Few studies have explored the possible correlation between the concentration of ragweed pollen and the severity of both rhino-conjunctivitis and asthma. To explore this knowledge gap, biologist Maira Bonini and colleagues conducted a study based out of the North-West Metropolitan area bordering the city of Milan, known for its high ragweed infestation.

“Ragweed (Ambrosia artemisiifolia) is an invasive plant with highly allergenic pollen that causes seasonal respiratory allergy in people around the world,” Bonini says. “Because of the high prevalence of ragweed allergy in the North-West Milan area, it is important to attain sufficient control of rhino-conjunctivitis and asthma symptoms, as well as to reduce the social and psychological consequences of the allergy during the ragweed season.”

She adds that calculating a threshold for symptom pollen levels is a key tool for developing ragweed-allergy preventative measures.

Study Focused on Conjunctivitis, Rhinitis, and Asthma Symptoms

The study, published in Scientific Reports, consisted of 66 participants separated into two groups. One group included individuals who have never received ragweed allergen immunotherapy (AIT; no AIT group, N=42). The second group received treatment with ragweed AIT (AIT treated group, N=24).

Both pollen counts and daily symptom/medication patient diaries were tracked between July 16, 2014, and September 15, 2014, considered the peak blooming time for ragweed in the area. The study team focused on three symptom categories: conjunctivitis, rhinitis, and asthma.

A significant correlation was identified between pollen load and the intensity of the three symptoms monitored both in the no AIT group (τ = 0.341, 0.352, and 0.721, respectively; ρ=0.48, 0.432, and 0.881, respectively; P value, <0.001) and in the AIT treated group (τ = 0.46, 0.610, and 0.66, respectively; ρ=0.692, 0.805, and 0.824, respectively; P value, <0.001). In both groups, Bonini and colleagues observed a positive correlation between the number of symptoms reported and medication use.

A moderate to strong positive correlation with a high statistical implication between the number of symptoms and drug consumption was not observed in any of the AIT patients. There was robust evidence of a positive monotonic association between the two variables in the analysis (Table). In AIT-treated patients, this relationship was more moderate but still notable.

Strong Link Found Between Number of Symptoms and Drug Intake

According to Bonini, the key findings of the study include:

  • There is a strong relationship between ragweed pollen concentration and ocular, nasal, and other respiratory symptom severity in ragweed allergy patients;
  • There is a strong correlation between the number of symptoms and medication use;
  • The defining of specific health thresholds for airborne ragweed pollen can represent an important tool for setting ragweed-allergy preventive measures; and
  • The ragweed AIT can reduce the symptoms caused by exposure to ragweed pollen.

Given these findings, Bonini and colleagues hope that further research on this topic is pursued. “Since our sample was relatively small, our findings may need to be validated in the same region and with a larger population,” she says.

Clinicians, Bonini adds, would benefit from knowing what the ragweed pollen symptom thresholds are, as they are a useful prevention tool and an indicative reference for planning various territorial interventions with the aim of reducing exposure to ragweed.

“Moreover, [practitioners] would benefit from knowing that treatment with AIT is effective in reducing the severity of ragweed allergy symptoms with particular regard to asthma,” she notes.