Low incidence of helminth infections (schistosomiasis, strongyloidiasis, filariasis, toxocariasis) among Dutch long-term travelers: A prospective study, 2008-2011

BACKGROUND: Despite the considerable burden of helminth infections in developing countries and increasing international travel, little is known about the risks of infection for travelers. OBJECTIVE: We studied the attack and incidence rate of serology confirmed strongyloidiasis, filariasis, and toxocariasis among long-term travelers and associated factors. A second objective was to evaluate eosinophilia as a positive/negative predictive value (PPV/NPV) for a recent helminth infection. METHODS: From 2008 to 2011, clients of the Public Health Service travel clinic planning travel to (sub)tropical countries for 12–52 weeks were invited to participate in a prospective study. Participants kept a weekly diary, recording itinerary, symptoms, and physician visits during travel and completed a post-travel questionnaire. Pre- and post-travel blood samples were serologically tested for the presence of IgG antibodies against Schistosoma species, Strongyloides stercoralis, filarial species, and Toxacara species and were used for a blood cell count. Factors associated with recent infection were analyzed using Poisson regression. Differences among groups of travelers were studied using chi square tests. RESULTS: For the 604 participants, median age was 25 years (interquartile range [IQR]: 23–29), 36% were male, median travel duration was 20 weeks (IQR: 15–25), and travel purpose was predominantly tourism (62%). Destinations were Asia (45%), Africa (18%), and the Americas (37%). Evidence of previous infection was found in 13/604 participants: antibodies against Schistosoma spp. in 5 (0.8%), against S.stercoralis in 3 (0.5%), against filarial species in 4 (0.7%), and against Toxocara spp. in 1 (0.2%). Ten recent infections were found in 9 participants (3, 1, 6, 0 cases, in the above order), making the attack rates 0.61, 0.17, 1.1 and 0, and the incidence rates per 1000 person-months 1.5, 0.34, 2.6 and 0. The overall PPV and NPV of eosinophila for recent infection were 0 and 98%, respectively. CONCLUSIONS: The risk of the helminth infections under study in this cohort of long-term travelers was low. Routine screening for eosinophilia appeared not to be of diagnostic value.