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Precipitation, Raw Water Quality, Drinking Water Treatment and Gastrointestinal Illness
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Background

On numerous occasions, outbreaks of acute gastrointestinal illnesses (AGI) have been linked to municipal drinking water in the industrialised world. Many of the reported outbreaks were observed after heavy rainfall events, which suggests that such events could result in a deterioration in the quality of drinking water. The observed drinking water-related outbreaks are, however, probably just the tip of the iceberg, and the extent to which public drinking water also influences the endemic level of gastroenteritis during non-outbreak periods is largely unknown. With climate change projected to increase the frequency of extreme weather events, data for preventive actions are needed now, to ensure safe drinking water today and in the future. The primary aim of this thesis is to increase the knowledge of the extent to which rainfall can still be a risk for insufficient drinking water quality, even with modern drinking water production methods. We aim to study if the incidence of gastroenteritis during normal endemic levels can be associated with water quality and the efficacy of pathogen elimination in different treatment processes. The thesis focuses first on AGI in the Gothenburg population and how precipitation affects its main fresh water supply (papers I-III); this is followed by a broader comparison of AGI in 20 cities across Sweden (Paper IV).

Methods

Observational time series data was used for all papers to construct generalized additive regression models, using smooth functions to adjust for long-term trends. Delayed effects on the outcome were evaluated using distributed lag non-linear models. In Paper I, the raw water-quality data for the river Göta älv were analysed – this water is used to produce drinking water for the population living in the north part of City of Gothenburg. The short-term variation of daily mean turbidity measurements and samples of three different types of indicator bacteria were modelled with daily precipitation using seven years of data. In papers II and III, the analyses aimed to determine whether the daily incidence of AGI in the population which households received drinking water produced from the river water could be associated with precipitation. As a measure of AGI, we used four years of data on the daily number of phone calls to the nurse advice line about vomiting, diarrhoea or abdominal pain (Paper II), and six years of data of the daily number of visits to health care clinics, when individuals were diagnosed with gastrointestinal infections (Paper III). Paper III also evaluates the similarities and differences between the frequency of nurse advice calls and primary health care visits. Paper IV analyses and compares the occurrence and seasonal patterns of nurse advice calls in twenty cities in Sweden, using seven years of data. The water treatment technique used by the public drinking water plants was obtained, and the processes theoretical efficacy of pathogen elimination was determined. The extent of AGI calls in relation to the pathogen elimination efficacy was analysed using a binomial regression design, adjusting for population size, age distribution and geographical area.

Results

We observed a strong relation between precipitation and the water quality in the Göta älv. A heavy rainfall event was related to increased concentrations of E. coli bacteria for several days, with the peak increase two days after the event. Precipitation was found to affect raw water quality parameters across all seasons. Heavy precipitation was also associated with a significant increase in the daily number of nurse advice calls due to AGI symptoms, with the number of calls peaking five days later. Consecutive wet weather periods were associated with both an increased number of AGI calls, as well as visits to clinics that led to diagnoses of AGI. Finally, we observed in Paper IV that cities with a higher pathogen elimination efficacy in their drinking water utility had a lower amount of AGI calls. The relations applied both to surface water and groundwater utilities, although the protective effect of a more advanced drinking water treatment on AGI was observed to be most significant in cities with surface water plants during the winter season.

Conclusions

The results suggest it is possible to reduce the occurrence of endemic gastroenteritis with a more advanced treatment process for drinking water. The delay between a heavy rainfall event (and the resulting decrease in raw water quality) and the increased number of nurse advice calls suggests viruses are the main cause, as the timing is consistent with viral incubation times. A viral transmission was also proposed when comparing different cities, as a more advanced water treatment process seems to be most beneficial during seasons where viruses are acknowledged as the main cause of AGI. Our research suggests that upgrades to drinking water treatment techniques, especially those aiming to better eliminate viruses, are warranted

Place, publisher, year, edition, pages
Umeå: Umeå University , 2015. , 36 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1751
National Category
Environmental Health and Occupational Health Public Health, Global Health, Social Medicine and Epidemiology
Research subject
Epidemiology
Identifiers
URN: urn:nbn:se:umu:diva-108545ISBN: 978-91-7601-339-7 (print)OAI: oai:DiVA.org:umu-108545DiVA: diva2:853512
Public defence
2015-10-09, Triple Helix, Samverkanshuset, Umeå universitet, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2015-09-18 Created: 2015-09-14 Last updated: 2015-09-17Bibliographically approved
List of papers
1. Precipitation Effects on Microbial Pollution in a River: Lag Structures and Seasonal Effect Modification
Open this publication in new window or tab >>Precipitation Effects on Microbial Pollution in a River: Lag Structures and Seasonal Effect Modification
2014 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 5Article in journal (Refereed) Published
Abstract [en]

Background: The river Gota Alv is a source of freshwater for 0.7 million swedes. The river is subject to contamination from sewer systems discharge and runoff from agricultural lands. Climate models projects an increase in precipitation and heavy rainfall in this region. This study aimed to determine how daily rainfall causes variation in indicators of pathogen loads, to increase knowledge of variations in river water quality and discuss implications for risk management. Methods: Data covering 7 years of daily monitoring of river water turbidity and concentrations of E. coli, Clostridium and coliforms were obtained, and their short-term variations in relation with precipitation were analyzed with time series regression and non-linear distributed lag models. We studied how precipitation effects varied with season and compared different weather stations for predictive ability. Results: Generally, the lowest raw water quality occurs 2 days after rainfall, with poor raw water quality continuing for several more days. A rainfall event of >15 mm/24-h (local 95 percentile) was associated with a three-fold higher concentration of E. coli and 30% higher turbidity levels (lag 2). Rainfall was associated with exponential increases in concentrations of indicator bacteria while the effect on turbidity attenuated with very heavy rainfall. Clear associations were also observed between consecutive days of wet weather and decreased water quality. The precipitation effect on increased levels of indicator bacteria was significant in all seasons. Conclusions: Rainfall elevates microbial risks year-round in this river and freshwater source and acts as the main driver of varying water quality. Heavy rainfall appears to be a better predictor of fecal pollution than water turbidity. An increase of wet weather and extreme events with climate change will lower river water quality even more, indicating greater challenges for drinking water producers, and suggesting better control of sources of pollution.

National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:umu:diva-91062 (URN)10.1371/journal.pone.0098546 (DOI)000336790800048 ()
Funder
Swedish Research Council Formas, 10-104
Available from: 2014-07-11 Created: 2014-07-10 Last updated: 2017-12-05Bibliographically approved
2. Association between precipitation upstream of a drinking water utility and nurse advice calls relating to acute gastrointestinal illnesses
Open this publication in new window or tab >>Association between precipitation upstream of a drinking water utility and nurse advice calls relating to acute gastrointestinal illnesses
2013 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 7, e69918Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: The River Göta Älv is a source of fresh-water for the City of Gothenburg (Sweden). We recently identified a clear association between upstream precipitation and indicator bacteria concentrations in the river water outside the intake to the drinking water utility. This study aimed to determine if variation in the incidence of acute gastrointestinal illnesses is associated with upstream precipitation.

METHODS: We acquired data, covering 1494 days, on the daily number of telephone calls to the nurse advice line from citizens in Gothenburg living in areas with Göta Älv as a fresh-water supply. We separated calls relating to gastrointestinal illnesses from other medical concerns, and analyzed their association with precipitation using a distributed lag non-linear Poisson regression model, adjusting for seasonal patterns and covariates. We used a 0-21-day lag period for precipitation to account for drinking water delivery times and incubation periods of waterborne pathogens.

RESULTS: The study period contained 25,659 nurse advice calls relating to gastrointestinal illnesses. Heavy rainfall was associated with increased calls the same day and around 5-6 days later. Consecutive days of wet weather were also found to be associated with an increase in the daily number of gastrointestinal concerns. No associations were identified between precipitation and nurse advice calls relating to other medical concerns.

CONCLUSION: An increase in nurse advice calls relating to gastrointestinal illnesses around 5-6 days after heavy rainfall is consistent with a hypothesis that the cause could be related to drinking water due to insufficient barriers in the drinking water production, suggesting the need for improved drinking water treatment.

National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:umu:diva-80995 (URN)10.1371/journal.pone.0069918 (DOI)000322064300125 ()23875009 (PubMedID)
Available from: 2013-09-30 Created: 2013-09-30 Last updated: 2017-12-06Bibliographically approved
3. Precipitation and primary health care visits for gastrointestinal illness in Gothenburg, Sweden
Open this publication in new window or tab >>Precipitation and primary health care visits for gastrointestinal illness in Gothenburg, Sweden
2015 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 5, e0128487Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: The river Göta Älv is a source of freshwater for the City of Gothenburg, Sweden, and we recently identified a clear influence of upstream precipitation on concentrations of indicator bacteria in the river water, as well as an association with the daily number of phone calls to the nurse advice line related to acute gastrointestinal illnesses (AGI calls). This study aimed to examine visits to primary health-care centers owing to similar symptoms (AGI visits) in the same area, to explore associations with precipitation, and to compare variability in AGI visits and AGI calls.

METHODS: We obtained data covering six years (2007-2012) of daily AGI visits and studied their association with prior precipitation (0-28 days) using a distributed lag nonlinear Poisson regression model, adjusting for seasonal patterns and covariates. In addition, we studied the effects of prolonged wet and dry weather on AGI visits. We analyzed lagged short-term relations between AGI visits and AGI calls, and we studied differences in their seasonal patterns using a binomial regression model.

RESULTS: The study period saw a total of 17,030 AGI visits, and the number of daily visits decreased on days when precipitation occurred. However, prolonged wet weather was associated with an elevated number of AGI visits. Differences in seasonality patterns were observed between AGI visits and AGI calls, as visits were relatively less frequent during winter and relatively more frequent in August, and only weak short-term relations were found.

CONCLUSION: AGI visits and AGI calls seems to partly reflect different types of AGI illnesses, and the patients' choice of medical contact (in-person visits versus phone calls) appears to depend on current weather conditions. An association between prolonged wet weather and increased AGI visits supports the hypothesis that the drinking water is related to an increased risk of AGI illnesses.

Place, publisher, year, edition, pages
Public Library Science, 2015
National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:umu:diva-103837 (URN)10.1371/journal.pone.0128487 (DOI)000355187300116 ()26020929 (PubMedID)
Available from: 2015-06-02 Created: 2015-06-02 Last updated: 2017-12-04Bibliographically approved
4. An Association between the Efficacy of Water Treatment Processes and Endemic Gastrointestinal Illness: A Multi-City Study of Telephone Triage Data in Sweden
Open this publication in new window or tab >>An Association between the Efficacy of Water Treatment Processes and Endemic Gastrointestinal Illness: A Multi-City Study of Telephone Triage Data in Sweden
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Public Health, Global Health, Social Medicine and Epidemiology
Identifiers
urn:nbn:se:umu:diva-108543 (URN)
Available from: 2015-09-14 Created: 2015-09-14 Last updated: 2015-09-17

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