Ph.D. Thesis Defense Announcement

Estimating the Health Risks Posed by Intermittent Water Supply Using Quantitative Microbial Risk Assessment

By

Aaron Bivins, P.E.

Advisor:

Dr. Joe Brown (CEE)

Committee Members:

Dr. Kostas Kostantinidis (CEE), Dr. Anjali Bohlken (INTA), Dr. Heather Murphy (Temple University), Dr. Mark Borchardt (USDA Agriculture Research Service)

Date & Time: Thursday, October 24th, at 10:00 am

Location: Sustainable Education Building (SEB), Room 122

ABSTRACT
Intermittent water supply (IWS) is a prevalent deficiency in piped-on-premise water supplies. In many settings
water distribution systems are intentionally pressurized intermittently as a response to scarcity of water or other
resources. Microbiological and epidemiological evidence indicates that in some contexts IWS is associated with
increased levels of fecal contamination and increased risk of diarrheal disease among end users.
In our initial quantitative microbial risk assessment (QMRA) using E. coli counts observed at IWS taps and
pathogen to E. coli ratios in sewage, we estimated that IWS could account for 17.2 million infections causing 4.52
million cases of diarrhea, 109,000 disability-adjusted life years, and 1,560 deaths among the 925 million exposed to
IWS globally. We then used dead-end ultrafiltation (DEUF) and droplet digital PCR (ddPCR) to perform microbial
sampling of two IWSs in India and QMRA to estimate the risks to human health attributable to IWS in India. During
our microbial sampling in Jaipur, we detected gene targets associated with Cryptosporidium spp., Giardia lamblia,
and enterotoxigenic E. coli (ETEC) concurrently with culturable E. coli in groundwater samples from tube wells. In
Nagpur, we observed a significant increase in the proportion of samples positive for culturable E. coli and gene
targets associated with waterborne pathogens at household taps served by IWS compared to those served by
continuous water supply. At household taps served by IWS we detected genes associated with ETEC, Shigella spp.,
norovirus GI and Gii, adenovirus, Cryptosporidium spp., and Giardia lamblia. Our QMRA estimates that the daily
risks of infection for Giardia, Cryptosporidium, norovirus, adenovirus, and Shigella exceed the US EPA acceptable
annual threshold of 1 in 10,000 at the 10th percentile. At the 10th percentile of daily risk, IWS could account for up to
11 million Giardia infections, 60 million Cryptosporidium infections, and 2.17 million Shigella infections annually
among the 460 million Indians served by IWS.
Collectively, the results of our work indicate that, even given large uncertainty and variability, the public
health risks associated with IWS likely exceed acceptable risk levels established by the WHO and US EPA. Our
findings also indicate that measuring waterborne pathogens in drinking water at levels relevant to risk-based
thresholds is unlikely via DEUF and ddPCR. Given this limitation, risk assessment and management will likely
continue to rely on culture-based enumerations with large uncertainty and unclear relevance to risk-based standards.