Approximately 21% of the world's population is exposed to stable malaria due to Plasmodium falciparum [1], and an estimated 740 million individuals are infected with hookworms (Necator americanus and Ancylostoma duodenale) [2]. A common complication of P. falciparum malaria is anemia, particularly among children and pregnant women [3–5], whereas hookworm infection results in intestinal blood loss and is probably second only to malaria as an infectious cause of anemia [6]. The widespread occurrence and congruent spatial extents of Plasmodium species and hookworm infections make coinfection common, especially in sub-Saharan Africa: for example, an estimated 45 million school-aged children are at risk of coinfection [7]. Despite this ubiquity of coinfection and its potential consequences for public health, we know little about epidemiology of malaria-hookworm coinfection. Previous studies have suggested that infection with 1 species may exacerbate infection and disease related to the other [8, 9]. Furthermore, the distinct mechanisms by which Plasmodium species and hookworm infections cause anemia may enhance the risk of anemia and iron deficiency among individuals harboring both species [10–12]. If shown to be correct, these interactions have considerable implications for parasite control in the tropics. Yet there are few detailed epidemiological studies specifically addressing malaria-hookworm coinfection [13, 14], with most existing studies of malaria-helminth coinfection typically focusing on concomitant infection with Schistosoma species and other soil-transmitted helminths [15–18]. These studies have been either retrospective analyses of previously collected data, clinic based, or conducted among specific subgroups, and consequently they are subject to potential bias and confounding due to individual, household, and geographic factors. These features make the contradictory findings of negative, positive, and no associations reported in the literature difficult to interpret [19–21]. Recent studies in Ghana and Uganda do, however, suggest that among pregnant women coinfection with malaria and hookworm occurs more frequently than would be expected by chance after accounting for demographic and socioeconomic characteristics [13, 14]. We report results from a purposively designed, age-stratified study of the epidemiology of Plasmodium-hookworm coinfection in Uganda. The study aims to determine the patterns, risk factors, and hematological consequences of coinfection in a rural community where malaria and hookworm are endemic. We place emphasis on differences by age group and residential location, using a hierarchical, spatially explicit modeling approach.
