Conceptual framework of the quantitative microbial risk assessment model.

<p>Framework includes the computational process, parameters, and variables included in estimating risk of infection for <i>Cryptosporidium</i> or for <i>Giardia</i> from contaminated drinking water. The driving input parameter (raw concentration of parasites) is identified at the left most section of the figure. Boxes represent modeled variables (e.g., modified concentration and load of parasites), ovals represent exogenous parameters and assumptions affecting modeled variables (e.g. HUM, MST, and ENV scenarios represent the fraction of parasites belonging to a species infectious-to-humans), and the dashed box on the right represents the model output. Units are displayed within brackets under each description. Variable and parameter symbols shown directly above their respective variable or parameter are used in Eq <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0006231#pntd.0006231.e003" target="_blank">1</a>, <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0006231#pntd.0006231.e004" target="_blank">2</a> and <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0006231#pntd.0006231.e012" target="_blank">4</a>.</p

Animal host mean prevalence rates (<i>Z</i>_<i>i</i>) of shedding zoonotic species infectious-to-humans (i.e., <i>C</i>. <i>parvum</i> or <i>G</i>. <i>lamblia</i> assemblage A or B) estimated from published literature and used in Eq 3 to calculate the overall zoonotic fraction ( in Table 1) of <i>Cryptosporidium</i> and <i>Giardia</i> parasites shed by animals in Puri District able to infect humans.

<p>Animal host mean prevalence rates (<i>Z</i>_<i>i</i>) of shedding zoonotic species infectious-to-humans (i.e., <i>C</i>. <i>parvum</i> or <i>G</i>. <i>lamblia</i> assemblage A or B) estimated from published literature and used in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0006231#pntd.0006231.e010" target="_blank">Eq 3</a> to calculate the overall zoonotic fraction ( in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0006231#pntd.0006231.t001" target="_blank">Table 1</a>) of <i>Cryptosporidium</i> and <i>Giardia</i> parasites shed by animals in Puri District able to infect humans.</p

Fraction of the observed 7-day recall child diarrhea period prevalence in the Odisha Sanitation Trial (12% in 2012 and 9% in 2013) estimated to be attributable to drinking tubewell water contaminated with <i>Cryptosporidium</i> and <i>Giardia</i> under different human pathogenicity scenarios examined (median % and interquartile range (IQR)).

<p>Fraction of the observed 7-day recall child diarrhea period prevalence in the Odisha Sanitation Trial (12% in 2012 and 9% in 2013) estimated to be attributable to drinking tubewell water contaminated with <i>Cryptosporidium</i> and <i>Giardia</i> under different human pathogenicity scenarios examined (median % and interquartile range (IQR)).</p

Main parameters used in the quantitative microbial risk assessment and susceptible-infected-recovered models developed to simulate waterborne diarrheal infections in children < 5 in Puri District due to <i>Cryptosporidium</i> and <i>Giardia</i> in drinking water from deep (DTW) and shallow (STW) tubewells over two monsoon seasons.

<p>Main parameters used in the quantitative microbial risk assessment and susceptible-infected-recovered models developed to simulate waterborne diarrheal infections in children < 5 in Puri District due to <i>Cryptosporidium</i> and <i>Giardia</i> in drinking water from deep (DTW) and shallow (STW) tubewells over two monsoon seasons.</p

Concentrations of <i>Cryptosporidium</i> oocysts and <i>Giardia</i> cysts detected in tubewells during the 2012 and 2013 monsoon season.

<p>Concentrations of <i>Cryptosporidium</i> oocysts and <i>Giardia</i> cysts detected in tubewells during the 2012 and 2013 monsoon season.</p

Boxplots of daily risk of <i>Cryptosporidium</i> and <i>Giardia</i> infection.

<p>Daily risk is for an individual child drinking deep and shallow tubewell water in 2012 (A & B) and 2013 (C & D), accounting for boiling rates (9% and 16% by deep and shallow tubewell users respectively), under different scenarios representing the fraction of parasites infectious-to-humans (HUM = H, MST = M, ENV = E). US EPA tolerable daily risk of infection from drinking water is denoted with the dashed line at log₁₀ (0.0001%).</p

Estimating <i>Cryptosporidium</i> and <i>Giardia</i> disease burdens for children drinking untreated groundwater in a rural population in India

<div><p>Background</p><p>In many low-income settings, despite improvements in sanitation and hygiene, groundwater sources used for drinking may be contaminated with enteric pathogens such as <i>Cryptosporidium</i> and <i>Giardia</i>, which remain important causes of childhood morbidity. In this study, we examined the contribution of diarrhea caused by <i>Cryptosporidium</i> and <i>Giardia</i> found in groundwater sources used for drinking to the total burden of diarrheal disease among children < 5 in rural India.</p><p>Methodology/Principal findings</p><p>We studied a population of 3,385 children < 5 years of age in 100 communities of Puri District, Odisha, India. We developed a coupled quantitative microbial risk assessment (QMRA) and susceptible-infected-recovered (SIR) population model based on observed levels of <i>Cryptosporidium</i> and <i>Giardia</i> in improved groundwater sources used for drinking and compared the QMRA-SIR estimates with independently measured all-cause (i.e., all fecal-oral enteric pathogens and exposure pathways) child diarrhea prevalence rates observed in the study population during two monsoon seasons (2012 and 2013). We used site specific and regional studies to inform assumptions about the human pathogenicity of the <i>Cryptosporidium</i> and <i>Giardia</i> species present in local groundwater. In all three human pathogenicity scenarios evaluated, the mean daily risk of <i>Cryptosporidium</i> or <i>Giardia</i> infection (0.06–1.53%), far exceeded the tolerable daily risk of infection from drinking water in the US (< 0.0001%). Depending on which protozoa species were present, median estimates of daily child diarrhea prevalence due to either <i>Cryptosporidium</i> or <i>Giardia</i> infection from drinking water was as high as 6.5% or as low as < 1% and accounted for at least 2.9% and as much as 65.8% of the all-cause diarrhea disease burden measured in children < 5 during the study period. <i>Cryptosporidium</i> tended to account for a greater share of estimated waterborne protozoa infections causing diarrhea than did <i>Giardia</i>. Diarrhea prevalence estimates for waterborne <i>Cryptosporidium</i> infection appeared to be most sensitive to assumptions about the probability of infection from ingesting a single parasite (i.e. the rate parameter in dose-response model), while <i>Giardia</i> infection was most sensitive to assumptions about the viability of parasites detected in groundwater samples.</p><p>Conclusions/Significance</p><p>Protozoa in groundwater drinking sources in rural India, even at low concentrations, especially for <i>Cryptosporidium</i>, may account for a significant portion of child diarrhea morbidity in settings were tubewells are used for drinking water and should be more systematically monitored. Preventing diarrheal disease burdens in Puri District and similar settings will benefit from ensuring water is microbiologically safe for consumption and consistent and effective household water treatment is practiced.</p></div

Boxplots of simulated diarrhea daily point prevalence (% of children).

<p>Prevalence is shown for the study population during the 90-day monsoon season estimated from 1,000 simulations of the quantitative microbial risk assessment and susceptible-infected-recovered models. Results shown for deep (DTW) and shallow (STW) tubewell users (either infection), and for <i>Cryptosporidium</i> (<i>Crypto</i>.) and <i>Giardia</i> (<i>Gia</i>.) infections (either tubewell type) for the monsoon season in 2012 and 2013, under different scenarios used to assign the fraction of parasites infectious-to-humans (HUM = H: orange, MST = M: green, ENV = E: blue). Combined DTW & STW results are for an average child in a tubewell using household, accounting for rates of deep (48%) and shallow (52%) tubewell usage in the study population. Boiling rates (9% and 16% for deep and shallow tubewell users respectively) are accounted for in all results. Different vertical scales for 2012 and 2013 plots highlight the upper limits of burden between years.</p

Key causes of concern about space for replacing pit latrines.

<p>Key causes of concern about space for replacing pit latrines.</p

Likelihood of selecting ecological sanitation over pit latrines when there is concern about space for pit latrines (n = 1198).

<p>Likelihood of selecting ecological sanitation over pit latrines when there is concern about space for pit latrines (n = 1198).</p