositivity.
• Antibody Titers:
  • Young Children (2–5 years) exhibited the highest mean antibody titers (5.06 IU/mL), suggesting recent or active exposure.
  • Adults had significantly lower mean titers (0.68–0.88 IU/mL) despite higher seroprevalence, indicating older infections with waning antibodies.
  • The difference in titers across age groups was statistically significant ($p=0.0371$).
• Sex Differences: Females had slightly higher seroprevalence (19.4%) than males (16.5%), but this was not statistically significant.

5. Significance and Implications

• Epidemiological Heterogeneity: The study confirms that HEV exposure in South Africa is highly heterogeneous, driven by local environmental, sanitary, and dietary factors rather than a uniform national risk. The lower rates in Pretoria compared to the Western Cape and Johannesburg suggest distinct transmission dynamics.
• Transmission Dynamics: The "U-shaped" or non-linear age pattern (high in young children, low in adolescents, high in adults) suggests a complex transmission landscape. The low adolescent seroprevalence may be due to antibody waning (as seen in longitudinal studies elsewhere) or a temporary reduction in exposure risk during adolescence, rather than a lack of infection.
• Public Health Strategy: The findings underscore the need for integrated HEV surveillance that includes pediatric and HIV-positive populations. The high antibody titers in young children suggest that early-life exposure is significant, potentially informing vaccination strategies for this age group.
• HIV Context: The lack of significant difference in seroprevalence between PLWH and HIV-negative adults suggests that HIV status alone does not drastically alter the likelihood of HEV exposure in this cohort, though PLWH remain a vulnerable group for severe outcomes if infected.

In conclusion, this study provides the most comprehensive baseline data on HEV seroprevalence in South Africa to date, highlighting the necessity for region-specific public health interventions and further research into the mechanisms of antibody waning and transmission in pediatric populations.