Helicobacter pylori: Global Prevalence and Socioeconomic Determinants

Helicobacter pylori is found in every human population where it's been sought.
Wealthier countries have lower prevalences than poorer countries, showing a link between acquisition/spread and socioeconomic conditions.
In children, the disparities are especially stark: in Australia, very few children acquire Helicobacter; in poor countries, acquisition is almost ubiquitous.
Prevalence varies within countries and even within cities; it also varies with age and with childhood socioeconomic status (SES).
The risk of infection is inversely related to childhood SES: $P<em>{ ext{HP}} \propto \frac{1}{\text{SES}</em>{\text{childhood}}}$

Helicobacter pylori evolved with modern humans; sophisticated genetic studies show parallels between human migration and Helicobacter distribution, with mapping of human migration partially inferred from Helicobacters (notably in regions like The Pacific).
The organism has co-evolved with humans for millennia and has also colonized some animals, but human H. pylori is a distinct subspecies from animal strains, and there is no clear evidence of a jump from animals to humans similar to some zoonoses.
Despite ~45{,}000 papers, the precise mode of infection remains uncertain.
What is known:
- Not likely fecal-oral transmission.
- Not waterborne.
- Rarely foodborne.
- Early beliefs about transmission via communal eating are not supported by solid evidence.
- Oral-oral transmission is not a proven route due to bacteria not usually being viable in the mouth.
- Transmission from animals to humans is not established.
Acquisition tends to occur in early childhood within families; strongest link is mother-to-child contact. Hypotheses include gastro-oral routes (e.g., a mother pre-chewing the baby's food), but these are not definitively proven.
Once acquired, infection persists for life; there is only a tiny amount of adult-acquisition detectable in some studies.

Most infection is acquired in early childhood and persists lifelong.
Age acts as a marker of birth-cohort socioeconomic status: older individuals are often from eras with lower SES, contributing to higher observed prevalence in older cohorts (cohort effect).
The decline in prevalence in developed countries is explained by cohort effects plus improvements in hygiene and sanitation, not solely by treatment of existing cases.
Example: in Australia, prevalence is lower among Australian-born individuals compared with those born in higher-risk places, and among Australian-born, prevalence stratifies by location (surrogate for SES).
Global example: Singapore progressed from a two-generation earlier development stage to a front-running first-world status, and HP prevalence has plummeted accordingly.
In older cohorts, higher prevalence persists due to historical SES; as those cohorts die off and younger cohorts with higher childhood SES become predominant, population prevalence falls.
In clinical terms, primary-care treatment or specialist treatment reduces ulcers and cancer risk for treated individuals but has limited impact on overall population prevalence because the cohort effect and improvements in living conditions drive the trend.

Reported risk factors (not causes):
- Growing up sharing a bedroom with other siblings.
- Parents in lower socioeconomic income brackets.
- Absence of an indoor flush toilet.
- Absence of hot water.
All of these factors are tied to socioeconomic status; across populations, the risk of infection is inversely related to childhood SES:
- $\text{Risk} \propto \frac{1}{\text{SES}_{\text{childhood}}}$
Important principle: childhood SES determines risk; even if an individual later moves to a higher-SES environment, their early-life risk persists.
Migration effects: higher risk among people born in high-risk countries, and the children of those migrants still carry elevated risk due to intra-familial spread and birthplace-associated factors.
Indigenous groups in some settings show higher prevalence, often reflecting older age cohorts and lower childhood SES; familial clustering increases spread but transmission is not inevitable.

Within-country and within-city variation is common; not all populations are uniform.
Australia: three Sydney areas studied to reflect diverse SES and migration backgrounds:
- Hornsby: mostly Australian-born, high SES.
- Southwest Sydney: >60% overseas-born, lower SES.
- Concord Hospital area: mixed SES.
Findings from the Sydney study:
- Among Australian-born individuals, lower HP prevalence is associated with higher SES, consistent with the SES gradient.
- Among overseas-born residents, HP prevalence aligns with birthplace risk factors, indicating persistence of origin-associated risk.
- Higher HP prevalence in a population correlates with higher peptic ulcer rates.
Other global patterns:
- Sierra Leone: HP prevalence almost ubiquitous in children due to very low childhood SES.
- China: prevalence is patchy, reflecting regional developmental and SES differences.
- Singapore: a two-generation modernization led to a dramatic decline in HP prevalence.
Migrants and their children tend to have higher risk than native-born residents, due to lineage from higher-risk regions and intra-familial transmission.
Indigenous groups often exhibit higher prevalence, with older age cohorts driving higher prevalence; not universal but common in settings with lower childhood SES.

Eradication efforts in primary care or referrals reduce ulcer recurrence and cancer risk for treated individuals but have limited impact on overall population prevalence.
Public health impact comes from shifting birth cohorts toward higher SES and improving childhood living conditions (housing, sanitation, water supply).
Local control strategies should consider birthplace and childhood SES to target high-risk groups and adapt screening/education resources.
Population-level surveillance should account for migration patterns and SES-driven cohorts to plan resource allocation effectively.

Migrants and children of migrants: higher risk relative to non-migrants; risk is shaped by birthplace of parents and intra-familial transmission.
Indigenous populations: higher prevalence in some settings; older cohorts with lower childhood SES contribute disproportionately; transmission is familial but not guaranteed.

H. pylori prevalence varies globally and is strongly shaped by childhood SES and living conditions.
Infection is typically acquired in early childhood within families and persists for life; adult acquisition is uncommon.
The precise transmission pathway remains uncertain, with strong evidence against fecal-oral, waterborne, and frequent foodborne routes; intra-familial and early-life contact likely dominate.
Prevalence declines in the developed world due to cohort effects and improvements in hygiene and sanitation, compounded by migration patterns and SES shifts.
High-risk groups include migrants from high-prevalence regions and Indigenous populations in some areas; disease burden includes ulcers and cancer risk, but population-level declines are driven by social and environmental changes rather than treatment alone.