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November 12, 2022
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Unexplained persistent eosinophilia may be triggered by parasitic infection

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LOUISVILLE, Ky. — Parasitic infections commonly were the cause of unexplained persistent eosinophilia among inner-city patients, according to study results presented at the American College of Allergy, Asthma & Immunology Annual Meeting.

Eosinophilia is not an uncommon finding among patients seen at allergy clinics, Prudhvi Regula, MD, allergy and immunology fellow at Montefiore Health System, told Healio.

Source: Adobe Stock.
Patients presenting with persistent eosinophilia should undergo adequate evaluation for underlying causes. Source: Adobe Stock.

“It is a manifestation of an underlying medical problem,” he said. “There are several causes for eosinophilia. Previous studies have shown that patients with persistent eosinophilia are often not adequately evaluated for possible underlying causes. So, we did a prospective study to evaluate persistent blood eosinophilia for underlying causes in patients seen at our inner-city allergy clinic.”

Prudhvi Regula, MD
Prudhvi Regula

Researchers evaluated data of 82 patients (mean age, 50 years; range, 15-97; 70% female), of whom 42% were Hispanic, 37.5% Black and 10.9% white, which was representative of the Bronx population, Regula said during his presentation.

All patients had unexplained persistent peripheral blood eosinophilia, defined as an absolute eosinophile count (AEC) of higher than 500 cell/mL, on at least two occasions, with 17% of patients having hypereosinophilia, or an AEC of higher than 1,500 cells/mL.

Patients presented with comorbid allergic rhinitis (80.4%), asthma (53.6%), nasal polyposis (12%) and eczema (8.5%).

Patients underwent a detailed history; physical exam; chest X-ray; testing for IgE, tryptase and inflammatory markers; and parasitic workup, with further workup done for patients with markedly high eosinophilia and for those whom initial tests did not show clear etiology.

Overall, 24 patients, or 30% of the study population, tested positive for a parasitic infection, including Toxocara canis (25.3%), Strongyloides stercoralis (10.9%) — including four patients (6%) with both of these infections — Blastocystis hominis (4%), and one patient each with Wuchereria bancrofti and Schistosoma mansoni.

That almost one-third of patients presented with a parasitic infection was surprising, Regula told Healio.

“In the United States, parasitic infections are thought to be uncommon,” he said. “So when evaluating patients with eosinophilia, parasitic infection is not usually suspected as a cause unless there is a travel history to developing counties. Several patients in our study who tested positive for parasitic infections did not have a travel history to developing countries.”

Seventeen patients went on to receive antiparasitic treatment and were followed up at least 4 weeks following treatment. All 12 of those who had post-treatment AEC available showed significant reductions following treatment, whereas the untreated patients continued to have persistent eosinophilia, which in some cases continued to increase.

Of the six patients who did not receive treatment, two had a parasitic infection for which treatment is not commercially available in the U.S., and four were denied coverage for treatment by their insurance providers.

Additionally, researchers found that 23% of the population had elevated IgG4, although they did not have evidence of IgG4-related disease. Also, five patients (9%) had elevated IL-5 levels, four of whom also had parasitic infections. Researchers plan to expand the study population to further assess the association between IL-5 levels and eosinophilia, Regula told Healio.

Ultimately, these results show that patients presenting with persistent eosinophilia should undergo adequate evaluation for underlying causes, he added.

“While evaluating these patients, workup for appropriate parasitic infection should be considered even if patients do not have a travel history to developing countries,” he said.