Source Water, Environment, and Disease Risk in North American Cities

Amy L. Greer1, Victoria Ng1, Alexander White1 & David N. Fisman1,2

email: amy.greer@sickkids.ca

1The Research Institute of the Hospital for Sick Children 2Ontario Public Health Laboratories Branch

Drink it In

My presentation today

Human health and the environment

Hypothesis and methodology

Examples: Norovirus, Legionellosis, Campylobacter and Giardia

Moving towards a more integrated point of view

Water & Human Health

The Canadian Context

Outbreaks of waterborne diseases

in Canada have shown:

1.how easily water can be contaminated

2.how damaging the consequences can be

(Greer et al., 2008)

A Multi-Barrier Approach

• Source water protection• Effective water treatment• Protection of the water distribution system• Adequate testing and training

What is Source Water?

• Source water is untreated water from streams, lakes or underground aquifers that supplies private wells and public drinking water systems– surface water (74% of Canadians)– groundwater (26% Canadians)

Source Water Ecology

Freshwater ecosystems include the animal, plant and microbial communities in lakes, rivers and

ponds

•Microbes such as bacteria, bacteria-like organisms , viruses, protozoa, helminths, and protists are vital components of the aquatic ecosystem

Environmental Reservoirs

• Movement and persistence of microbes in the absence of human hosts

• Exposure to few propagules can cause human infection

• Multi-barrier approach is good for some pathogens but not others

Multi-barrier

Approach

Question & Hypothesis

What environmental factors are associated with an increased frequency of outbreaks?

Hypothesis: Environmental factors that increase pathogen survival, persistence or proliferation in

the source water environment will be related temporally and spatially to human outbreaks

WEATHER, WATER & GIARDIA IN PHILADELPHIA, 1994-2007

Victoria Ng & David Fisman

Giardia lamblia• Most common protozoan agent of diarrheal

illness in North America • Late summer/early fall seasonality• Zoonotic• Cysts measure 7 to 14 mμ• Cysts are resistant to extreme environmental

conditions• Chlorine typically does not destroy the cysts

Cases with a History of Water Exposure

IRR P IRR PMean temperature, °C 1.05 0.32 0.96 1.14 - - - -

Precipitation, mm 0.60 0.15 0.30 1.20 - - - -Mean dew point temperature, °C 1.01 0.77 0.94 1.08 - - - -

Delaware River pH level 3.69 0.10 0.76 17.77 - - - -Schuykill River level (feet) 0.47 0.02 0.24 0.89 - - - -

Schuykill River level (feet) - 4 week lag 0.41 0.01 0.21 0.78 0.41 0.01 0.21 0.78

IRR P IRR PMean temperature, °C 1.03 0.34 0.97 1.09 - - - -

Precipitation, mm 0.72 0.15 0.46 1.12 - - - -Mean dew point temperature, °C 1.02 0.36 0.98 1.07 - - - -

Delaware River pH level 2.04 0.19 0.70 5.95 - - - -Schuykill River level (feet) 0.56 0.01 0.36 0.88 - - - -

Schuykill River level (feet) - 4 week lag 0.48 0.00 0.30 0.78 0.48 0.00 0.30 0.78

n = 96 (history of water exposure with known onset)

n = 225 (history of water exposure amongst all cases)

Multivariate model95% CI

Multivariate model95% CI

Exposure variablesUnivariate model

95% CI

Exposure variablesUnivariate model

95% CI

Cases with a Known Onset & History of Water Exposure

0

1

2

3

4

5

6

35 30 25 20 15 10 5

Days Prior to Case Occurrence

Od

ds R

ati

o

An increase in the risk of giardiasis is seen with decreasing river level in the SchuykillRiver at a 24 to 26 day lag prior to case occurrence

SEASONAL DRIVERS OF NOROVIRUS OUTBREAKS IN THE GREATER TORONTO AREA, 2005 - 2008

Amy Greer, Steven Drews & David Fisman

(www.news.bbc.co.uk)

New York

DurhamN=22

YorkN=14

PeelN=23

HaltonN=46

Legend: Norovirus Outbreaks per 10,000 Residents

0.170.210.41

0.601.15

Ontario

Norovirus

• Norovirus is the most common, non-bacterial cause of gastroenteritis

• “wintertime vomiting disease”• Source water contaminated by infected sewage or

wastewater • 27 to 38 nm • Chlorination and filtration are considered insufficient to

remove

Lake Ontario temperature ≤ 4 degrees C

High flow in the Don River

EPIDEMIOLOGIC PROFILE OF LEGIONELLOSIS IN THE GTA: 1978 TO 2006

Victoria Ng & David Fisman

(www.news.bbc.co.uk)

Legionella sp.

• Transmission occurs when people breathe in a mist or vapour contaminated with the bacteria

• Late summer to early autumn predominance• Bacteria occur in all aquatic environments with

their primary hosts, free-living protozoa• Chlorination and flushing of pipes has limited

effect

Case-Crossover Results

• Risk of infection increased with low river and creek levels. Acute effects were seen 25 to 31 days prior to case occurrence (OR 3.55, 95% C.I 2.38-5.29)

• Risk of infection increased with decreasing lake temperature (OR 1.33, 95% C.I 1.08-1.64) with 25 to 28 day lag

• Risk of infection increased with increasing humidity with 30 to 34 day lag (OR 1.34, 95% C.I 1.14 to 1.57)

0

1

2

3

4

5

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35 30 25 20 15 10 5 0

Days Prior to Case Occurrence

Od

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ati

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GTA, average river and lake levels: OR 3.55 [95% C.I, 2.38-5.29] with 25 to 31 day lag

Similar Results Found in Three Major Cities• GTA, average river and lake levels: OR 3.55 [95%

C.I, 2.38-5.29] with 25 to 31 day lag

• Philadelphia, Schuykill River level: OR 2.48 [95% C.I, 1.39-4.42] with 25 to 31 day lag

• Hamilton, Stoney Creek level: OR 5.24 [95% C.I, 2.07-13.29] with 25 to 28 day lag (OR 2.80 with 25 to 31 day lag)

WATER & CAMPYLOBACTER IN PHILADELPHIA, 1994 - 2007

Alexander White & David Fisman

(www.news.bbc.co.uk)

Campylobacter sp.

• Leading cause of acute bacterial gastroenteritis in both developed and developing countries

• Summertime seasonality

• Zoonotic

• Increased humidity and low water temperature increase campylobacter colonization and survival rates

• Multi-barrier approach typically sufficient

<0.0011.02 (1.01 1.03)River temperature (oC) (4 week lag)

0.0020.63 (0.48 0.84)River pH (4 week lag)

<0.0010.943 (0.913 0.967)Dissolved oxygen (mg/L)

0.8621.01 (0.99 1.01)Precipitation (mm)

0.3421.11 (1.08 1.13)UV-index

<0.0011.027 (1.021 1.033)Temperature (oC)

0.0011.06 (1.03 1.11)Humidity

P valueIRR (95% CI)Exposure

<0.0011.02 (1.01 1.03)River temperature (oC) (4 week lag)

0.0020.63 (0.48 0.84)River pH (4 week lag)

<0.0010.943 (0.913 0.967)Dissolved oxygen (mg/L)

0.8621.01 (0.99 1.01)Precipitation (mm)

0.3421.11 (1.08 1.13)UV-index

<0.0011.027 (1.021 1.033)Temperature (oC)

0.0011.06 (1.03 1.11)Humidity

P valueIRR (95% CI)ExposureTable 1 Univariate analysis of environmental risk factors

<0.0010.915 (0.877 0.955)River temperature (4 week lag)

0.0141.03 (1.01 1.07)Temperature

0.0031.07 (1.02 1.12)Humidity

P valueIRR (95% CI)Exposure

<0.0010.915 (0.877 0.955)River temperature (4 week lag)

0.0141.03 (1.01 1.07)Temperature

0.0031.07 (1.02 1.12)Humidity

P valueIRR (95% CI)ExposureTable 2 Multivariable analysis of environmental risk factors

Disease Risk and Environment

• Microbes are present in the aquatic ecosystem• Some of these are pathogenic to humans• Environmental conditions can have an indirect

impact on disease occurrence in the community by influencing the presence, persistence and proliferation of pathogens in the aquatic ecosystem

• A better understanding of the mechanisms involved will help us to better mitigate the risks

Moving Beyond the Disciplines

• A fully dimensional understanding of infectious disease reaches across scales

• Medicine and public health is enriched by insights from across science and engineering

Colon et al. 2008

Seeking Out A New Paradigm

• Many pathogens infect humans through a wide variety of ecological pathways

• Pathogens have complex and somewhat mysterious relationships with the environment

• Health issues now encompass an individual's complex relationship with the global environment

• Patterns of disease expand across scales, and explanations must move beyond old paradigms to explore these relationships