Any physician with patients who travel worldwide will occasionally be faced with the clinical problem of unexplained eosinophilia. Schulte and colleagues describe their findings in a retrospective analysis of 14,298 patients who were examined at a tropical medicine clinic in Germany after travel to developing countries.

Eosinophilia, defined as at least 8 percent eosinophils in a white blood cell (WBC) count, was present in 4.8 percent of travel subjects overall. The risk for eosinophilia was highest in those returning from western and southern Africa. Those traveling to the Indian subcontinent, southeast Asia, and Latin America had the lowest incidence of increased eosinophils.

The most common symptoms encountered in patients with eosinophilia were fatigue, diarrhea, or skin lesions suspicious for parasitic infection. However, one third of the patients were asymptomatic. Using a variety of stool, urine, serologic, and skin biopsy tests, a definitive diagnosis for the eosinophilia was made in 36 percent of patients. The probability of a definitive diagnosis was greater than 60 percent in patients with higher levels of eosinophils (16 percent of WBC count).

The most common category of infection, especially in those with higher eosinophil counts, was helminthic infection. Schistosomiasis and hookworm infection were the most common entities in this group. Protozoal infection was the next most common category, with about one half of cases caused by amoebiasis.

The variety of parasites encountered was quite broad, with more than 30 different pathogens listed among the definitive diagnoses. As noted, most patients could not be given a certain diagnosis, and the authors further noted that the majority of those with documented helminthic infection did not demonstrate eosinophilia.

The authors concluded that the diagnostic significance of blood eosinophilia is limited. Travel to western and central Africa was associated with a higher incidence of eosinophilia, and patients with the highest eosinophil counts were the most likely to have a definitive diagnosis after clinical work-up.