A Decade of Data Reveals Rising Allergy Sensitization in Jordan

A decade’s worth of blood tests from nearly five thousand Jordanians has revealed a steady and troubling rise in allergic sensitization to airborne allergens, with olive pollen emerging as the country’s single most potent trigger. The findings, drawn from one of the largest immunological datasets ever assembled in the Middle East, offer a rare long-term window into how the immune systems of urban populations are responding to a changing environment—and they suggest that even the extraordinary lockdowns of the COVID-19 pandemic did nothing to slow the trend.

The study, published in Immunity, Inflammation and Disease, was conducted by researchers at Biolab Diagnostic Laboratories, a private laboratory network operating across Jordan. The team retrospectively analyzed serum samples from 4,675 patients tested between January 2012 and December 2022, spanning ten consecutive years and covering ten of Jordan’s twelve governorates. Because the vast majority of samples—93.5 percent—came from the capital, Amman, the dataset primarily reflects the sensitization profile of a highly urbanized population living at the crossroads of Mediterranean and desert climates, where pollen-laden winds and dust storms alike shape the airborne allergen landscape.

The biological phenomenon at the heart of the study is sensitization: the process by which the immune system, upon first encountering an inhaled allergen such as pollen or animal dander, produces allergen-specific immunoglobulin E (IgE) antibodies. These antibodies arm mast cells throughout the body, priming them to unleash inflammatory mediators like histamine upon any subsequent exposure. The result is the sneezing, wheezing, and airway inflammation that characterize allergic rhinitis and asthma—conditions that now affect more than 400 million and 300 million people worldwide, respectively. Tracking who is sensitized, and to what, is therefore a critical step in anticipating the future burden of allergic disease.

To measure sensitization, the researchers used a standardized enzyme allergosorbent test, a semi-quantitative immunoblot assay in which patient serum is incubated with a strip coated with 29 distinct aeroallergens. Bound IgE antibodies are detected with an enzyme-linked anti-human IgE reagent, producing a colorimetric signal that is scanned and classified into six ascending classes, from class 1 (the lowest detectable level, 0.35 kilounits per liter) to class 6 (100 kilounits per liter or more). The panel included grass, tree, grain, and weed pollens; dust mites; animal danders from cats, dogs, horses, and farm animals; molds such as Aspergillus fumigatus and Alternaria alternata; and cockroach. Samples positive for cross-reactive carbohydrate determinants—pan-allergen structures that frequently generate clinically meaningless IgE responses—were excluded, as were repeat tests, to avoid distorting the analysis.

The headline result is stark: 45.5 percent of the tested population carried IgE antibodies to at least one aeroallergen, and the prevalence climbed steadily across the decade, from 40 percent in 2012–2015 to 44.8 percent in 2016–2019 and 50.6 percent in 2020–2022. Multivariable logistic regression confirmed that the temporal trend held even after adjusting for sex and age, with patients tested in the earliest period showing significantly lower odds of sensitization than those tested during the pandemic years. Pollens, molds, and animal danders were the allergen groups driving the increase, while dust mites and cockroach sensitization remained comparatively stable.

Ranking the individual allergens produced a list that reads like a portrait of Jordan itself. Olive tree pollen topped the table, sensitizing 21.9 percent of IgE-positive individuals—a finding that tracks with the fact that olive trees cover roughly 72 percent of the country’s agricultural land. Late-blooming tree pollens followed at 19.1 percent, then cat dander at 17.5 percent, an intriguing result in a country where indoor cat ownership is relatively low. The authors point to a likely explanation: Jordan’s ubiquitous outdoor and stray cats shed allergens that hitchhike on clothing and in dust into homes and shared spaces. Grass pollens, grain pollens, and herb pollens filled out the upper ranks, while the two major dust mite species, Dermatophagoides pteronyssinus and D. farinae, ranked eleventh and twelfth. Cage birds, feathers, and the mold Cladosporium herbarum were the rarest sensitizers.

The demographic patterns were equally revealing. Males had 35 percent higher odds of sensitization than females, a sex bias consistent with international birth-cohort studies that have implicated genetic, hormonal, and lifestyle factors. Age produced a classic inverted-U curve: the 20-to-40-year group showed the highest prevalence at 51.8 percent, while both younger and older participants were significantly less likely to be sensitized. The decline after middle age is thought to reflect immunosenescence—the gradual weakening of immune responsiveness with age—while the lower rates in children may reflect the cumulative nature of sensitization, which builds through years of repeated exposure.

Perhaps the most surprising finding concerns the pandemic. Between 2020 and 2022, Jordan, like most of the world, imposed strict non-pharmaceutical interventions: mask mandates, movement restrictions, and lockdowns that dramatically altered how people interacted with the outdoors. Yet sensitization prevalence did not fall—it rose to its decade-high level. The pattern was mixed rather than purely indoor-focused: pollen sensitization increased alongside certain indoor allergens such as some animal danders and molds, while dust mites and cockroach held steady. The authors are careful to note the limits of interpretation. Because the study compared different individuals across successive time periods rather than following the same people longitudinally, the temporal increase cannot be causally attributed to pandemic behavior. Changes in healthcare-seeking patterns, testing practices, and other unmeasured factors may also have contributed. Still, the absence of any pandemic-era decline challenges the simple assumption that reduced outdoor exposure should translate into reduced sensitization, particularly since sensitization reflects cumulative immune memory rather than moment-to-moment exposure.

One subtle immunological detail emerged from the titer analysis. Several animal danders—hamster, dog, cow, horse, goat, and sheep—showed relatively low sensitization prevalence but disproportionately high IgE classes among those who were sensitized. The researchers suggest a likely mechanism: cross-reactivity. Mammalian dander allergens share homologous protein families, notably serum albumins and lipocalins. Cat serum albumin, known as Fel d 2, is structurally similar to albumins from dogs, horses, and cows, while the lipocalin Fel d 4 has counterparts across domestic and farm animals. IgE raised against cat allergens can therefore bind related proteins from species a person has rarely, if ever, encountered—producing measurable sensitization without direct exposure.

Beyond its scientific findings, the study carries practical weight. The authors propose allergen-aware urban planning—limiting the planting of highly allergenic olive trees in dense residential areas, publishing seasonal pollen forecasts, managing stray animal populations, and promoting standard dust mite controls such as humidity regulation and allergen-impermeable bedding. They also argue for expanding access to allergen immunotherapy through national protocols aligned with the country’s dominant sensitizers. The team acknowledges the limitations inherent in real-world laboratory data: the cohort was clinically enriched, meaning the 45.5 percent figure cannot be read as a population-wide prevalence, and detailed clinical information was unavailable. Yet the sheer scale, decade-long span, and single-platform consistency of the dataset make it the most detailed portrait of aeroallergen sensitization in Jordan to date—and a template for how routine diagnostic data, mined carefully, can illuminate the shifting immunological relationship between urban populations and the air they breathe.

Subject of Research: Long-term trends in aeroallergen-specific IgE sensitization in Jordan

Article Title: Trends in Aeroallergen IgE Sensitization in Jordan: A Decade‐Long Observational Study

Article References: Abu‐Kwaik, J., Rawashdeh, A., Saddedin, B., Ghunaim, M., Hasan, T., Abdelnour, A., & Abu‐Dayyeh, I. (2026). Trends in Aeroallergen IgE Sensitization in Jordan: A Decade‐Long Observational Study. Immunity, Inflammation and Disease, 14(10), Article e70533. https://doi.org/10.1002/iid3.70533

Image Credits: AI Generated

DOI: 10.1002/iid3.70533

Keywords: aeroallergens, IgE sensitization, olive pollen, allergic rhinitis, asthma, Jordan, COVID-19 pandemic, enzyme allergosorbent test, cat dander, dust mites, cross-reactivity, urbanization