Natural History of Cryptosporidiosis in a Longitudinal Study of Slum-Dwelling Bangladeshi Children: Association with Severe Malnutrition

Abstract

Background: Cryptosporidiosis is a common cause of infectious diarrhea in young children worldwide, and is a significant contributor to under-five mortality. Current treatment options are limited in young children. In this study, we describe the natural history of Cryptosporidium spp. infection in a birth cohort of children in Bangladesh and evaluate for association with malnutrition.

Methodology/principal findings: This is a longitudinal birth cohort study of 392 slum-dwelling Bangladeshi children followed over the first two years of life from 2008 to 2014. Children were monitored for diarrheal disease, and stool was tested for intestinal protozoa. Anthropometric measurements were taken at 3-month intervals. A subset of Cryptosporidium positive stools were genotyped for species and revealed that C. hominis was isolated from over 90% of samples. In the first two years of life, 77% of children experienced at least one infection with Cryptosporidium spp. Non-diarrheal infection (67%) was more common than diarrheal infection (6.3%) although 27% of children had both types of infection. Extreme poverty was associated with higher rates of infection (chi-square, 49.7% vs 33.3%, p = 0.006). Malnutrition was common in this cohort, 56% of children had stunted growth by age two. Children with Cryptosporidium spp. infection had a greater than 2-fold increased risk of severe stunting at age two compared to uninfected children (odds ratio 2.69, 95% CI 1.17, 6.15, p = 0.019) independent of sex, income, maternal body-mass index, maternal education and weight for age adjusted z (WAZ) score at birth.

Conclusions/significance: Cryptosporidium infection is common (77%) in this cohort of slum-dwelling Bangladeshi children, and both non-diarrheal and diarrheal infections are significantly associated with a child's growth at 2 years of age.

Fig 1. Total number of diarrheal episodes per month.

The x-axis represents the child’s age in months, and the y-axis represents total number of diarrheal episodes per age-month. The dark blue segment represents number of total diarrheal episodes, and the light blue segment represents the proportion of diarrheal episodes per month that test positive for Cryptosporidium species. In each month, the total possible number of children included is 392. Cryptosporidium infection makes up a very small portion of the total burden of diarrhea in our cohort.

Fig 2. Total number of children with Cryptosporidium infection per month.

The x-axis represents age of the child in months, and the y-axis represents total number of infected children per age-month. The solid-segment represents number of children with asymptomatic Cryptosporidium infection, and the lined-segment represents number of children with diarrhea from Cryptosporidium infection. In each month, the total possible number of children included is 392. A child who had both a diarrheal and asymptomatic stool positive in the same month was counted as having Cryptosporidium diarrhea. This figure demonstrates peaks of diarrheal Cryptosporidium infection at 10 and 17 months of age, and peaks of asymptomatic infection at 10–13 and 17 months of age.

Fig 3. Box plot of mean height-for-age adjusted z-scores over first 24 months of life.

In this cohort of 392 children, mean HAZ dropped continuously over the first two years of life, which was also consistently well below the W.H.O. reference population mean (indicated by red line).

Fig 4. Kaplan Meier curve of the 302 children infected with Cryptosporidium spp. categorized by type of infection experienced (diarrheal, non-diarrheal, or both).

There was no significant difference between timing of first asymptomatic versus symptomatic Cryptosporidium infection (HR 0.68, 95% CI 0.42, 1.09, p = 0.11). However, children who went on to develop both symptomatic and asymptomatic infection did get infected earlier in life (HR = 1.74, 95% CI 1.34, 2.27, p < 0.0001).

Fig 5. Phylogenetic Relationship of 101 Cryptosporidium parasites isolated in Bangladesh to each other (open circle) and to the reference sequences (closed circle) gp60Ia (HQ631408), gp60Ib (AY738187), gp60Id (AY738192), gp60Ie (AY738184), gp60If (AF440638).

Neighbor-Joining consensus tree was drawn using the Geneious program (R7). Any apparent diversity is due to ambiguous bases.