Case-Control Study of Cryptosporidium Transmission in Bangladeshi Households

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.

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.

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.

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.