Changing trends in intestinal parasitic infections among long-term-residents and settled immigrants in Qatar

Abstract

Background: The rapid socio-economic development in Qatar in the last two decades has encouraged a mass influx of immigrant workers, the majority of whom originate from countries with low socio-economic levels, inadequate medical care and many are known to carry patent intestinal helminth and protozoan infections on arrival in Qatar. Some eventually acquire residency status but little is known about whether they continue to harbour infections.

Methods: We examined 9208 hospital records of stool samples that had been analysed for the presence of intestinal helminth and protozoan ova/cysts, over the period 2005-2008, of subjects from 28 nationalities, but resident in Qatar and therefore not recent arrivals in the country.

Results: Overall 10.2% of subjects were infected with at least one species, 2.6% with helminths and 8.0% with protozoan species. Although hookworms, Ascaris lumbricoides, Trichuris trichiura and Hymenolepis nana were observed, the majority of helminth infections (69%) were caused by hookworms, and these were largely aggregated among 20.0-39.9 year-old male subjects from Nepal. The remaining cases of helminth infection were mostly among Asian immigrants. Protozoan infections were more uniformly spread across immigrants from different regions when prevalence was calculated on combined data, but this disguised three quite contrasting underlying patterns for 3 taxa of intestinal protozoa. Blastocystis hominis, Giardia duodenalis and non-pathogenic amoebae were all acquired in childhood, but whereas prevalence of B. hominis rose to a plateau and then even further among the elderly, prevalence of G. duodenalis fell markedly in children aged 10 and older, and stayed low (< 2%) gradually falling even further in the elderly. In contrast the prevalence of non-pathogenic amoebae (Entamoeba coli, E. hartmanni, Endolimax nana and Iodamoeba buetschlii) peaked in the 30.0-39.9 age group and only then dropped to very low values among the oldest subjects examined. A worrying trend in respect of both helminth and protozoan parasites was the increase in prevalence over the period 2005-2008, in helminth infections prevalence increasing 2-3 fold by 2008, and in protozoan infections by 1.5-2.0 fold.

Conclusions: We suggest that helminth infections are probably acquired abroad when immigrants visit their home villages, whilst protozoan infections are reinforced by transmission in Qatar, possibly in the poorer areas of the state where immigrant workers live. We discuss the significance of these findings and emphasize that they have clear implications for the health authorities.

Figure 1

Factors affecting the prevalence of all parasitic infections combined. The significant terms in the minimum sufficient model are illustrated in (A-C) and the statistical significance is presented in the text. The model also included two expressions which did not encompass presence/absence of parasites and these are not given. For the goodness of fit of the minimum sufficient model, the likelihood ratio χ²₇₈₆ = 746.5 (P = 0.84). A. Changes in prevalence by age class and year of study. The number of subjects in each age class varied from 22 - 402 and see Table 1 for further details. The 95% confidence limits are only shown on two data-sets to give an idea of the range and to avoid obscuring the data. B. Effect of sex on prevalence across the 4 regions from which immigrant workers originated and native Qataris. The number of subject in each group was as follows from left to right for females = 500, 271, 833, 396, 1881 and for males 799, 240, 2381, 478, 1429. C. Prevalence of infection in both sexes by age class. The number of subjects in each age class varied from 53 - 516 among females and from 60 - 861 among males.

Figure 2

Prevalence of all protozoan infections combined. For the goodness of fit of the minimum sufficient model, the likelihood ratio χ²₈₃₄ = 804.3 (P = 0.76). Pen. = Peninsula and Med. = Mediterranean. A. Prevalence by the age classes in the population. For numbers of subject in each age class see Table 1B. Variation in prevalence in male and female subjects across the 5 regions in the study. For numbers of subjects in each subset see legend to Figure 1B.

Figure 3

Variation in prevalence of protozoan infections by age of host. For numbers of subject in each age class see Table 1, and the statistical analysis of the individual components of the final model is given in the text. A. B. hominis. For the goodness of fit of the minimum sufficient model, the likelihood ratio χ²₈₃₄ = 751.9 (P = 0.98). B. G. duodenalis. For the goodness of fit of the minimum sufficient model, the likelihood ratio χ²₈₄₂ = 621.8 (P = 1). C. Non-pathogenic amoebae. For the goodness of fit of the minimum sufficient model, the likelihood ratio χ²₇₉₂ = 577.3 (P = 1).

Figure 4

Variation in prevalence of protozoan infections by region of origin of subjects. For numbers of subject in each region see Table 1, and the statistical analysis of the individual components of the final model is given in the text. A. G. duodenalis. For the goodness of fit of the minimum sufficient model see legend to Fig. 3B. B. Non-pathogenic amoebae. For the goodness of fit of the minimum sufficient model see legend to Fig. 3C. C. Pathogenic amoebae. For the goodness of fit of the minimum sufficient model, the likelihood ratio χ²₈₄₂ = 411.7 (P = 1).