In a recent study published in the Emerging Infectious Diseases Journal, researchers used comprehensive public health data and advanced statistical models to provide an evidence-based estimation of global and regional human Brucellosis incidence.
Study: Global Estimate of Human Brucellosis Incidence. Image Credit: Kateryna Kon/Shutterstock.com
Brucellosis is a bacterial disease impacting livestock and humans globally, with the most virulent Brucella species being B. abortus in cattle, B. melitensis in sheep and goats, and B. suis in swine.
While these infections pose risks to livestock and are zoonotic, human brucellosis is less recognized, and symptoms in humans resemble influenza, with chronic cases causing arthritis, myocarditis, and neuropathies.
Humans acquire the disease from unpasteurized milk or handling infected tissues, livestock owners, consumers of raw milk products, abattoir workers, and veterinarians at high risk. Despite its global recognition, the annual incidence of Brucellosis remains uncertain due to inconclusive prior studies.
About the study
To estimate the annual incidence of human brucellosis, the present study combined open-source data from the World Organization of Animal Health (WOAH) and the World Bank, using three statistical models.
These models drew from weighted average interpolation, bootstrap resampling, and Bayesian hierarchical structures. By defining population risk as the ratio of new cases to the total at-risk population, they formed a basic framework for their models. The research used data from 2014-2018, adhering to the Guidelines for Accurate and Transparent Health Estimates Reporting (GATHER).
The researchers stratified global populations into country and region groups, integrating World Bank population estimates from the chosen years. Countries were grouped into continental regions (Africa, Americas, Asia, Europe).
Oceania was excluded due to insufficient data. They also categorized country reports based on their informativeness. For countries reporting more than three out of five years, the average reported case count (RCC) was used.
Using observed RCCs, they estimated case counts for non-reporting countries and determined the incidence by dividing RCCs by the at-risk population. A key risk factor for brucellosis is contact with infected livestock, with the risk primarily hinging on the frequency of contact between infectious livestock/products and humans, especially on small farms in rural areas.
By leveraging the World Bank's data, they pinpointed rural populations to determine each country's at-risk populace, subsequently categorizing them based on the presence or absence of reported brucellosis cases.
While previous research suggested that determining an accurate global disease incidence using only human data was unachievable, this study adopted a novel approach. Researchers used human and animal data to estimate the global and regional risk and incidence of human brucellosis.
The WOAH's annual reports between 2014 and 2018 were analyzed. They revealed that 83.1% of the livestock brucellosis data, covering the three major Brucella species, was available, as opposed to 48.4% of human data.
On a regional breakdown, Europe provided the highest percentage of reports at 97.5%, followed by Asia, the Americas, and Africa. Livestock data, being more comprehensive than human data, was the foundational base for estimating disease incidence. Despite this, gaps in data regarding specific Brucella species were evident.
Of the global populace, 82.3% of countries and 43.2% of individuals were deemed at risk. Regionally, Africa had the highest percentage of countries and populations at risk, followed by Asia, the Americas, and Europe. The study had to exclude some countries from Oceania due to inadequate reporting.
Identifying populations vulnerable to brucellosis was essential for disease control. Risk levels for different populations were calculated based on country reports of human cases. Heat maps were then produced, highlighting the global average risk as approximately 500 new cases per 1 million at-risk individuals.
Three models were used post risk assessment to deduce annual incidence. All models' results agreed that the global annual incidence of human brucellosis was much higher than past estimations.
With Asia and Africa accounting for most cases, discrepancies between models were mainly in data representation. The researchers cross-checked their models against data from Europe, a region known for comprehensive reporting, confirming the validity of their models.
Heat maps were generated using incidence and at-risk population data to depict regional risks visually. All studied regions exhibited some disease risk; Africa, especially its equatorial regions, presented the highest risk. In Asia, the principal risk was in the Middle East, whereas Central America emerged as the primary hotspot in the Americas.
Despite Europe having the lowest risk overall, there was significant concern in the Eastern Mediterranean area.
Although the true annual incidence of human brucellosis remains elusive, the authors have compiled an evidence-based, scientifically computed estimate.
The present study reveals that the contemporary disease risk conditions most likely translate to an approximate global annual incidence that was many times higher than previously suggested.
Moreover, the risk of acquiring the disease was highest within resource-limited regions. Further, research must be conducted to understand the role of misdiagnosis and underdiagnosis of human brucellosis, as those factors will undoubtedly amplify case estimates and risk profiles within those regions.