Case-Control Study of Cryptosporidium Transmission in Bangladeshi Households

Abstract

Background: Cryptosporidium is a leading contributor to diarrheal morbidity and mortality in under-5 children worldwide. As there is no vaccine and no effective drug therapy in young children for this infection, preventing infection is critical. We undertook a pilot case-control study to define the extent of person-to-person transmission of cryptosporidiosis within an urban and a rural community in Bangladesh.

Methods: We enrolled 48 case families with a Cryptosporidium-infected child aged 6-18 months. Controls were age- and sex-matched Cryptosporidium-negative children in 12 households. Children and household members were followed for 8 weeks with weekly illness survey and stool testing with quantitative polymerase chain reaction for Cryptosporidium.

Results: In the 24 urban case families, the secondary attack rate was 35.8% (19/53) vs 0% (0/11) in controls (P = .018, χ2 test). In contrast, in the 24 rural case families, the secondary attack rate was 7.8% (5/64) vs 0% (0/21) in controls (P = .19, χ2 test). Genotyping by gp60 demonstrated infection with the same subspecies in 5 families, and evidence of transmission in 2. Serologic response to Cryptosporidium infection was associated with younger age, longer duration of infection, and Cryptosporidium hominis gp60_IbA9G3R2 infection.

Conclusions: In the urban site, the high rate of secondary infection and infection with the same subspecies within families suggests that person-to-person transmission is a major source of Cryptosporidium infection for young children living in this region. Molecular genotyping can be applied to determine transmission of Cryptosporidium in endemic regions. Further work is needed to understand the differences in parasite transmissibility and immunity to different genotypes.

Keywords: Cryptosporidium hominis; Cryptosporidium meleagridis; Cryptosporidium parvum; diarrhea; transmission.

Figure 1.

Cryptosporidium genotypes detected in 20 Mirpur households over the 8-week follow-up period. A box shaded in color indicates that individual tested positive for Cryptosporidium in that week and the genotype was identified. An asterisk (*) indicates the subject had Cryptosporidium-positive diarrhea in that week, and an asterisk without color indicates positive Cryptosporidium detection without identification of genotype. In 6 families, household members were already infected with Cryptosporidium at baseline. Cryptosporidium hominis gp60_1aA18R3 was the most abundant genotype. Families 11 and 17 demonstrate transmission of a novel genotype from a brother and father to the index child. In individuals with multiple genotypes detected in 1 sample, the most abundant genotype is represented here.